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Large area metal halide perovskite LEDs were fabricated by inkjet printing. Homogeneous drying and crystallization was facilitated by a guided and optimized gas flow.

Both nanosecond pulses and picosecond laser pulses are used for P2 patterning of chalcopyrite (Cu(In,Ga)Se2, CIGSe) and metal halide perovskite solar cell absorber layers. For CIGSe, the range of the modified material visualized by photoluminescence imaging is significantly wider than the actual physical linewidth, since energy input by the laser pulses leads to material modification in the vicinity of the scribed lines. This effect does not occur with the perovskite absorber layers, where there is no apparent influence on the edge regions. From numerical calculations of the temperature depth-profiles and the surface temperature distributions it is concluded that this effect is due to the significantly lower perovskite absorber layer thickness compared to CIGSe and the nevertheless significantly higher laser fluence required for perovskite ablation. The unaffected edge regions around the P2 line in the perovskite enabled a reduction of the dead area width in the fabrication of 3-segmented mini-modules, which could be significantly reduced from 430 to 230 µm, while increasing the aperture area power conversion efficiency and also the geometric fill factor, which could be increased up to 94.6%.

The interest in metal halide perovskites has grown as impressive results have been shown in solar cells, light emitting devices, and scintillators, but this class of materials have a complex crystal structure that is only partially understood. In particular, the dynamics of the nanoscale ferroelastic domains in metal halide perovskites remains difficult to study. An ideal in situ imaging method for ferroelastic domains requires a challenging combination of high spatial resolution and long penetration depth. Here, we demonstrate in situ temperature-dependent imaging of ferroelastic domains in a single nanowire of metal halide perovskite, CsPbBr3. Scanning X-ray diffraction with a 60 nm beam was used to retrieve local structural properties for temperatures up to 140 °C. We observed a single Bragg peak at room temperature, but at 80 °C, four new Bragg peaks appeared, originating in different real-space domains. The domains were arranged in periodic stripes in the center and with a hatched pattern close to the edges. Reciprocal space mapping at 80 °C was used to quantify the local strain and lattice tilts, revealing the ferroelastic nature of the domains. The domains display a partial stability to further temperature changes. Our results show the dynamics of nanoscale ferroelastic domain formation within a single-crystal perovskite nanostructure, which is important both for the fundamental understanding of these materials and for the development of perovskite-based devices.

In this work, we present a detailed investigation of the optical properties of hybrid perovskite building blocks, [PbI2+n]n−, that form in solutions of CH3NH3PbI3 and PbI2. The absorbance, photoluminescence (PL) and photoluminescence excitation (PLE) spectra of CH3NH3PbI3 and PbI2 solutions were measured in various solvents and a broad concentration range. Both CH3NH3PbI3 and PbI2 solutions exhibit absorption features attributed to [PbI3]1− and [PbI4]2− complexes. Therefore, we propose a new mechanism for the formation of polymeric polyiodide plumbates in solutions of pristine PbI2. For the first time, we show that the [PbI2+n]n− species in both solutions of CH3NH3PbI3 and PbI2 exhibit a photoluminescence peak at about 760 nm. Our findings prove that the spectroscopic properties of both CH3NH3PbI3 and PbI2 solutions are dominated by coordination complexes between Pb2+ and I−. Finally, the impact of these complexes on the properties of solid‐state perovskite semiconductors is discussed in terms of defect formation and defect tolerance., The optical properties of hybrid perovskite „building blocks” – polyiodide plumbates ([PbI2+n]n−) – formed in solutions of CH3NH3PbI3 and lead iodide are studied. This study provides a deep insight into the fundamental driving forces for [PbI2+n]n− formation in both solutions and a better understanding of the role of [PbI2+n]n− solution complexes in „defect tolerance” of hybrid perovskites.

Irradiation-induced phase segregation in mixed methylammonium halide perovskite samples such as methylammonium lead bromide-iodide, MAPb(IxBr1-x)3, is being studied intensively because it limits the efficiency of wide band gap perovskite solar cells. It has been postulated that this phenomenon depends on the intrinsic ionic (in)homogeneity in samples already induced during film formation. A deeper understanding of the MAPb(IxBr1-x)3 formation processes and the influence of the halide ratio, solvents, and the perovskite precursor composition as well as the influence of processing parameters during deposition, e.g., spin coating and annealing parameters, is still lacking. Here, we use a fiber optic-based optical in-situ setup to study the formation processes of the MAPb(IxBr1-x)3 series on a subsecond time scale during spin coating and thermal annealing. In-situ UV-vis measurements during spin coating reveal the influence of different halide ratios, x, in the precursor solution on the preferential crystallization of the phase. Pure bromide samples directly form a perovskite phase, samples with high iodide content form a solvate intermediate phase, and samples with a mixed stoichiometry between 0.1 ≤ x ≤ 0.6 form both. This leads to a heterogeneous formation process via two competing reaction pathways, that leads to a heterogeneous mixture of phases, during spin coating and rationalizes the compositional heterogeneity of mixed bromide-iodide samples even after annealing.

Laser-based fabrication of metal-halide perovskite mini-modules has recently been demonstrated using nanosecond (ns) laser pulses. However, it still suffers from high-resistance contacts due to remaining PbI2 residues at the bottom of the absorber-opening P2 scribe line. Therefore, in this study, we investigate the effect of shorter picosecond (ps) laser pulses, and thus lower heat input, on the complete removal of perovskite during P2 laser patterning to achieve low series resistances and thus improved electrical performances. Based on a systematic variation of the incident laser fluence and a comprehensive electrical, morphological and compositional analysis of the scribed area, optimal process windows for successful laser-based series interconnection are identified and evidenced by current density-voltage curves. The amount of PbI2 debris at the scribe bottom is reduced by using ps instead of ns pulses, resulting in improved j-V performance due to higher fill factor and lower series resistance. A numerical analysis of the laser-induced depth-dependent temperature profile shows that overcritical heating for both pulse durations induces explosive boiling of the excited volume, but only in the case of ns structuring the melting point of the underlying transparent oxide contact layer is exceeded. The corresponding scribed line morphology shows features of thermally-driven direct ablation (i.e., splashes), whereas ps pulses produce scribe lines with steep walls and delaminated areas, indicating a mechanical stress-assisted lift-off ablation. Accordingly, P2 laser patterning with ps pulses is recommended due to favorable morphological (steep edges) as well as composition-related (less PbI2 residues) scribe line properties.

Metal-halide perovskites have been shown to be remarkable and promising optoelectronic materials. However, despite ongoing research from multiple perspectives, some fundamental questions regarding their optoelectronic properties remain controversial. One reason is the high-variance of data collected from, often unstable, polycrystalline thin films. Here we use ordered arrays of stable, single-crystal cesium lead bromide (CsPbBr3) nanowires grown by surface-guided chemical vapor deposition to study fundamental properties of these semiconductors in a one-dimensional model system. Specifically, we uncover the origin of an unusually large size-dependent luminescence emission spectral blue-shift. Using multiple spatially resolved spectroscopy techniques, we establish that bandgap modulation causes the emission shift, and by correlation with state-of-the-art electron microscopy methods, we reveal its origin in substantial and uniform lattice rotations due to heteroepitaxial strain and lattice relaxation. Understanding strain and its effect on the optoelectronic properties of these dynamic materials, from the atomic scale up, is essential to evaluate their performance limits and fundamentals of charge carrier dynamics., Metal-halide perovskites are promising photovoltaic materials, but fundamental questions remain open due to their structural complexity. Here the authors show, by correlated microscopy and spectroscopy methods, that epitaxially induced lattice distortions drive a size dependent modulation of the bandgap in a homogeneous nanowire system.

In this work, we rationalize the chemical pathways and kinetics of the crystallization of methylammonium lead iodide hybrid perovskite. Our approach includes a combination of analysis of solvent coordination, the structure of intermediate solvate phases, and modeling evaporation rates of precursor solutions. The evolution of solution species via intermediate solvate phases and into perovskite thin films during drying was monitored by in situ grazing-incidence wide-angle X-ray scattering (GIWAXS). All studied precursor solutions exhibited the formation of intermediate solvate phases including a previously unreported GBL phase. In single-solvent solutions, crystallization kinetics are determined by the solvent evaporation rate and saturation concentration required for nucleation. In binary solvent mixtures, the evaporation rate of solutions is dominated by the most volatile solvent which leads to unequal evaporation of the components of the mixture. The structure of the intermediate phases in such systems strongly depends on the coordination strength and the availability of solvents upon nucleation. The combined approach described in this work allows predicting the kinetics and the chemical pathways of crystallization of hybrid perovskites in complex solvent mixtures. This insight is of great importance for future perovskite ink design.

In this communication, we present the phase diagram of CsPb BrxI1 amp; 8722;x 3 0 amp; 8804; x amp; 8804; 1, 300 585 K obtained by high throughput in situ GIWAXS measurements of a combinatorial thin film library. We find that all compositions convert to the cubic perovskite phase at high temperature and that the presence of bromide in the films stabilizes the metastable perovskite phases upon cool down. In accordance with recent predictions from DFT calculations, the transition temperatures monotonically decrease with increasing bromide content

Silver particle free inks display immense superiority and potential over silver nanoparticle based inks in the aspect of synthesis, flexibility and low temperature processing, which has attracted considerable research interest as an alternative for fabricating conductive structures in recent years. Although recent research on silver particle free inks has led to beneficial results, there are still some drawbacks some of the inks are chemically unstable and hence are not suitable for industrial inkjet printing process, although they have good conductivity; while others are cheap in terms of raw material costs but are complicated to make due to the complex synthetic route or using hazardous procedures, or are not compatible with inkjet printing. Therefore, it will be advantageous to develop a stable, cheap and inkjet printable silver particle free ink using a simple synthetic procedure. Alcohols are favorable solvents for silver particle free inks that can provide the ink with essential fluid properties for inkjet printing. However, they have some negative effects on the ink performance due to their physicochemical properties, which should be avoided. In this work, a simple do it yourself silver particle free ink is presented, which shows high chemical stability, low cost and good printability. The ink is formulated via a simple silver oxalate precursor route in alcohols. The fluid property, thermal property, stability and electrical performance of the inks based on different alcohols were investigated and optimized to obtain the final ink for printing on glass and flexible polyimide substrates. The printed Ag features yielded a resistivity of 15.46 amp; 956; amp; 937; cm at a sintering temperature of 180 C, which is equivalent to 10 times bulk silver. Based on a comprehensive assessment, we can offer a low cost, easy to make, reliable and highly competitive ink for flexible printed electronics

Solution processable metal halide perovskites are increasingly implemented in perovskite based light emitting diodes PeLEDs . Especially green PeLEDs based on methylammonium lead bromide MAPbBr3 composites exhibit impressive optoelectronic properties, while allowing processing by low cost and upscalable printing methods. In this study, we have investigated the influence of potassium chloride KCl blended into the common hole injection material poly 3,4 ethylenedioxythiophene polystyrene sulfonate PEDOT PSS to boost PeLED device performance. The inclusion of KCl firstly results in a change in morphology of the PEDOT PSS layer, which then acts as a template during deposition of the perovskite layer. A MAPbBr3 polyethylene glycol PEG composite was used, which does not require the deposition of an anti solvent droplet to induce preferential perovskite crystallization and is therefore suitable for spin coating and scalable inkjet printing processes. PeLEDs utilizing the KCl induced templating effect on a planar PEDOT PSS MAPbBr3 PEG architecture show improved performance, predominantly due to improved crystallization. PeLEDs incorporating spin coated perovskite layers yield a 40 fold increase in luminance 8000 cd m 2 while the turn on voltage decreases to 2.5 V. KCl modified PEDOT PSS contact layers enabled the realization of inkjet printed PeLEDs with luminance increased by a factor of 20 at a maximum of 4000 cd m 2 and a turn on voltage of 2.5 V. This work paves the way for inkjet printed perovskite light emitting devices for a wide variety of low cost and customizable applications

P3 patterning with ns and ps laser pulses for monolithic series interconnection of perovskite solar cells was systematically investigated. The use of ns laser pulses generates a larger amount of PbI2 and a Br-rich interface layer in the processed area, which proved to be beneficial for P3 patterning due to improved defect passivation. Thus, the P3 step should be carried out with ns laser pulses for an optimized separation of adjacent cells, while ps laser pulses were recommended for the P2 interconnect. Accordingly, suitable laser parameters for optimal laser patterning are demonstrated and novel insights into the controversial issue about the influence of PbI2 on the overall photovoltaic performance of perovskite solar cells are presented.

Perovskite and CIGSe are suitable partners for tandem solar cells, since the bandgap energies of both materials can be precisely adjusted. The fabrication of series-interconnected CIGSe-perovskite tandem solar cells requires a re-design of the series interconnection scheme for single junction cells and the development of the corresponding laser parameters for patterning. In this contribution, we present such a concept based on the evolution of the standard P1-P3 patterning design to a four-scribe line scheme by adding an additional isolation-cut (iso-cut) to separate the conductive intermediate window layer stack. To realize this interconnection scheme, laser-based processes for each individual patterning step were developed and suitable process windows were identified and evaluated.

Ferroelectric and ferroelastic domains have been predicted to enhance metal halide perovskite (MHP) solar cell performance. While the formation of such domains can be modified by temperature, pressure, or strain, established methods lack spatial control at the level of single domains. Here, we induce the formation of ferroelastic domains in CsPbBr3 nanowires at room temperature using an atomic force microscope (AFM) tip and visualize the domains using nanofocused x-ray diffraction with a 60 nm beam. Regions scanned with a low AFM tip force show orthorhombic 004 reflections along the nanowire axis, while regions exposed to higher forces exhibit 220 reflections. The applied stress locally changes the crystal structure, leading to lattice tilts that define ferroelastic domains, which spread spatially and terminate at {112}-type domain walls. The ability to induce individual ferroelastic domains within MHPs using AFM gives new possibilities for device design and fundamental experimental studies.

Fundmental comprehension of light-induced processes in perovskites are still scarce. One active debate surrounds the influence of excess lead iodide (PbI2) on device performance, as well as optoelectronic properties, where both beneficial and detrimental traits have been reported. Here, we study its impact on charge carrier recombination kinetics by simultaneously acquiring the photoluminescence quantum yield and time-resolved photoluminescence as a function of excitation wavelength (450-780 nm). The presence of PbI2 in the perovskite film is identified via a unique spectroscopic signature in the PLQY spectrum. Probing the recombination in the presence and absence of this signature, we detect a radiative bimolecular recombination mechanism induced by PbI2. Spatially resolving the photoluminescence, we determine that this radiative process occurs in a small volume at the PbI2/perovskite interface, which is only active when charge carriers are generated in PbI2, and therefore provide deeper insight into how excess PbI2 may improve the properties of perovskite-based devices.

Through the optimization of the perovskite precursor composition and interfaces to selective contacts, we achieved a p i n type perovskite solar cell PSC with a 22.3 power conversion efficiency PCE . This is a new performance record for a PSC with an absorber bandgap of 1.63 eV. We demonstrate that the high device performance originates from a synergy between 1 an improved perovskite absorber quality when introducing formamidinium chloride FACl as an additive in the triple cation Cs0.05FA0.79MA0.16PbBr0.51I2.49 Cs MAFA perovskite precursor ink, 2 an increased open circuit voltage, VOC, due to reduced recombination losses when using a lithium fluoride LiF interfacial buffer layer, and 3 high quality hole selective contacts with a self assembled monolayer SAM of [2 9H carbazol 9 yl ethyl]phosphonic acid 2PACz on ITO electrodes. While all devices exhibit a high performance after fabrication, as determined from current density voltage, J V, measurements, substantial differences in device performance become apparent when considering longer term stability data. A reduced long term stability of devices with the introduction of a LiF interlayer is compensated for by using FACl as an additive in the metal halide perovskite thin film deposition. Optimized devices maintained about 80 of the initial average PCE during maximum power point MPP tracking for gt;700 h. We scaled the optimized device architecture to larger areas and achieved fully laser patterned series interconnected mini modules with a PCE of 19.4 for a 2.2 cm2 active area. A robust device architecture and reproducible deposition methods are fundamental for high performance and stable large area single junction and tandem modules based on PSCs

Emerging photovoltaics (PVs), focuses on a variety of applications complementing large scale electricity generation. For instance, organic, dye-sensitized and some perovskite solar cells are considered in building integration, greenhouses, wearable and indoors, 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 over the state-of-the-art performance for these systems and applications. Two important resources for record 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 (STEY) is included as an analysis parameter among state-of-the-art emerging PVs.

Controlling the nucleation and crystal growth in solution-processed metal halide perovskite (MHP) thin films is the pivotal point in fabricating homogenous and pinhole-free films. Using scalable coating and printing techniques, vacuum and gas flow-assisted drying processes turn out to be the most promising methods to induce nucleation and crystallization. Yet, the exact interplay and nature of these processes are unclear. In our work, we optically monitor these processes in situ. For the first time, we can show that a controlled venting of the vacuum chamber and the use of a subsequent gas flow are key to achieve homogenous nucleation. Utilizing this gas flow-assisted vacuum drying process, we find that regular, optically dense and pinhole-free MHP layers can be fabricated via inkjet printing, which yield solar cells with a power conversion efficiency of 16%, as compared to 4.5% for vacuum drying.

The upscaling of perovskite solar cells to modules requires the patterning of the layer stack in individual cells that are monolithically interconnected in series. This interconnection scheme is composed of three lines, P1–P3, which are scribed using a pulsed laser beam. The P3 scribe is intended to isolate the back contact layer of neighboring cells, but is often affected by undesired effects such as back contact delamination, flaking, and poor electrical isolation. Herein, the influence of the laser pulse duration on the electrical and compositional properties of P3 scribe lines is investigated. The results show that both nanosecond and picosecond laser pulses are suitable for P3 patterning, with the nanosecond pulses leading to a higher open circuit voltage, a higher fill factor, and a higher power conversion efficiency. It is found that the longer pulse duration resultes in a larger amount of PbI2 formed within the P3 line and a thin Br-rich interfacial layer which both effectively passivate defects at the scribe line edges and block charge carrier in its vicinity. Thus, nanosecond laser pulses are preferable for P3 patterning as they promote the formation of beneficial chemical phases, resulting in an improved photovoltaic performance. (Less)

Environmental gains of electric cars can be optimized with the use of lightweight and recyclable magnesium in the vehicle’s structural components. Ductility improvement of low-density Mg-Al alloys will extend their use in automotive body applications. The authors achieved 63% ductility improvement in Mg-6wt%Al with trace Y (1.5 ppm) due to the β-phase refinement and predicted that higher levels would not perform as well. As predicted, 0.3wt% of Y addition investigated in this study led to lower mechanical performance and β-phase refinement than those obtained with trace additions. The tensile ductility and yield strength increased by ~13% and 16%, respectively, and the compression strain to fracture by ~22%. Scanning electron and optical microscopy, X-Rays diffraction, mechanical testing and thermodynamic calculations were used to investigate the effect of 0.3wt% Y on the microstructure of Mg-6wt%Al. The matrix dissolution revealed the close association of the Al2Y and the β-Mg17Al12 phases.

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.

Metal halide perovskites (MHP), as used in photovoltaic (PV) applications, show a rich photophysics in inert and ambient atmosphere. The presence of atmospheric molecules leads to processes that enhance as well as reduce their photoluminescence (PL) emission. Various phenomena are previously described for a wide variety of gas molecules and different classes of MHP, with a particular interest on the long-term stability for PV applications. However, reversible PL quenching (PLQ) processes, which may be regarded equally important for the performance of PV and other optoelectronic applications, are neglected in other studies. This holds true for O2 and H2O, but especially for low-reactive gases such as nitrogen and argon. Using low excitation densities, it is shown that noticeable—and reversible—PLQ, in addition to PL enhancements, can already be observed for O2, N2, and Ar as well as for H2O at low concentrations of 1 mbar. The nature and origin of the quenching processes are further elucidated by applying the Stern–Volmer analysis, also employed to determine whether static and dynamic PLQ processes happen for the different quenching gases. The strongest static PLQ is found for O2 and H2O. MHPs in N2 and Ar atmospheres display a moderate PLQ effect. (Less)

Metal halide perovskites show great promise for a wide range of optoelectronic applications but are plagued by instability when exposed to air and light. This work presents low-temperature solution growth of vertically aligned CsPbBr3 nanowire arrays in AAO (anodized aluminum oxide) templates with excellent stability, with samples exposed to air for 4 months still exhibiting comparable photoluminescence and UV stability to fresh samples. The single-crystal nanowire length is adjusted from ∼100 nm to 5 μm by adjusting the precursor solution amount and concentration, and we observe length-to-diameter ratios as high as 100. Structural characterization results indicate that large-diameter CsPbBr3 nanowires have an orthorhombic structure, while the 10 nm- and 20 nm-diameter nanowires adopt a cubic structure. Photoluminescence shows a gradual blue-shift in emission with decreasing nanowire diameter and marginal changes under varying illumination power intensity. The CsPbBr3-nanowires/AAO composite exhibits excellent resistance to X-ray radiation and long-term air storage, which makes it promising for future optoelectronic applications such as X-ray scintillators. These results show how physical confinement in AAO can be used to realize CsPbBr3 nanowire arrays and control their morphology and crystal structure.

Halide perovskites are crystalline semiconductors gaining increasing attention as low-cost, high-performance materials for optoelectronics. Their processing from solution at low temperatures is compatible with rapid manufacturing of thin-film devices, including solar cells and light-emitting diodes. Therefore, understanding the coordination chemistry in metal halide perovskite precursor solutions would allow controlling the crystallization of thin films, their material properties and device performance. Here, we present a direct nanostructural technique to characterize the colloidal structure of perovskites in precursor solutions. Small-angle scattering is particularly adept for measuring nanoparticles in solution. Applying this technique to perovskite precursor solutions, we can study their colloidal properties. We show that not only do the colloids themselves matter, but also we can reveal their strong interactions in the early stages of crystallization. In particular, we focus on the prearrangement of particles into cluster-like formations. As an example, we present the concentration dependence, which is additionally supported using 207Pb NMR.

Metal halide perovskites are the first solution processed semiconductors that can compete in their functionality with conventional semiconductors, such as silicon. Over the past several years, perovskite semiconductors have reported breakthroughs in various optoelectronic devices, such as solar cells, photodetectors, light emitting and memory devices, and so on. Until now, perovskite semiconductors face challenges regarding their stability, reproducibility, and toxicity. In this Roadmap, we combine the expertise of chemistry, physics, and device engineering from leading experts in the perovskite research community to focus on the fundamental material properties, the fabrication methods, characterization and photophysical properties, perovskite devices, and current challenges in this field. We develop a comprehensive overview of the current state-of-the-art and offer readers an informed perspective of where this field is heading and what challenges we have to overcome to get to successful commercialization. published

Record performance Metal-Halide Perovskite (MHP) based solar cells have been achieved by incremental optimization of deposition procedures based on spin-coating. We here provide unprecedented insight into the formation process of MHP thin films of the “triple cation” (Cs,MA,FA)Pb(Br,I)3 perovskite from multi-modal in-situ optical process monitoring during spin-coating and annealing. This report details small-footprint fiber-optics based optical spectroscopy setup that enables monitoring of thin-film formation processes by UV-Vis reflectance and photoluminescence spectroscopy with a sub-second time resolution. Complementary information can be obtained from optical features during different stages of film formation: 1) During the first, flow regime dominated, stage of spin-coating, the wet-film thinning can be analyzed from UV-Vis interference, 2) the onset of bulk perovskite formation is clearly observed from the evolution of the semiconductor absorption edge, and 3) Photoluminescence (PL) measurements provide complementary information on nucleation and growth processes. We here provide a comprehensive picture that rationalizes the conditions to obtain a high quality “triple cation” perovskite thin-film during spin-coating and subsequent annealing.

We prepared triplet-triplet annihilation photon upconverters combining thin-film methylammonium lead iodide (MAPI) perovskite with a rubrene annihilator in a bilayer structure. Excitation of the perovskite film leads to delayed, upconverted photoluminescence emitted from the annihilator layer, with triplet excitation of the rubrene being driven by carriers excited in the perovskite layer. To better understand the connections between the semiconductor properties of the perovskite film and the upconversion efficiency, we deliberately varied the perovskite film properties by modifying two spin-coating conditions, namely, the choice of antisolvent and the antisolvent dripping time, and then studied the resulting photon upconversion performance with a standard annihilator layer. A stronger upconversion effect was exhibited when the perovskite films displayed brighter and more uniform photoluminescence. Both properties were sensitive to the antisolvent dripping time and were maximized for a dripping time of 20 s (measured relative to the end of the spin-coating program). Surprisingly, the choice of antisolvent had a significant effect on the upconversion performance, with anisole-treated films yielding on average a tenfold increase in upconversion intensity compared to the chlorobenzene-treated equivalent. This performance difference was correlated with the carrier lifetime in the perovskite film, which was 52 ns and 306 ns in the brightest chlorobenzene and anisole-treated films, respectively. Since the bulk properties of the anisole- and chlorobenzene-treated films were virtually identical, we concluded that differences in the defect density at the MAPI/rubrene interface, linked to the choice of antisolvent, must be responsible for the differing upconversion performance.

Irradiation-induced phase segregation in mixed methylammonium halide perovskite samples such as methylammonium lead bromide-iodide, MAPb(I

Photoinduced phase separation, which limits the available band gap energies for photovoltaic applications, was reported for a range of mixed-halide perovskites. A microscopic understanding of the phase separation mechanism is still lacking but may be beneficial to rationalize limitations as well as enable the design of phase-stable perovskite semiconductors. In this letter, electron-beam-induced phase separations and transformations were investigated in a small crystallite of CsPb(Br0.8I0.2)3 by means of in situ high-resolution imaging in a transmission electron microscope. The acquired time series was evaluated using principal and independent component analysis to classify the structural change during the illumination by the electron beam. A more iodine-rich phase with the approximate composition of CsPb(Br0.6I0.4)3 was found to form at the edges of the particle, while a ternary pure bromide phase of CsPbBr3 remained at its center. These results provide an atomistic picture of in-grain phase segregation into iodide-rich phases at grain boundaries and bromide-rich phases in the interior of the grain.

Nonradiative losses in semiconductors are related to defects. At cryogenic temperatures, defect-related photoluminescence (PL) at energies lower than the band-edge PL is observed in methylammonium lead triiodide perovskite. We applied multispectral PL imaging to samples prepared by two different procedures and exhibiting 1 order of magnitude different PL quantum yield (PLQY). The high-PLQY sample showed concentration of the emitting defect sites around 10

This paper focuses on the development of 2-terminal CIGS-perovskite tandem solar cells by exploring a range of stack sequences and synthetic procedures for depositing the associated layers. In the end, we converged at a stack sequence composed of SLG/Mo/CIGS/CdS/i-ZnO/ZnO:Al/NiO/PTAA/Perovskite/LiF/PCBM/SnO2/ITO. With this architecture, we reached performances only about 1% lower than the corresponding 4-terminal tandem cells, thus demonstrating functional interconnects between the two sub-cells while grown monolithically on top of each other. We go through the stack, layer-by-layer, discussing their deposition and the results, from which we can conclude what works, what does not work, and what potentially could work after additional modifications. The challenges for a successful 2-terminal tandem device include: how to deal with, or decrease, the surface roughness of the CIGS-stack, how to obtain uniform coverage of the layers between the CIGS and the perovskite while also obtaining a benign interface chemistry, and how to tune the band gaps of both the CIGS and the perovskite to obtain good optical matching. The investigation was based on CIGS with a power conversion efficiency around 14%, and perovskites with an efficiency around 12%, resulting in 2-terminal tandem cells with efficiencies of 15–16%. The results indicate that by using higher performing CIGS and perovskite sub-cells, it should be possible to manufacture highly efficient 2-terminal CIGS-perovskite tandem devices by using the protocols, principles, and procedures developed and discussed in this paper. (Less)

Progress in the power conversion efficiency of solar cells based on metal-halide perovskite semiconductors has been astonishing for the past years. During their development, transient effects have been observed that gave rise to an uncertainty associated with the determination of device performance from current density-voltage (J–V) measurements. This effect becomes visible in a dependence of the J–V curve on scan rate and direction, causing a J-V hysteresis due to the discrepancy between forward and reverse scan.) This hysteresis has caused debates in the research community and triggered efforts to establish reliable measurement protocols. A major difficulty is that the J–V hysteresis as a function of measurement conditions can be quite specific for the device architecture and conditions the device was subjected to prior to the measurement. In this chapter, we describe hysteresis in perovskite solar cells phenomenologically and summarize the current understanding of underlying causes. We emphasize insight that can be gained from the quantitative analysis of the magnitude of hysteresis and time scales of transient phenomena. In this context, we discuss the value and limitation of hysteresis indices as quantitative metrics in the analysis of hysteresis. We summarize how device architecture, contact layers and composition of the metal-halide perovskite absorber layer affect the magnitude of transient phenomena. In the meantime, uncertainties related to the determination of the power-conversion efficiency have been practically solved by tracking the power output. However, gaining insight into the underlying physical causes for hysteresis is crucial. This understanding will illuminate the intrinsic properties of MHP semiconductors and allow the evaluation of their technological potential also regarding long-term stability.

Solvent-solute interactions in precursor solutions of lead halide perovskites (LHP) critically impact the quality of solution-processed materials, as they lead to the formation of a variety of poly-iodoplumbates that act as building blocks for LHP. The formation of [PbI$_{2+n}$]$^{n-}$ complexes is often expected in diluted solutions while coordination occurring at high concentrations is not well understood yet. In a combined \textit{ab initio} and experimental work, we demonstrate that the optical spectra of the quasi-one-dimensional iodoplumbate complexes PbI$_2$(DMSO)$_4$, Pb$_2$I$_4$(DMSO)$_6$, and Pb$_3$I$_6$(DMSO)$_8$ formed in dimethyl sulfoxide solutions are compatible with the spectral fingerprints measured at high concentrations of lead iodide. This finding suggests that the formation of polynuclear lead-halide complexes should be accounted for in the interpretation of optical spectra of LHP precursor solutions.

The formation mechanism and the evolution of optoelectronic properties during annealing of chlorine derived methylammonium lead iodide MAPbI3 amp; 8722;xClx are investigated in detail combining in situ and ex situ optical and structural characterization. Using in situ optical reflectometry we are able to monitor the evolution of the MAPbI3 amp; 8722;xClx phase as a function of time and processing temperature. The formation kinetics is fitted using an improved Johnson Mehl Avrami Kolmogorov model and a delayed formation of MAPbI3 amp; 8722;xClx is found when chlorine is present in the precursor. This is verified by X ray diffraction and X ray fluorescence measurements. From absolute photoluminescence measurements we determine the implied Voc during film formation, which exhibits a maximum at a specific time during the annealing process. In conjunction with ex situ time resolved photoluminescence we deduce a decrease in the net doping density for increased annealing times, while the minority carrier lifetime stays constant. We thus demonstrate the potential of in situ optical spectroscopy to monitor and tailor the electronic properties of hybrid perovskites directly during film growth, which can be easily applied to different growth recipes and synthesis environments

Perovskite solar cells are among the most exciting photovoltaic systems as they combine low recombination losses, ease of fabrication, and high spectral tunability. The Achilles heel of this technology is the device stability due to the ionic nature of the perovskite crystal, rendering it highly hygroscopic, and the extensive diffusion of ions especially at increased temperatures. Herein, we demonstrate the application of a simple solution-processed perfluorinated self-assembled monolayer (p-SAM) that not only enhances the solar cell efficiency, but also improves the stability of the perovskite absorber and, in turn, the solar cell under increased temperature or humid conditions. The p-i-n-type perovskite devices employing these SAMs exhibited power conversion efficiencies surpassing 21%. Notably, the best performing devices are stable under standardized maximum power point operation at 85 °C in inert atmosphere (ISOS-L-2) for more than 250 h and exhibit superior humidity resilience, maintaining ∼95% device performance even if stored in humid air in ambient conditions over months (∼3000 h, ISOS-D-1). Our work, therefore, demonstrates a strategy towards efficient and stable perovskite solar cells with easily deposited functional interlayers.

Preparation of metal halide perovskites under room temperature attracts attention because of energy saving by removing thermal annealing. Room temperature trans formation of spin cast wet films consisting of methylammo nium MA iodide, PbI2, and dimethylformamide toward solid MAPbI3 perovskite proceeds via several intermediate crystal line states and is strongly dependent on ambient humidity. Light transmission and photoluminescence PL microscopy and spectroscopy were used to monitor the growth of crystals and transformation of their properties in time under nitrogen atmosphere at room temperature. Under low humidity, a highly luminescent intermediate phase with low absorption in the visible range appears, with the PL spectra composed of several bands in the range from 600 to 760 nm. We assign these bands to low dimensional nanocrystals and two dimensional inclusions MAPbI3 intermediates, where the exciton confinement shifts the spectrum to higher energies in comparison with the bulk MAPbI3. The intermediate levels of ambient humidity 10 amp; 8722;50 appear to catalyze the conversion of the intermediate phase to MAPbI3. At a high ambient humidity gt;80 , the initially formed MAPbI3 is quickly transformed to the transparent hydrate phase of MAPbI3. The role of ambient water catalyzing the material transformation by competing for Pb coordination with the solvent molecules is discussed