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Electronic doping of organic semiconductors is essential for their usage in highly efficient optoelectronic devices. Although molecular and metal complex-based dopants have already enabled significant progress of devices based on organic semiconductors, there remains a need for clean, efficient and low-cost dopants if a widespread transition towards larger-area organic electronic devices is to occur. Here we report dimethyl sulfoxide adducts as p-dopants that fulfil these conditions for a range of organic semiconductors. These adduct-based dopants are compatible with both solution and vapour-phase processing. We explore the doping mechanism and use the knowledge we gain to 'decouple' the dopants from the choice of counterion. We demonstrate that asymmetric p-doping is possible using solution processing routes, and demonstrate its use in metal halide perovskite solar cells, organic thin-film transistors and organic light-emitting diodes, which showcases the versatility of this doping approach.

A poly(methacrylate) with benzocyclobutene side chains, CL, has been synthesized by radical polymerization for use as a crosslinking additive for a previously reported benzocyclobutene-functionalized fullerene, PCBCB, which can be thermally insolubilized following solution processing. Films of PCBCB incorporating CL and n-doped with (IrCp*Cp)2 exhibit in-plane electrical conductivities around ten times higher than those of n-doped films without CL, while the use of CL also reduces leaching of dopant ions from the film upon washing. The performance and stability of perovskite solar cells using insolubilized PCBCB:CL, insolubilized PCBCB, or PCBM as top electron-extraction layers are compared; cells with undoped PCBCB:CL extraction layers exhibit higher average and maximum power conversion efficiencies (16 and 18.5%, respectively) than their PCBM and PCBCB counterparts. Devices with undoped PCBCB:CL extraction layers also showed excellent thermal stability, retaining 92% of their stabilized power output after aging for 3000 h at 85 °C in the dark in a nitrogen atmosphere.

Although metal halide perovskite photovoltaics have shown an unprecedented rise in power conversion efficiency (PCE), they remain far from their theoretical PCE limit. Among the highest efficiencies to date are delivered when polycrystalline films are enhanced via “molecular passivation”, but this can introduce new instabilities, in particular under severe accelerated aging conditions (e.g., at 85 °C in the dark or under full spectrum simulated sunlight). Here, we utilize a benzylammonium bromide passivation treatment to improve device performance, achieving the champion stabilized power output (SPO) of 19.5 % in a p-i-n device architecture. We correlate the improved device performance with a significant increase in charge carrier diffusion lengths, mobilities, and lifetimes. Furthermore, treated devices maintain an increased performance during 120 h combined stressing under simulated full spectrum sunlight at 85 °C, indicating that enhancement from this passivation treatment is sustained under harsh accelerated aging conditions. This is a crucial step toward real-world operation-relevant passivation treatments.

Lead halide perovskite nanocrystals (NCs) are promising for applications in light emitting devices owing to a strong emission spectrum that is tunable throughout the visible region by altering halide composition. However, in mixed-halide perovskite systems photoinduced migration drives formation of halide-segregated domains, altering the emission spectrum. The mechanism by which this segregation occurs is currently the subject of intense investigation. Processes involving the perovskite surface are expected to be of enhanced prevalence in NCs due to their large surface area to volume ratio. In this work, we use transient absorption spectroscopy to probe the excited-state dynamics of NCs before and after halide segregation. Comparison of global fit spectra of the measured signals suggests the accumulation of iodide at the surface, resulting in a redshifted emission spectrum.

We analyze nucleation-controlled nanocrystal growth in a solution containing surface-binding molecular ligands, which can also nucleate compact layers on the crystal surfaces. We show that, if the critical nucleus size for ligands is larger and the nucleation barrier is lower than those for crystal atoms, the ligands nucleate faster than the atoms on relatively wide crystal facets but much slower, if at all, on narrow facets. Such competitive nucleation of ligands and atoms results in ligands covering predominantly wider facets, thus excluding them from the growth process, and acts as a selection mechanism for the growth of crystals with narrower facets, the so-called nanoplatelets. The theory is confirmed by Monte Carlo simulations and validated experimentally for CsPbBr3 nanoplatelets grown from solution. We find that the anisotropic crystal growth is controlled by the growth temperature and the strength of surface bonding for the passivating molecular ligands.

Light-emitting diodes (LEDs) made from metal halide perovskites have demonstrated external electroluminescent quantum efficiencies (EQEEL) in excess of 20%. However, their poor operational stability, resulting in lifetimes of only tens to hundreds of hours, needs to be dramatically improved prior to commercial use. There is little consensus in the community upon which factors limit the stability of these devices. Here, we investigate the role played by ammonium cations on the operational stability. We vary the amount of phenylethylammonium bromide, a widely used alkylammonium salt, that we add to a precursor solution of CsPbBr3 and track changes in stability and EQEEL. We find that while phenylethylammonium bromide is beneficial in achieving high efficiency, it is highly detrimental to operational stability. We investigate material properties and electronic characteristics before and after degradation and find that both a reduction in the radiative efficiency of the emitter and significant changes in current–voltage characteristics explain the orders of magnitude drop in the EQEEL, which we attribute to increased ionic mobility. Our results suggest that engineering new contacts and further investigation into materials with lower ionic mobility should yield much improved stability of perovskite LEDs.

Double perovskites have recently emerged as possible alternatives to lead-based halide perovskites for photovoltaic applications. In particular, Cs2AgBiBr6 has been the subject of several studies b...

Despite rapid advancements in power conversion efficiency in the last decade, perovskite solar cells still perform below their thermodynamic efficiency limits. Non-radiative recombination, in particular, has limited the external radiative efficiency and open circuit voltage in the highest performing devices. We review the historical progress in enhancing perovskite external radiative efficiency and determine key strategies for reaching high optoelectronic quality. Specifically, we focus on non-radiative recombination within the perovskite layer and highlight novel approaches to reduce energy losses at interfaces and through parasitic absorption. By strategically targeting defects, it is likely that the next set of record-performing devices with ultra-low voltage losses will be achieved.

Successful chemical doping of metal halide perovskites with small amounts of heterovalent metals has attracted recent research attention because of its potential to improve long-term material stability and tune absorption spectra. However, some additives have been observed to impact negatively on optoelectronic properties, highlighting the importance of understanding charge-carrier behavior in doped metal halide perovskites. Here, we present an investigation of charge-carrier trapping and conduction in films of MAPbBr3 perovskite chemically doped with bismuth. We find that the addition of bismuth has no effect on either the band gap or exciton binding energy of the MAPbBr3 host. However, we observe a substantial enhancement of electron-trapping defects upon bismuth doping, which results in an ultrafast charge-carrier decay component, enhanced infrared emission, and a notable decrease of charge-carrier mobility. We propose that such defects arise from the current approach to Bi-doping through addition of BiBr3, which may enhance the presence of bromide interstitials.

The carrier-type of the emerging photovoltaic Sb2Se3 was evaluated for both thin films and bulk crystals via a range of complementary techniques. X-ray photoelectron spectroscopy (XPS), hot probe, Hall effect, and surface photovoltage spectroscopy showed films and crystals synthesized from the Sb2Se3 granulate material to be n-type with chlorine identified as an unintentional n-type dopant via secondary ion mass spectrometry analysis. The validity of chlorine as a dopant was confirmed by the synthesis of intrinsic crystals from metallic precursors and subsequent deliberate n-type doping by the addition of MgCl2. Chlorine was also shown to be a substitutional n-type shallow dopant by density functional theory calculations. TiO2/Sb2Se3 n–n isotype heterojunction solar cells with 7.3% efficiency are subsequently demonstrated, with band alignment analyzed via XPS.

Since the emergence of lead halide perovskites for photovoltaic research, there has been mounting effort in the search for alternative compounds with improved or complementary physical, chemical, or optoelectronic properties. Here, we report the discovery of Cu2AgBiI6: a stable, inorganic, lead-free wide-band-gap semiconductor, well suited for use in lead-free tandem photovoltaics. We measure a very high absorption coefficient of 1.0 × 105 cm–1 near the absorption onset, several times that of CH3NH3PbI3. Solution-processed Cu2AgBiI6 thin films show a direct band gap of 2.06(1) eV, an exciton binding energy of 25 meV, a substantial charge-carrier mobility (1.7 cm2 V–1 s–1), a long photoluminescence lifetime (33 ns), and a relatively small Stokes shift between absorption and emission. Crucially, we solve the structure of the first quaternary compound in the phase space among CuI, AgI and BiI3. The structure includes both tetrahedral and octahedral species which are open to compositional tuning and chemical substitution to further enhance properties. Since the proposed double-perovskite Cs2AgBiI6 thin films have not been synthesized to date, Cu2AgBiI6 is a valuable example of a stable Ag+/Bi3+ octahedral motif in a close-packed iodide sublattice that is accessed via the enhanced chemical diversity of the quaternary phase space.

Looking beyond energy harvesting, metal-halide perovskites offer great opportunities to revolutionise large-area photodetection technologies due to their high absorption coefficients, long diffusion lengths, low trap densities and simple processability. However, successful extraction of photocarriers from perovskites and their conversion to electrical signals remain challenging due to the interdependency of photogain and dark current density. Here we report hybrid hetero-phototransistors by integrating perovskites with organic semiconductor transistor channels to form either “straddling-gap” type-I or “staggered-gap” type-II heterojunctions. Our results show that gradual transforming from type-II to type-I heterojunctions leads to increasing and tuneable photoresponsivity with high photogain. Importantly, with a preferential edge-on molecular orientation, the type-I heterostructure results in efficient photocarrier cycling through the channel. Additionally, we propose the use of a photo-inverter circuitry to assess the phototransistors’ functionality and amplification. Our study provides important insights into photocarrier dynamics and can help realise advanced device designs with “on-demand” optoelectronic properties., Realizing phototransistors based on hybrid perovskite heterostructures with tuneable photodetection remains a challenge. Here, the authors integrate metal-halide perovskites into organic semiconductors to design hybrid heterojunction phototransistors with state-of-the-art performance.

The past few years witnessed the rise of halide perovskites as prominent materials for a wide range of optoelectronic applications. However, oxide perovskites have a much longer history and are pivotal in many technological applications. As of today, a rational connection between these important materials is missing. Here, we explore this missing link and develop a novel concept of perovskite analogs, which led us to identify a new semiconductor, Ba2AgIO6. It exhibits an electronic band structure remarkably similar to that of our recently discovered halide double perovskite Cs2AgInCl6, but with a band gap in the visible range at 1.9 eV. We show that Ba2AgIO6 and Cs2AgInCl6 are analogs of the well-known transparent conductor BaSnO3. We synthesize Ba2AgIO6 following a low-temperature solution process, and we perform crystallographic and optical characterizations. Ba2AgIO6 is a cubic oxide double perovskite with a direct low gap, opening new opportunities in perovskite-based electronics optoelectronics and e...

Organic hole-transporting materials (HTM) have shown excellent ability in achieving high efficiency\ud perovskite solar cells. However, their high cost significantly limits their applications in scaling-up\ud perovskite solar cells. Here, we report an efficient, low-cost HTM, called TAT-tBuSty, comprising a\ud central triazatruxene moiety with 3 terminal tert-butoxy styrene groups and 3 hexyl side chains on the\ud indole nitrogen. For the first time, we use an inexpensive liquid precursor to attach the donor ligand to\ud the molecule. This enables purification of the HTM using a silica plug and recrystallization without the\ud need for complicated column chromatography, which is typically required to purify solid-precursorprepared\ud HTMs. We estimate that the cost for the purified TAT-tBuSty is $69.90 g�1, which is 35%\ud cheaper than the widely-used 2,207,70-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,90-spirobifluorene\ud (spiro-OMeTAD; ca. $112.05 g�1). Using this low-cost TAT-tBuSty as the HTM in a caesium-formamidinium\ud mixed-cation perovskite solar cell, we have successfully achieved a champion power conversion efficiency\ud (PCE) of 20.3% (19.4% stabilized efficiency), which is comparable to the efficiency of devices using the\ud reference spiro-OMeTAD HTM. Our work is crucial for up-scaling of next-generation high-performance\ud metal-halide perovskite solar cells.

Lead-free silver–bismuth semiconductors have become increasingly popular materials for optoelectronic applications, building upon the success of lead halide perovskites. In these materials, charge-lattice couplings fundamentally determine charge transport, critically affecting device performance. In this study, we investigate the optoelectronic properties of the recently discovered lead-free semiconductor Cu2AgBiI6 using temperature-dependent photoluminescence, absorption, and optical-pump terahertz-probe spectroscopy. We report ultrafast charge-carrier localization effects, evident from sharp THz photoconductivity decays occurring within a few picoseconds after excitation and a rise in intensity with decreasing temperature of long-lived, highly Stokes-shifted photoluminescence. We conclude that charge carriers in Cu2AgBiI6 are subject to strong charge-lattice coupling. However, such small polarons still exhibit mobilities in excess of 1 cm2 V–1 s–1 at room temperature because of low energetic barriers to formation and transport. Together with a low exciton binding energy of ∼29 meV and a direct band gap near 2.1 eV, these findings highlight Cu2AgBiI6 as an attractive lead-free material for photovoltaic applications.

Mixed-halide perovskites offer bandgap tunability essential for multijunction solar cells; however, a detrimental halide segregation under light is often observed. Here we combine simultaneous in situ photoluminescence and X-ray diffraction measurements to demonstrate clear differences in compositional and optoelectronic changes associated with halide segregation in MAPb(Br0.5I0.5)3 and FA0.83Cs0.17Pb(Br0.4I0.6)3 films. We report evidence for low-barrier ionic pathways in MAPb(Br0.5I0.5)3, which allow for the rearrangement of halide ions in localized volumes of perovskite without significant compositional changes to the bulk material. In contrast, FA0.83Cs0.17Pb(Br0.4I0.6)3 lacks such low-barrier ionic pathways and is, consequently, more stable against halide segregation. However, under prolonged illumination, it exhibits a considerable ionic rearrangement throughout the bulk material, which may be triggered by an initial demixing of A-site cations, altering the composition of the bulk perovskite and reducing its stability against halide segregation. Our work elucidates links between composition, ionic pathways, and halide segregation, and it facilitates the future engineering of phase-stable mixed-halide perovskites.

Space-charge-limited current (SCLC) measurements have been widely used to study the charge carrier mobility and trap density in semiconductors. However, their applicability to metal halide perovskites is not straightforward, due to the mixed ionic and electronic nature of these materials. Here, we discuss the pitfalls of SCLC for perovskite semiconductors, and especially the effect of mobile ions. We show, using drift-diffusion (DD) simulations, that the ions strongly affect the measurement and that the usual analysis and interpretation of SCLC need to be refined. We highlight that the trap density and mobility cannot be directly quantified using classical methods. We discuss the advantages of pulsed SCLC for obtaining reliable data with minimal influence of the ionic motion. We then show that fitting the pulsed SCLC with DD modeling is a reliable method for extracting mobility, trap, and ion densities simultaneously. As a proof of concept, we obtain a trap density of 1.3 × 1013 cm-3, an ion density of 1.1 × 1013 cm-3, and a mobility of 13 cm2 V-1 s-1 for a MAPbBr3 single crystal.

International audience; We present a crystallographic and optoelectronic study of the double perovskite Cs2AgBi1-xInxBr6. From structural characterization we determine that the indium cation shrinks the lattice and shifts the cubic-to-tetragonal phase transition point to lower temperatures. The absorption onset is shifted to shorter wavelengths upon increasing the indium content, leading to wider band gaps, which we rationalize through first-principles band structure calculations. Despite the unfavorable band gap shift, we observe an enhancement in the steadystate photoluminescence intensity, and n-i-p photovoltaic devices present short-circuit current greater than that of neat Cs2AgBiBr6 devices. In order to evaluate the prospects of this material as a solar absorber, we combine accurate absorption measurements with thermodynamic modeling and identify the fundamental limitations of this system. Provided radiative efficiency can be increased and the choice of charge extraction layers are specifically improved, this material could prove to be a useful wide band gap solar absorber.

Hybrid halide perovskites have great potential for application in optoelectronic devices. However, an understanding of some basic properties, such as charge-carrier transport, remains inconclusive, mainly due to the mixed ionic and electronic nature of these materials. Here, we perform temperature-dependent pulsed-voltage space-charge-limited current measurements to provide a detailed look into the electronic properties of methylammonium lead tribromide (${\mathrm{MA}\mathrm{Pb}\mathrm{Br}}_{3}$) and methylammonium lead triiodide (${\mathrm{MA}\mathrm{Pb}\mathrm{I}}_{3}$) single crystals. We show that the background carrier density in these crystals is orders of magnitude higher than that expected from thermally excited carriers from the valence band. We highlight the complexity of the system via a combination of experiments and drift-diffusion simulations and show that different factors, such as thermal injection from the electrodes, temperature-dependent mobility, and trap and ion density, influence the free-carrier concentration. We experimentally determine effective activation energies for conductivity of (349 \ifmmode\pm\else\textpm\fi{} 10) meV for ${\mathrm{MA}\mathrm{Pb}\mathrm{Br}}_{3}$ and (193 \ifmmode\pm\else\textpm\fi{} 12) meV for ${\mathrm{MA}\mathrm{Pb}\mathrm{I}}_{3}$, which includes the sum of all of these factors. We point out that fitting the dark current density-voltage curve with a drift-diffusion model allows for the extraction of intrinsic parameters, such as mobility and trap and ion density. From simulations, we determine a charge-carrier mobility of 12.9 cm${}^{2}$/Vs, a trap density of 1.52 \ifmmode\times\else\texttimes\fi{} 10${}^{13}$ cm${}^{\ensuremath{-}3}$, and an ion density of 3.19 \ifmmode\times\else\texttimes\fi{} 10${}^{12}$ cm${}^{\ensuremath{-}3}$ for ${\mathrm{MA}\mathrm{Pb}\mathrm{Br}}_{3}$ single crystals. Insights into charge-carrier transport in metal-halide perovskite single crystals will be beneficial for device optimization in various optoelectronic applications.

The limited long-term stability of metal halide perovskite-based solar cells is a bottleneck in their drive toward widespread commercial adaptation. The organic hole-transport materials (HTMs) have been implicated in the degradation, and metal oxide layers are proposed as alternatives. One of the most prominent metal oxide HTM in organic photovoltaics is MoO3. However, the use of MoO3 as HTM in metal halide perovskite-based devices causes a severe solar cell deterioration. Thus, the formation of the MoO3/CH3NH3PbI3-xClx (MAPbI3-xClx) heterojunction is systematically studied by synchrotron-based hard X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy. Upon MoO3 deposition, significant chemical interaction is induced at the MoO3/MAPbI3-xClx interface: substoichiometric molybdenum oxide is present, and the perovskite decomposes in the proximity of the interface, leading to accumulation of PbI2 on the MoO3 cover layer. Furthermore, we find evidence for the formation of new compounds such as PbMoO4, PbN2O2, and PbO as a result of the MAPbI3-xClx decomposition and suggest chemical reaction pathways to describe the underlying mechanism. These findings suggest that the (direct) MoO3/MAPbI3-xClx interface may be inherently unstable. It provides an explanation for the low power conversion efficiencies of metal halide perovskite solar cells that use MoO3 as a hole-transport material and in which there is a direct contact between MoO3 and perovskite.

Perovskite solar cells deliver high efficiencies, but are often made from high-cost bespoke chemicals, such as the archetypical hole-conductor, 2,2′,7,7′-tetrakis(N,N-di-p-methoxy-phenylamine)-9-9′-spirobifluorene (spiro-OMeTAD). Herein, new charge-transporting carbazole-based enamine molecules are reported. The new hole conductors do not require chemical oxidation to reach high power conversion efficiencies (PCEs) when employed in n-type-intrinsic-p-type perovskite solar cells; thus, reducing the risk of moisture degrading the perovskite layer through the hydrophilicity of oxidizing additives that are typically used with conventional hole conductors. Devices made with these new undoped carbazole-based enamines achieve comparable PCEs to those employing doped spiro-OMeTAD, and greatly enhanced stability under 85 °C thermal aging; maintaining 83% of their peak efficiency after 1000 h, compared with spiro-OMeTAD-based devices that degrade to 26% of the peak PCE within 24 h. Furthermore, the carbazole-based enamines can be synthesized without the use of organometallic catalysts and complicated purification techniques, lowering the material cost by one order of magnitude compared with spiro-OMeTAD. As a result, we calculate that the overall manufacturing costs of future photovoltaic (PV) modules are reduced, making the levelized cost of electricity competitive with silicon PV modules.

Emerging photovoltaics (PVs) focus on a variety of applications complementing large scale electricity generation. Organic, dye-sensitized, and some perovskite solar cells are considered in building integration, greenhouses, wearable, and indoor applications, thereby motivating research on flexible, transparent, semitransparent, and multi-junction PVs. Nevertheless, it can be very time consuming to find or develop an up-to-date overview of the state-of-the-art performance for these systems and applications. Two important resources for recording research cells efficiencies are the National Renewable Energy Laboratory chart and the efficiency tables compiled biannually by Martin Green and colleagues. Both publications provide an effective coverage over the established technologies, bridging research and industry. An alternative approach is proposed here summarizing the best reports in the diverse research subjects for emerging PVs. Best performance parameters are provided as a function of the photovoltaic bandgap energy for each technology and application, and are put into perspective using, e.g., the Shockley-Queisser limit. in all cases, the reported data correspond to published and/or properly described certified results, with enough details provided for prospective data reproduction. Additionally, the stability test energy yield is included as an analysis parameter among state-of-the-art emerging PVs., VDI/VD Innovation + Technik GmbH; SAOT - German Research Foundation (DFG)German Research Foundation (DFG); DFGGerman Research Foundation (DFG)European Commission [INST 90/917-1 FUGG, 182849149, SFB 953]; Energy Conversion Systems-from Materials to Devices [IGK 2495]; grant "ELF-PV-Design and development of solution processed functional materials for the next generations of PV technologies" [44-6521a/20/4]; grant "Solar Factory of the Future" [FKZ 20.2-3410.5-4-5]; SolTech Initiative by the Bavarian State Government; FAPESPFundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2017/11986-5]; ShellRoyal Dutch Shell; ANP (Brazil's National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation; National Science FoundationNational Science Foundation (NSF) [CBET-1702591]; US Department of Energy, Office of Energy Efficiency and Renewable Energy, Solar Energy Technologies OfficeUnited States Department of Energy (DOE) [34351]; European Research Council under the European Union's Horizon 2020 research and innovation program [742708]; Projekt DEAL, O.A. acknowledges the financial support from the VDI/VD Innovation + Technik GmbH (Project-title: PV-ZUM) and the SAOT funded by the German Research Foundation (DFG) in the framework of the German excellence initiative. C.J.B. acknowledges funding from DFG within INST 90/917-1 FUGG, the SFB 953 (DFG, project no. 182849149) and the IGK 2495 (Energy Conversion Systems-from Materials to Devices). C.J.B. further acknowledges the grants "ELF-PV-Design and development of solution processed functional materials for the next generations of PV technologies" (No. 44-6521a/20/4) and "Solar Factory of the Future" (FKZ 20.2-3410.5-4-5) and the SolTech Initiative by the Bavarian State Government. A.F.N. acknowledges support from FAPESP (Grant 2017/11986-5), Shell and the strategic importance of the support given by ANP (Brazil's National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation. R.R.L. gratefully acknowledges support from the National Science Foundation under grant CBET-1702591. N.K. acknowledges funding by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Solar Energy Technologies Office, Agreement Number 34351. J.N. thanks the European Research Council for support under the European Union's Horizon 2020 research and innovation program (grant agreement No 742708).; Open access funding enabled and organized by Projekt DEAL.

INTRODUCTION Hybrid metal halide perovskites are highly favorable materials for efficient photovoltaic and optoelectronic applications. The mechanisms behind their impressive performance have yet to be fully understood, but they likely depend on atomic-level properties that may be unique to these perovskites. Atomic-resolution transmission electron microscopy is well suited to provide new insights but is challenging because of the highly beam-sensitive nature of hybrid perovskites. RATIONALE We used low-dose scanning transmission electron microscopy (STEM) imaging to determine the microstructure of thin hybrid perovskite films. Thermally evaporated thin films of formamidinium and methylammonium lead triiodide (FAPbI3 and MAPbI3, respectively) were examined on ultrathin carbon-coated copper TEM grids to reveal the nature of boundaries, defects, and decomposition pathways. RESULTS Using low-dose low-angle annular dark field (LAADF) STEM imaging, we obtained atomic-resolution micrographs of FAPbI3 films in the cubic phase. We found that prolonged electron irradiation leads to a loss of FA+ ions, which initially causes the perovskite structure to change to a partially FA+-depleted but ordered perovskite lattice, apparent as light-and-dark checkered patterns in STEM images. Further electron beam exposure leads to the expected deterioration to PbI2 as the final decomposition product. We propose that the observed intermediate checkered pattern is triggered by an initially random, beam-induced loss of FA+, followed by subsequent reordering of FA+ ions. The discovery of this intermediate structure explains why the perovskite structure can sustain significant deviations from stoichiometry and recovers remarkably well from damage. We further revealed the atomic arrangement at interfaces within the hybrid perovskite films. We found that PbI2 precursor remnants commonly encountered in hybrid perovskite films readily and seamlessly intergrow with the FAPbI3 and MAPbI3 lattice and can distort from their bulk hexagonal structure to form a surprisingly coherent transition boundary, exhibiting low lattice misfit and strain. We observed PbI2 domains that nearly perfectly follow the surrounding perovskite structure and orientation, which suggests that PbI2 may seed perovskite growth. These observations help to explain why the presence of excess PbI2 tends not to impede solar cell performance. Images of FAPbI3 grain boundaries further revealed that the long-range perovskite structure is preserved up to the grain boundaries, where sharp interfaces are generally present, without any obvious preferred orientation. Near-120° triple boundaries are most commonly observed at the intersection of three grains, which we generally found to be crystallographically continuous and associated with minimal lattice distortion. Finally, we identified the nature of defects, dislocations, and stacking faults in the FAPbI3 lattice. We discovered dislocations that are dissociated in a direction perpendicular to their glide plane (climb-dissociated), aligned point defects in the form of vacancies on the Pb-I sublattice, and stacking faults corresponding to a shift of half a unit cell, connecting Pb-I columns with I– columns rather than with FA+ columns. CONCLUSION Our findings provide an atomic-level understanding of the technologically important class of hybrid lead halide perovskites, revealing several mechanisms that underpin their remarkable performance. The highly adaptive nature of the perovskite structure upon organic cation loss yields exceptional regenerative properties of partly degraded material. The observation of coherent perovskite interfaces with PbI2 explains the barely diminished optoelectronic performance upon such precursor inclusions, while sharp interfaces between perovskite grains grant a benign nature. Such atomically localized information enables the targeted design of methods to eliminate defects and optimize interfaces in these materials.

All‐inorganic perovskite materials are attractive alternatives to organic‐inorganic perovskites because of their potential for higher thermal stability. While CsPbI3 is compositionally stable under elevated temperatures, the cubic perovskite α‐phase is thermodynamically stable only at >330°C and the low‐temperature perovskite γ−phase is metastable and highly susceptible to non‐perovskite δ‐phase conversion in moisture. Many methods have been reported which show that incorporation of acid (aqueous HI) or “HPbI3” – recently shown to be dimethylammonium lead iodide (DMAPbI3) – lower the annealing temperature required to produce the black, perovskite phase of CsPbI3. The optical and crystallographic data presented here show that DMA can successfully incorporate as an A‐site cation to replace Cs in the CsPbI3 perovskite material. This describes the stabilization and lower phase transition temperature reported in the literature when HI or HPbI3 are used as precursors for CsPbI3. The Cs‐DMA alloy only forms a pure‐phase material up to ∽25% DMA; at higher concentrations the CsPbI3 and DMAPbI3 begin to phase segregate. These alloyed materials are more stable to moisture than neat CsPbI3, but do not represent a fully inorganic perovskite material.

We present the synthesis of formamidinium lead tribromide (FAPbBr3) perovskite nanocrystals through a phosphine oxide route, where in comparison to more traditional syntheses oleylamine is replaced with trioctylphosphine oxide (TOPO). This route has previously been shown to be successful for the inorganic cesium lead tribromide perovskite nanocrystals. We examine the interactions between the precursors via nuclear magnetic resonance spectroscopy (NMR). We confirm the existence of an interaction between FA-oleate and TOPO and use this to guide the optimization of our synthesis. When the reaction is conducted at room temperature, we observe the formation of nanoparticles with high photoluminescence quantum yield (PLQY, ∼70%) at 2.39 eV (518 nm) with little ripening or size defocusing over time. Although we obtain narrow emission peaks, the crystals are irregular in shape—a testament to the impact of the FA-oleate:TOPO interaction. Despite a drop in PLQY in the washed solutions, films made maintain a high PLQY of ∼50% at 2.33 eV (532 nm), which is fortuitously the ideal wavelength for the green emission channel in displays, and we demonstrate 532 nm electroluminescence in light-emitting diodes with an EQE of 3.7%.

Alternatives to lead- and tin-based perovskites for photovoltaics and optoelectronics are sought that do not suffer from the disadvantages of toxicity and low device efficiency of present-day materials. Here we report a study of the double perovskite Cs2TeI6, which we have synthesized in the thin film form for the first time. Exhaustive trials concluded that spin coating CsI and TeI4 using an antisolvent method produced uniform films, confirmed as Cs2TeI6 by XRD with Rietveld analysis. They were stable up to 250 °C and had an optical band gap of ∼1.5 eV, absorption coefficients of ∼6 × 104 cm-1, carrier lifetimes of ∼2.6 ns (unpassivated 200 nm film), a work function of 4.95 eV, and a p-type surface conductivity. Vibrational modes probed by Raman and FTIR spectroscopy showed resonances qualitatively consistent with DFT Phonopy-calculated spectra, offering another route for phase confirmation. It was concluded that the material is a candidate for further study as a potential optoelectronic or photovoltaic material.

Mixed-halide perovskites are essential for use in all-perovskite or perovskite–silicon tandem solar cells due to their tunable bandgap. However, trap states and halide segregation currently present the two main challenges for efficient mixed-halide perovskite technologies. Here photoluminescence techniques are used to study trap states and halide segregation in full mixed-halide perovskite photovoltaic devices. This work identifies three distinct defect species in the perovskite material: a charged, mobile defect that traps charge-carriers in the perovskite, a charge-neutral defect that induces halide segregation, and a charged, mobile defect that screens the perovskite from external electric fields. These three defects are proposed to be MA+ interstitials, crystal distortions, and halide vacancies and/or interstitials, respectively. Finally, external quantum efficiency measurements show that photoexcited charge-carriers can be extracted from the iodide-rich low-bandgap regions of the phase-segregated perovskite formed under illumination, suggesting the existence of charge-carrier percolation pathways through grain boundaries where phase-segregation may occur.

Metal halide perovskite semiconductors have sprung to the forefront of research into optoelectronic devices and materials, largely because of their remarkable photovoltaic efficiency records above 25% in single-junction devices and 28% in tandem solar cells, achieved within a decade of research. Despite this rapid progress, ionic conduction within the semiconductor still puzzles the community and can have a significant impact on all metal halide perovskite-based optoelectronic devices because of its influence upon electronic and optoelectronic processes. This phenomenon thus also makes the interpretation of electrical characterization techniques, which probe the fundamental properties of these materials, delicate and complex. For example, space-charge limited current measurements are widely used to probe defect densities and carrier mobilities in perovskites. However, the influence of mobile ions upon these measurements is significant but has yet to be considered. Here we report the effect of mobile ions upon electronic conductivity during space-charge limited current measurements of MAPbBr3 single crystals and show that conventional interpretations deliver erroneous results. We introduce a pulsed-voltage space-charge limited current procedure to achieve reproducible current-voltage characteristics without hysteresis. From this revised pulsed current-voltage sweep, we elucidate a lower bound trap-density value of 2.8 ± 1.8 × 1012 cm-3 in MAPbBr3 single crystals. This work will lead to more accurate characterization of halide perovskite semiconductors and ultimately more effective device optimization.

The tunable bandgap of metal-halide perovskites has opened up the possibility of tandem solar cells with over 30% efficiency. Iodide-Bromide (I-Br) mixed-halide perovskites are crucial to achieve the optimum bandgap for such tandems. However, when the Br content is increased to widen the bandgap, cells fail to deliver the expected increase in open-circuit voltage (VOC). This loss in VOC has been attributed to photo-induced halide segregation. Here, we combine Fourier Transform Photocurrent Spectroscopy (FTPS) with detailed balance calculations to quantify the voltage loss expected from the halide segregation, providing a means to quantify the VOC losses arising from the formation of low bandgap iodide-rich phases during halide segregation. Our results indicate that, contrary to popular belief, halide segregation is not the dominant VOC loss mechanism in Br-rich wide bandgap cells. Rather, the loss is dominated by the relatively low initial radiative efficiency of the cells, which arises from both imperfections within the absorber layer, and at the perovskite/charge extraction layer heterojunctions. We thus identify that focussing on maximising the initial radiative efficiency of the mixed-halide films and devices is more important than attempting to suppress halide segeregation. Our results suggest that a VOC of up to 1.33 V is within reach for a 1.77 eV bandgap perovskite, even if halide segregation cannot be supressed

Improving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis., This article is based upon work from COST Action StableNextSol MP1307 supported by COST (European Cooperation in Science and Technology). M.V.K., E.A.K., V.B. and A.O. thank the financial support of the United States – Israel Binational Science Foundation (grant no. 2015757). E.A.K., A.A. and I.V.-F. acknowledge partial support from the SNaPSHoTs project in the framework of the German-Israeli bilateral R&D cooperation in the field of applied nanotechnology. M.S.L. thanks the financial support of National Science Foundation (ECCS, award #1610833). S.C., M.Manceau and M.Matheron thank the financial support of European Union’s Horizon 2020 research and innovation programme under grant agreement no 763989 (APOLO project). F.D.R. and T.M.W. would like to acknowledge the support from the Engineering and Physical Sciences Research Council (EPSRC) through the SPECIFIC Innovation and Knowledge Centre (EP/N020863/1) and express their gratitude to the Welsh Government for their support of the Ser Solar programme. P.A.T. acknowledges financial support from the Russian Science Foundation (project No. 19-73-30020). J.K. acknowledges the support by the Solar Photovoltaic Academic Research Consortium II (SPARC II) project, gratefully funded by WEFO. M.K.N. acknowledges financial support from Innosuisse project 25590.1 PFNM-NM, Solaronix, Aubonne, Switzerland. C.-Q.M. would like to acknowledge The Bureau of International Cooperation of Chinese Academy of Sciences for the support of ISOS11 and the Ministry of Science and Technology of China for the financial support (no. 2016YFA0200700). N.G.P. acknowledges financial support from the National Research Foundation of Korea (NRF) grants funded by the Ministry of Science, ICT Future Planning (MSIP) of Korea under contracts NRF-2012M3A6A7054861 and NRF-2014M3A6A7060583 (Global Frontier R&D Program on Center for Multiscale Energy System). CSIRO’s contribution to this work was conducted with funding support from the Australian Renewable Energy Agency (ARENA) through its Advancing Renewables Program. A.F.N gratefully acknowledges support from FAPESP (Grant 2017/11986-5) and Shell and the strategic importance of the support given by ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation. Y.-L.L. and Q.B. acknowledge support from the National Science Foundation Division of Civil, Mechanical and Manufacturing Innovation under award no. 1824674. S.D.S. acknowledges the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (HYPERION, grant agreement no. 756962), and the Royal Society and Tata Group (UF150033). The work at the National Renewable Energy Laboratory was supported by the US Department of Energy (DOE) under contract DE-AC36-08GO28308 with Alliance for Sustainable Energy LLC, the manager and operator of the National Renewable Energy Laboratory. The authors (J.J.B, J.M.L., M.O.R, K.Z.) acknowledge support from the ‘De-risking halide perovskite solar cells’ program of the National Center for Photovoltaics, funded by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Solar Energy Technology Office. The views expressed in the article do not necessarily represent the views of the DOE or the US Government. H.J.S. acknowledges the support of EPSRC UK, Engineering and Physical Sciences Research Council. V.T. and M.Madsen acknowledge ‘Villum Foundation’ for funding of the project CompliantPV, under project no. 13365. M.Madsen acknowledges Danmarks Frie Forskningsfond, DFF FTP for funding of the project React-PV, no. 8022-00389B. M.G. and S.M.Z. thank the King Abdulaziz City for Science and technology (KACST) for financial support. S.V. acknowledges TKI-UE/Ministry of Economic Affairs for financial support of the TKI-UE toeslag project POP-ART (no. 1621103). RC thanks the grants for Development of New Faculty Staff, Ratchadaphiseksomphot Endowment Fund. A.D.C. gratefully acknowledges funding from the European Union’s Horizon 2020 Research and Innovation Program (grant agreement no. 785219-GrapheneCore2 and no. 764047-ESPResSo). M.L.C. and H.X. acknowledges the support from Spanish MINECO for the grant GraPErOs (ENE2016-79282-C5-2-R), the OrgEnergy Excellence Network CTQ2016-81911- REDT, the Agència de Gestiód’Ajuts Universitaris i de Recerca (AGAUR) for the support to the consolidated Catalonia research group 2017 SGR 329 and the Xarxa de Referència en Materials Avançats per a l’Energia (Xarmae). ICN2 is supported by the Severo Ochoa program from Spanish MINECO (Grant no. SEV-2017-0706) and is funded by the CERCA Programme/Generalitat de Catalunya.

Henry J. Snaith is Professor of Physics in the Clarendon Laboratory at the University of Oxford and Fellow of the Royal Society. He has pioneered the field of perovskite solar cells and published more than 300 papers. He is the founder and Chief Scientist Officer of Oxford Photovoltaics, which holds the largest perovskite patent portfolio worldwide and focuses on developing and commercialising perovskite PV technology. In this interview, he discusses the present status and future prospects of perovskite PV. The interview is available at https://youtu.be/sbe9Z5oEs5o.

Perovskite-based optoelectronic devices are gaining much attention owing to their remarkable performance and low processing cost, particularly for solar cells. However, for perovskite light-emitting diodes, non-radiative charge recombination has limited the electroluminescence efficiency. Here we demonstrate perovskite-polymer bulk heterostructure light-emitting diodes exhibiting external quantum efficiencies of up to 20.1% (at current densities of 0.1-1 mA cm(-2)). The light-emitting diode emissive layer comprises quasi-two-dimensional and three-dimensional (2D/3D) perovskites and an insulating polymer. Photogenerated excitations migrate from quasi-2D to lower-energy sites within 1 ps, followed by radiative bimolecular recombination in the 3D regions. From near-unity external photoluminescence quantum efficiencies and transient kinetics of the emissive layer with and without charge-transport contacts, we find non-radiative recombination pathways to be effectively eliminated, consistent with optical models giving near 100% internal quantum efficiencies. Although the device brightness and stability (T-50 = 46 h in air at peak external quantum efficiency) require further improvement, our results indicate the significant potential of perovskite-based photon sources. Funding Agencies|Cambridge Trust; China Scholarship Council; VINNMER Marie-Curie Fellowship; Royal Society Newton-Bhabha International Fellowship; UAEs Distinguished Student Scholarship Program; UAEs Ministry of Presidential Affairs; Engineering and Physical Sciences Research Council (EPSRC); Thousand Talent Program; EPSRC; European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programme [670405]

Perovskite-based photovoltaics are an emerging solar technology with lab scale device efficiencies of over 22 %, and significant steps are being made toward their commercialization. Conventionally high efficiency perovskite solar cells are formed from high boiling point, polar aprotic solvent solutions. Methylammonium lead iodide (CH3NH3PbI3) films can be made from a range of solvents and blends; however, the role the solvent system plays in determining the properties of the resulting perovskite films is poorly understood. Acetonitrile (ACN), in the presence of methylamine (MA), is a viable nontoxic solvent for fabrication of CH3NH3PbI3 photovoltaic devices with efficiencies >18 %. Herein we examine films prepared from ACN/MA and dimethylformamide (DMF) and scrutinize their physical and electronic properties using spectroscopy, scanning probe imaging, and ion scattering. Significant differences are observed in the chemistry and electronic structure of CH3NH3PbI3 films made with each solvent, ACN/MA produces films with superior properties resulting in more efficient photovoltaic devices. Here we present a holistic and complete understanding of a high performance perovskite material from an electronic, physical, and structural perspective and establish a robust toolkit with which to understand and optimize photovoltaic perovskites.

Thin (approximately 10 nm) oxide buffer layers grown over lead-halide perovskite device stacks are critical for protecting the perovskite against mechanical and environmental damage. However, the limited perovskite stability restricts the processing methods and temperatures (=180 ��C to be used to coat the perovskite. This is >=70 ��C higher than achievable by current methods and results in more conductive TiOx films, boosting solar cell efficiencies by >2%. Likewise, when AP-CVD SnOx (x ~ 2) is grown on perovskites, there is also minimal damage to the perovskite beneath. The SnOx layer is pinhole-free and conformal, which reduces shunting in devices, and increases steady-state efficiencies from 16.5% (no SnOx) to 19.4% (60 nm SnOx), with fill factors reaching 84%. This work shows AP-CVD to be a versatile technique for growing oxides on thermally-sensitive materials., R.D.R and R.A.J contributed equally. 23 pages. 6 figures

The production of highly efficient single‐ and multijunction metal halide perovskite (MHP) solar cells requires careful optimization of the optical and electrical properties of these devices. Here, precise control of CH3NH3PbI3 perovskite layers is demonstrated in solar cell devices through the use of dual source coevaporation. Light absorption and device performance are tracked for incorporated MHP films ranging from ≈67 nm to ≈1.4 µm thickness and transfer‐matrix optical modeling is utilized to quantify optical losses that arise from interference effects. Based on these results, a device with 19.2% steady‐state power conversion efficiency is achieved through incorporation of a perovskite film with near‐optimum predicted thickness (≈709 nm). Significantly, a clear signature of photon reabsorption is observed in perovskite films that have the same thickness (≈709 nm) as in the optimized device. Despite the positive effect of photon recycling associated with photon reabsorption, devices with thicker (>750 nm) MHP layers exhibit poor performance owing to competing nonradiative charge recombination in a “dead‐volume” of MHP. Overall, these findings demonstrate the need for fine control over MHP thickness to achieve the highest efficiency cells, and accurate consideration of photon reabsorption, optical interference, and charge transport properties.

The relationship between the chemical composition of lead halide perovskite materials and their crystal and electronic structure is not yet sufficiently understood, despite its fundamental importance. Here, we determine the crystal and electronic structure of cesium lead bromide (CsPbBr3) while deliberately varying the cesium content. At substoichiometric concentrations of cesium, there are large variations in the frontier electronic structure of CsPbBr3 with only small variations in Cs content. We observe a critical point after which large variations in the chemical composition of CsPbBr3 result in comparably small changes in valence and conduction band energies. This behavior is starkly different from that of traditional semiconductors, such as InGaAs and GaInP, and demonstrates an impressive energetic tolerance of CsPbBr3 to large changes in its stoichiometry. This observation helps us to understand why a broad range of relatively uncontrolled, simple processing methodologies can deliver highly functional metal halide perovskite thin films.

Amorphous TiO2 and SnO2 electron transport layers (ETLs) were deposited by low-temperature atomic layer deposition (ALD). Surface morphology and x-ray photoelectron spectroscopy (XPS) indicate uniform and pinhole free coverage of these ALD hole blocking layers. Both mesoporous and planar perovskite solar cells were fabricated based on these thin films with aperture areas of 1.04 cm2 for TiO2 and 0.09 cm2 and 0.70 cm2 for SnO2. The resulting cell performance of 18.3 % power conversion efficiency (PCE) using planar SnO2 on 0.09 cm2 and 15.3 % PCE using mesoporous TiO2 on 1.04 cm2 active areas are discussed in conjunction with the significance of growth parameters and ETL composition.

Solar cells based on metal halide perovskites continue to approach their theoretical performance limits thanks to worldwide research efforts. Mastering the materials properties and addressing stability may allow this technology to bring profound transformations to the electric power generation industry.

Metal-halide perovskite-based tandem solar cells show great promise for overcoming the Shockley–Queisser single-junction efficiency limit via low-cost tandem structures, but so far, they employ conventional bottom-cell materials that require stringent processing conditions. Meanwhile, difficulty in achieving low-bandgap ( 11% absolute gain) to the ultimate efficiency via photon recycling. We report an initial experimental demonstration of a solution-processed monolithic perovskite/CQD tandem solar cell, showin...

Despite fast development of hybrid perovskite solar cells, there are many fundamental questions related to the perovskite film which remain open. For example, there are contradicting theoretical reports on the role of the organic methylammonium cation (CH3 NH3+ ) in the methylammonium lead triiodide (CH3 NH3 PbI3 ) perovskite film. From one side it is reported that the organic cation does not contribute to electronic structure of the CH3 NH3 PbI3 film. From the other side, valence band maximum fluctuations, dependent on the CH3 NH3+ rotation, have been theoretically predicted. The resonant X-ray photoelectron spectroscopy results reported here show experimental evidence of nitrogen contribution to the CH3 NH3 PbI3 electronic structure. Moreover, the observed strong resonances of nitrogen with the I 5s and the Pb 5d-6s levels indicate that the CH3 NH3 PbI3 valence band is extended up to ≈18 eV below the Fermi energy, and therefore one should also consider these shallow core levels while modeling its electronic structure.

Perovskite thin-film solar cells are one of the most promising emerging renewable energy technologies because of their potential for low-cost, large-area fabrication combined with high energy conversion efficiencies. Recently, formamidinium lead triiodide (FAPbI3) and other formamidinium (CH(NH2)2) based perovskites have been explored as interesting alternatives to methylammonium lead triiodide (MAPbI3) because they exhibit better thermal stability. However, at present a major challenge is the scale-up of perovskite solar cells from small test-cells to full solar modules. We show that coevaporation is a scalable method for the deposition of homogeneous FAPbI3 thin films over large areas. The method allows precise control over film thickness and results in highly uniform, pinhole-free layers. Our films exhibited a high charge-carrier mobility of 26 cm2 V–1s–1, excellent optical properties, and a bimolecular recombination constant of 7 × 10–11 cm3 s–1. Solar cells fabricated using these vapor-deposited layers within a regular device architecture produced stabilized power conversion efficiencies of up to 14.2%. Thus, we demonstrate that efficient FAPbI3 solar cells can be vapor-deposited, which opens up a pathway toward large-area stable perovskite photovoltaics.

An ultrathin Al2O3 film deposited on methylammonium lead triiodide (CH3NH3PbI3) perovskite has the capability to suppress the carrier recombination process and improve the perovskite solar cells efficiency and stability. However, annealing at temperatures higher than 85 °C degrades the CH3NH3PbI3 perovskite film. The X-ray photoelectron spectroscopy study performed in this work indicates that it is possible to grow Al2O3 by atomic layer deposition on the perovskite at room temperature, however, besides pure Al2O3 some OH groups are found and the creation of lead and iodine oxides at the Al2O3/CH3NH3PbI3 interface takes place.

Metal halide perovskites are generating enormous excitement for use in solar cells and light-emission applications, but devices still show substantial non-radiative losses. Here, we show that by combining light and atmospheric treatments, we can increase the internal luminescence quantum efficiencies of polycrystalline perovskite films from 1% to 89%, with carrier lifetimes of 32 μs and diffusion lengths of 77 μm, comparable with perovskite single crystals. Remarkably, the surface recombination velocity of holes in the treated films is 0.4 cm/s, approaching the values for fully passivated crystalline silicon, which has the lowest values for any semiconductor to date. The enhancements translate to solar cell power-conversion efficiencies of 19.2%, with a near-instant rise to stabilized power output, consistent with suppression of ion migration. We propose a mechanism in which light creates superoxide species from oxygen that remove shallow surface states. The work reveals an industrially scalable post-treatment capable of producing state-of-the-art semiconducting films. Metal halide perovskites are exciting materials for low-cost optoelectronic devices such as solar cells and LEDs. In order to reach the theoretical efficiency limits for both applications, any parasitic non-radiative charge-carrier recombination losses, such as those mediated by carrier trapping, must be eliminated. At present, perovskite materials still suffer from substantial non-radiative decay, particularly under solar illumination conditions, and are therefore yet to reach their full potential. Perovskite single crystals have very low trap concentrations but their controlled growth into devices does not lend themselves to the advantages offered by solution-processing thin films such as roll-to-roll depositions. Here, we demonstrate the use of light and atmospheric treatments on polycrystalline perovskite films, resulting in minimal non-radiative losses and properties approaching those of perovskite single crystals and even the best crystalline semiconductors reported to date. The authors demonstrate the use of light and atmospheric treatments on polycrystalline perovskite thin films, resulting in properties approaching those of the best crystalline semiconductors reported to date. The results translate to exceptional photovoltaic device performances with rapid rises to stabilized power output consistent with an inhibition of ionic migration.

During the past year, halide double perovskites attracted attention as potential lead-free alternatives to Pb-based halide perovskites. However, none of the compounds discovered so far can match the optoelectronic properties of MAPbI3 (MA = CH3NH3). Here we argue that, from the electronic structure viewpoint, the only option to make Pb-free double perovskites retaining the remarkable properties of MAPbI3 is to combine In and Bi as B(+) and B(3+) cations, respectively. While inorganic double perovskites such as Cs2InBiX6 were found to be unstable due to In(+) oxidizing into In(3+), we show that the +1 oxidation state of In becomes progressively more stable as the A-site cation changes from K to Cs. Hence, we propose the use of MA and FA [FA = CH(NH2)2] to stabilize A2InBiBr6 double perovskites. We show that the optoelectronic properties of A2InBiBr6 are remarkably similar to those of MAPbI3, and explore the mixed-cation (Cs/MA/FA)2InBiBr6 halide double perovskites.

Perovskite solar cells are considered a promising technology for solar-energy conversion, with power conversion efficiencies currently exceeding 20 %. In most of the reported devices, Spiro-OMeTAD is used for positive-charge extraction and transport layer. Although a number of alternative hole-transporting materials with different aromatic or heteroaromatic fragments have already been synthesized, a cheap and well-performing hole-transporting material is still in high demand. In this work, a two-step synthesis of a carbazole-based hole-transporting material is presented. Synthesized compounds exhibited amorphous nature, good solubility and thermal stability. The perovskite solar cells employing the newly synthesized material generated a power conversion efficiency of 16.5 % which is slightly lower than that obtained with Spiro-OMeTAD (17.5 %). The low-cost synthesis and high performance makes our hole-transport material promising for applications in perovskite-based optoelectronic devices.

A simple carbazole-based conjugated enamine V950 was synthesized, fully characterized and incorporated into a perovskite solar cell, which displayed high power conversion efficiency close to 18%. The investigated hole transporting material was synthesized via an extremely simple route (one step, no expensive catalysts, no column chromatography or sublimation purification) from commercially available and relatively inexpensive starting reagents, resulting in more than one order of magnitude lower cost of the final product compared to the commercial 2,2′,7,7′-tetrakis(N,N-di-p-methoxy-phenylamine)-9-9′-spirobifluorene (spiro-OMeTAD). This material promises to be a viable p-type organic charge conductor to be employed in the scale-up and manufacturing of perovskite solar modules.

Organo-lead-halide perovskite based solar cells have achieved remarkable advancements in power conversion efficiencies (PCEs) in recent years. Given their attractive properties, possible applications for perovskites are wide ranging and among others, particularly appealing for building integrated photovoltaics (BIPVs). In this study, patterned perovskite films were successfully fabricated based on a microsphere lithography SiO2 honeycomb scaffold template, which was derived by a combination of air-water interface self-assembly and O2 plasma etching. These patterned perovskite films exhibited near-neutral-color and tunable semitransparency, which meet the requisites of semitransparent solar cells for BIPVs application. O2 plasma etching of the microsphere template could effectively improve the active layer average visible transmission (AVT), and the existence of the SiO2 nanoscaffold effectively smoothed the internal trade-off of active layer AVT and device PCE. Solar cell devices fabricated with these optimized patterened perovskite films yielded a maximum PCE of 10.3% with relatively high active layer AVT of 38%. This nanoscaffold patterned perovskite opens up a new strategy for design and fabrication of functional photoelectric device based on organo-lead-halide perovskite.

Since the first reports of efficient organic–inorganic perovskite solar cells in 2012, an explosion of research activity has emerged around the world, which has led to a rise in the power conversion efficiencies (PCEs) to over 20%. Despite the impressive efficiency, a key area of the device which remains suboptimal is the electron extraction layer and its interface with the photoactive perovskite. Here, we implement an electron collection “bilayer” composed of a thin layer of zirconia coated with titania, sitting upon the transparent conductive oxide fluorine-doped tin oxide (FTO). With this double collection layer we have reached up to 17.9% power conversion efficiency, delivering a stabilized power output (SPO) of 17.0%, measured under simulated AM 1.5 sunlight of 100 mW cm–2 irradiance. Finally, we propose a mechanism of the charge transfer processes within the fabricated architectures in order to explain the obtained performance of the devices.

Metal halide perovskite absorber materials have emerged as a potential new technology for large-scale low-cost photovoltaic solar power. One great advantage lies in the ability to tune their light absorption band across the visible to near infrared spectral regions, making it an ideal candidate for tandem solar cell applications, in combination with traditional crystalline silicon. For a multi-junction solar cell to operate at peak efficiency, the current generation in all junctions must closely match, especially for monolithically integrated tandem architectures. It is feasible to achieve such matching under a standardized solar spectrum with direct illumination. However, under real world conditions the spectrum of sun light, and the fraction of diffuse to direct sun light varies considerably depending upon the location and weather conditions. Hence, it is not directly obvious how much more efficient a multi-junction solar cell needs to be, in comparison to a single junction cell, before it will produce more electrical power under real world conditions. Here, we introduce a rigorous optical and device simulation to optimize perovskite-on-silicon tandem solar cells and identify feasibility of various optimisation parameters to achieve the highest possible efficiencies. Firstly, we determine that the ideal bandgap for a perovskite “top-cell” is 1.65 eV, which will deliver up to 32% efficiency when combined with a silicon rear cell. Furthermore, we calculate the annual energy yield under hourly spectrum changes at different locations and optimize the stack to show that tandem solar cells are yielding up to 30% more energy output than the single junction silicon. Most critically, the standardized air mass 1.5 efficiency measurement improvements observed for the tandems cells, translate almost entirely to the same fractional improvement in energy yield. Hence, the efficiency of the tandem cell is not significantly “de-rated” by real world spectral variations. We do observe however, that tandem solar cell stacks can deliver further improvements by optimising differently depending on the location of installation. Our results justify the drive towards monolithically integrated multi-junction solar cells, and will enable guidance to design the ideal perovskite tandem device and allow estimations for energy yield and hence the levelized cost of electricity.