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Formamidinium lead iodide (FAPbI3) is the benchmark material for the most efficient near‐infrared perovskite light‐emitting diodes (LEDs) and a promising gain medium for perovskite‐based coherent light sources. Thus, it is crucial to understand and control its defect chemistry to harness the full potential of its exceptional radiative recombination properties. Here, this topic is addressed by tailoring the I− to Br− ratio in the perovskite composition. It is found that introducing small Br− quantities improves the yield of radiative recombination with a beneficial impact on both spontaneous and amplified spontaneous emission (ASE) and improves the semiconductor photostability leading to reduced luminescence efficiency roll‐off and enhanced radiance in LEDs. By employing photoemission electron microscopy (PEEM), this improvement in optoelectronic performance can be directly correlated to a reduced hole‐trapping activity achieved by replacing iodide with bromide, thus, providing a convenient yet powerful synthetic approach to control the defect chemistry of the material and fostering its implementation in advanced photonic platforms. [ABSTRACT FROM AUTHOR]

The two‐step sequential deposition method is considered a potential way for the large‐scale manufacture of perovskite solar cells (PSCs) with high power conversion efficiency and reproducibility. However, the dense lead iodide (PbI2) film interferes with its full contact with organic solutions, resulting in an inadequate reaction at the interface. Herein, 2 kinds of metal‐organic framework (MOF) are introduced, amorphous Ni‐MOF‐74 (amNi‐MOF‐74) and crystalline Zn‐MOF‐74 (crZn‐MOF‐74), into PbI2 for regulating crystallization. Compared to crZn‐MOF‐74, the incorporation of amNi‐MOF‐74 exhibited rapid nucleation, resulting in high‐quality perovskite films with large grain size, low trap density, and enhanced charge transfer between the perovskite and charge transfer layers. Meanwhile, the content of unstable phase PbI2 left in perovskite films due to insufficient reaction is also reduced. The amNi‐MOF‐74 modified PSCs exhibited a champion power conversion efficiency of 24.17% with good humidity and thermal stability. The unencapsulated device maintains 90% of its initial efficiency after 1000 h storage in dark ambient conditions with ≈30% relative humidity. This strategy provides an effective approach for promoting the crystallization process of perovskite and fabricating efficient and stable PSCs. [ABSTRACT FROM AUTHOR]

Continuous heat generation in perovskite solar cells (PSCs), caused by solar radiation, poses a significant challenge to their lifespan. Existing active cooling methods require extra energy input and might not be effective at high temperatures. Most reported passive radiative cooling materials either lack solar transparency or require complex fabrication processes. Here, mesoporous silica nanoparticles are designed, synthesized, and assembled into multilayered stacks with a graded refractive index (GRI) by spray coating them on top of PSCs made from methylammonium lead iodide (MAPbI3) over a large scale (15.6 × 15.6 cm2). This coating offers both high transparency in the visible wavelength and high emissivity in the mid‐infrared region, leading to an average temperature reduction of 6.65 ±  1.48 °C in GRI‐coated MAPbI3 PSCs under outdoor conditions compared to non‐coated references. After 50 d, the GRI‐coated PSCs maintain 80.9 ± 8.7% of their initial photoconversion efficiency, in contrast to 6.1 ± 5.9% for the noncoated ones. The calculated cooling power of the GRI‐coated PSCs is 28.9% higher than that of the reference cells. [ABSTRACT FROM AUTHOR]

Hybrid organometal halide perovskites (HP) present exceptional optoelectronic properties, but their poor long‐term stability is a major bottleneck for their commercialization. Herein, a solvent‐free approach to growing single‐crystal organic nanowires (ONW) is presented, along with nanoporous metal oxide scaffolds and HP, to form a core@multishell architecture. The synthesis is carried out under mild vacuum conditions employing thermal evaporation for the metal‐free phthalocyanine (H2Pc) nanowires, which are the core, plasma‐enhanced chemical vapor deposition (PECVD) for the TiO2 shell, and co‐evaporation of lead iodide (PbI2) and methylammonium iodide (CH3NH3I/MAI) for the CH3NH3PbI3 (MAPbI3/MAPI) perovskite shell. A detailed characterization of the nanostructures by electron microscopy, (S)‐TEM, and X‐ray diffraction, XRD, is presented, revealing a different crystallization of the HP depending on the template: while the growth on H2Pc nanowires induces the typical MAPI tetragonal structure, a low‐dimensional phase (LDP) is observed on the 1D‐TiO2 nanotubes. Such a combination yields an unprecedentedly stable photoluminescence emission over 20 h and over 300 h after encapsulation in polymethyl methacrylate (PMMA) under different atmospheres including N2, air, and high moisture levels. Moreover, the unique 1D morphology of the system, together with the high refractive index, allows for a strong waveguiding effect along the HP nanowire length. [ABSTRACT FROM AUTHOR]

Layered (2D) perovskites are an emerging attractive 2D system with enhanced stability to ambient conditions as opposed to their highly unstable three dimensional bulk counterpart. Their uniquely tuneable optical and electrical properties are underpinning a surge of interest in 2D‐photovoltaics. So far, the development of nano‐scale integrated opto‐electronic 2D perovskite devices remains nearly unexplored since they have generally been found to be incompatible with standard top‐down semiconductor nano‐fabrication technologies. Here, following the synthesis of solvent‐stable 2D‐fluorinated phenethylammonium lead iodide perovskite (F‐PEA)2PbI4 (F‐PEAI), planar photodetectors entirely fabricated in atmosphere is demonstrated, exhibiting figures of merit rivalling those of commercial silicon photodiodes. A record large room temperature detectivity (>5 × 1017 Jones), a fast time photoresponse (rise time 1.5 ns), an extraordinarily large linear dynamic range (228 dB), as well as a photo‐responsivity of ≈ 1100 AW−1 are demonstrated for devices on a range of substrates including flexible wearable media without the need for any planarization or any atomically thin dielectric, in stark contrast to other 2D semiconductors. Finally, the suitability of nano‐scale 2D F‐PEAI photodetector arrays with sub‐wavelength pixel size of just 100 nm of use for high definition imaging is demonstrated. [ABSTRACT FROM AUTHOR]

Pure‐phase α‐formamidinium lead iodide (α‐FAPbI3) perovskite solar cells (PSCs) possess potential high efficiency because of suitable bandgap. However, achieving high‐quality α‐FAPbI3 films during the spin‐coating process is challenging without anti‐solvent extraction, due to the spontaneous formation of the more stable δ‐FAPbI3 phase and the complexity of multi‐component perovskite precursor solutions. Here a gel precursor with an amorphous structure to eliminate the need for anti‐solvent extraction in achieving the homogeneous and highly oriented pure‐phase α‐FAPbI3 is devised films. The incorporation of N,N′‐dimethylpropyleneurea, and alkylammonium chloride results in extended iodoplumbate clusters in the perovskite precursor solution. In situ, spectroscopic analysis reveals that the emergence of the stable amorphous gel precursor during the initial solidification stage ensures a uniform solute distribution. This effectively prevents preferentially oriented growth in the crystal phase precursor, leading to a significant enhancement in film homogeneity. As a result, power conversion efficiencies of 24.17% for the PSC, and 19.3% for the module are achieved, along with superior operational stability, retaining 96.1% of their initial efficiency after 850 h at the maximum power point tracking. These demonstrate the best performance for the reported pure‐phase α‐FAPbI3 PSCs without anti‐solvent extraction, showing great promise for scalable manufacture. [ABSTRACT FROM AUTHOR]

Metal‐halide perovskites have proven to be a versatile group of semiconductors for optoelectronic applications, with ease of bandgap tuning and stability improvements enabled by halide and cation mixing. However, such compositional variations can be accompanied by significant changes in their charge‐carrier transport and recombination regimes that are still not fully understood. Here, a novel combinatorial technique is presented to disentangle such dynamic processes over a wide range of temperatures, based on transient free‐space, high‐frequency microwave conductivity and photoluminescence measurements conducted simultaneously in situ. Such measurements are used to reveal and contrast the dominant charge‐carrier recombination pathways for a range of key compositions: prototypical methylammonium lead iodide perovskite (MAPbI3), the stable mixed formamidinium‐caesium lead‐halide perovskite FA0.83Cs0.17PbBr0.6I2.4 targeted for photovoltaic tandems with silicon, and fully inorganic wide‐bandgap CsPbBr3 aimed toward light sources and X‐ray detector applications. The changes in charge‐carrier dynamics in FA0.83Cs0.17PbBr0.6I2.4 across temperatures are shown to be dominated by radiative processes, while those in MAPbI3 are governed by energetic disorder at low temperatures, low‐bandgap minority‐phase inclusions around the phase transition, and non‐radiative processes at room temperature. In contrast, CsPbBr3 exhibits significant charge‐carrier trapping at low and high temperatures, highlighting the need for improvement of material processing techniques for wide‐bandgap perovskites. [ABSTRACT FROM AUTHOR]

Hybrid halide perovskite has established its credibility as high performance thin film photovoltaic technology. Perovskite based on formamidinium cation is at the core composition to top performances and stability. Herein, a depth study based on temperature‐controlled in situ X‐ray diffraction focusing on the photo‐active formamidinium lead iodide (α‐FAPbI3) is reported. In particular, the thermal stability of the latter and the degradation pathways under different experimental conditions are clarified. Based on this in situ technique, the lattice thermal expansion coefficient is reported that provides relevant information on possible mechanical stress created upon temperature cycling or damp heat test. The results support that α‐FAPbI3 degradation is substantially accelerated when temperature is combined to illumination and when it is interfaced with the extraction layers. In addition, by contrast to in darkness for which α‐FAPbI3 degrades directly into PbI2, the existence of a temperature gap under illumination involving an intermediate step with a non‐crystalline phase resulting from the perovskite degradation and contributing to the formation of PbI2 by‐product is revealed. [ABSTRACT FROM AUTHOR]

In hybrid perovskites, the organic molecules and inorganic frameworks exhibit distinct static and dynamic characteristics. Their coupling will lead to fascinating phenomena, such as large polarons, dynamic Rashba–Dresselhaus effects, etc. In this paper, deep potential molecular dynamics (DPMD) is employed, a large‐scale MD simulation scheme with DFT accuracy, to study hybrid perovskites formamidinium lead iodide (FAPbI3) and methylamonium lead iodide (MAPbI3). A spontaneous hybrid nano‐domain behavior, namely multiple molecular rotation nano‐domains embedded into a single [PbI6]4− octahedra rotation domain, is first discovered at low temperatures. The behavior originates from the interplay between the long range order of molecular rotation and local lattice deformation, and clarifies the puzzling structural features of FAPbI3 at low temperatures. The work provides new insights into the structural characteristics and stability of hybrid perovskite, as well as new ideas for the structural characterization of organic–inorganic coupled systems. [ABSTRACT FROM AUTHOR]

Wide‐bandgap (WBG) perovskite solar cells (PSCs) have garnered significant attention for their potential applications in tandem solar cells. However, their large open‐circuit voltage (VOC) deficit and serious photo‐induced halide segregation remain the main challenges that impede their applications. Herein, a post‐treatment strategy without thermal annealing is presented to form a 2D top layer of 2‐thiopheneethylammonium lead halide (n = 1) on WBG perovskites. This thermal annealing‐free post‐treatment method can more effectively passivate the defects of WBG methylamine (MA)‐free formamidinium/cesium lead iodide/bromide perovskite films and suppress photo‐induced perovskite phase segregation, as compared with the thermal annealing method that yields multi‐2D phases. The resulting opaque and semi‐transparent 1.66 eV‐bandgap perovskite solar cells deliver maximum power conversion efficiencies of 21.47% (a small VOC deficit of 0.43 V) and 19.11%, respectively, both of which are among the highest reports for inverted MA‐free WBG PSCs. Consequently, four‐terminal all‐perovskite tandem cells realize a remarkable efficiency of 26.64%, showing great promise for their applications in efficient multi‐junction tandem solar cells. [ABSTRACT FROM AUTHOR]

It is widely believed that excess/residual lead iodide (PbI2) can affect the performance of perovskite solar cells. Moderate PbI2 can enhance efficiency by passivating defects, while extremely active PbI2 leads to non‐negligible hysteresis effects and reduces device stability. Although several efforts are made to investigate the role of excess PbI2, its impact is still underestimated. Recent advances further demonstrate the extraordinary potential of modifying excess PbI2; however, a comprehensive study is required to obtain a deeper understanding. Herein, the important breakthroughs regarding excess PbI2 are reviewed and the mechanism of excess PbI2 in terms of efficiency and stability is rethought. In addition, the origins, verification, and regulation of residual PbI2 are summarized. [ABSTRACT FROM AUTHOR]

The substrates of conventional flexible perovskite solar cells (FPSCs) are thermoplastic polymer material polyethylene naphthalate (PEN), which will deform during high temperature annealing process. In addition, lead iodide (PbI2) permanently formed and the substrate undergoes reversible deformation from 20 °C to 200 °C and back to 20 °C. Therefore, to balance the substrate supporting capacity and the crystalline quality of narrow band gap α‐phase formamidinium lead iodide (α‐FAPbI3), an annealing process of 120 °C for 30 minutes is determined. Additionally, there will also be a large number of gaps and lattice strain at the perovskite grain boundaries during the annealing process as the FAPbI3 phase transition is accompanied by much lattice shrinkage. As a result, 1,6‐hexanediammonium diiodide (HADI) is chosen to passivate the defects and release the stress of perovskite film. Therefore, a recorded 1.4% extended stretch rate of the flexible film is attained. Finally, the champion PCE of 21.14% under AM 1.5G and 31.52% under 1062 lux is achieved after HADI treatment, accompanied by a better long‐term and mechanical stability. This study provides annealing process optimization and stress relief strategies for the further development of narrow band gap FPSCs. [ABSTRACT FROM AUTHOR]

High density of defects at interface severely affects the performance of perovskite solar cells (PSCs). Herein, cobalt (II) hexafluoro‐2,4‐pentanedionat (CoFAc), a hinge‐type fluorine‐rich complex, is introduced onto the surface of formamidinium cesium lead iodide (FACsPbI3) film to address the issues of perovskite/Spiro‐OMeTAD interface. The existence of CoFAc passivates both organic cation and halide anion vacancies by establishing powerful hydrogen bonds with HC(NH2)2+ (FA+) and strong ionic bonds with Pb2+ in perovskite films. In addition, CoFAc serves as a connecting link to enhance interfacial hole‐transport kinetics via interacting with Spiro‐OMeTAD. Consequently, FACsPbI3 PSCs with CoFAc modification display a champion power conversion efficiency (PCE) of 24.64% with a charming open‐circuit voltage (VOC) of 1.191 V, which is the record VOC among all the reported organic‐inorganic hybrid PSCs with TiO2 as electron transport layer. Furthermore, CoFAc‐modified devices exhibit an outstanding long‐term stability, which can maintain 95% of their initial PCEs after exposure to ambient atmosphere for 1500 h without any encapsulation. [ABSTRACT FROM AUTHOR]

Metal halide perovskite microwires (MWs) have emerged as promising photoactive materials for highly efficient photodetectors (PDs). However, large‐scale MWs film fabrication is still a formidable challenge for achieving integration compatible perovskite PDs arrays, owing to precipitation and structure crushing of MWs during deposition and annealing. Herein, a strategy of fabrication of inch‐scale perovskite MWs films is presented by depositing perovskite intermediate suspension through spray‐coating, which addresses the trade‐off present between the high flatness of MWs film and its large‐scale fabrication. The single crystalline perovskite MWs weave a film with high enough flatness rendering narrow performance distribution of high efficiency on the 7 × 7 PDs arrays. The formamidinium lead iodide (FAPbI3) PDs arrays show average responsivity and detectivity of (1.60 ± 0.46) A W−1 and (1.49 ± 0.50) × 1012 Jones. The methanaminium lead iodide (MAPbI3) PDs arrays show average responsivity and detectivity of (0.065 ± 0.046) A W−1 and (2.54 ± 0.77) × 1011 Jones. The champion PDs based on FAPbI3 MWs film and MAPbI3 MWs film show detectivity of 1.26 × 1013 and 9.67 × 1011 Jones, which are much higher than that of corresponding polycrystalline films and located on the top ranking of similar devices. [ABSTRACT FROM AUTHOR]

The success of using 2D Ruddlesden‐Popper metal halide perovskites (MHPs) in optoelectronic devices has ignited great interest as means for energy level tuning at the interface with 3D MHPs. Inter alia, the application of 2D phenylethylammonium lead quaternary iodide (PEA2PbI4)/3D MHPs interfaces has improved various optoelectronic devices, where a staggered type‐II energy level alignment is often assumed. However, a type‐II heterojunction seems to contradict the enhanced photoluminescence observed for 2D PEA2PbI4/3D MHP interfaces, which raises fundamental questions about the electronic properties of such junctions. In this study, using direct and inverse photoelectron spectroscopy, it is revealed that a straddling type‐I energy level alignment is present at 2D PEA2PbI4/3D methylammonium lead triiodide (MAPbI3) interfaces, thus explaining that the photoluminescence enhancement of the 3D perovskite is induced by energy transfer from the 2D perovskite. These results provide a reliable fundamental understanding of the electronic properties at the investigated 2D/3D MHP interfaces and suggest careful (re)consideration of the electronic properties of other 2D/3D MHP heterostructures. [ABSTRACT FROM AUTHOR]

In recent years the development of autonomous photo‐rechargeable batteries has received growing attention. Especially highly integrated photobatteries based on multifunctional materials able to harvest sunlight and store charge carriers are the holy grail amongst such devices. Recently 2‐(1‐cyclohexenyl)ethyl ammonium lead iodide (CHPI) has been reported as multifunctional photoelectrode material for the design of highly integrated Li‐ion photobatteries. CHPI is thereby believed to be able to reversibly intercalate Li‐ions from polar carbonate‐based electrolytes, typically used in Li‐ion batteries (LIBs). Herein, CHPI is examined closer to investigate its stability against dissolution, the possibility of Li‐intercalation and photo‐assisted deintercalation, and its general behavior under illumination in standard carbonate‐based electrolytes as well as in a newly developed low polarity electrolyte based on ortho‐difluorobenzene (o‐DFB). This study demonstrates that CHPI dissolves in contact with carbonate‐based electrolytes while being stable in o‐DFB‐based electrolyte and that no Li‐intercalation takes place in the latter. Furthermore, CHPI irreversibly photo‐corrodes during illumination and photo‐assisted deintercalation of lithium ions is not detected. These results lead to the conclusion, that CHPI is neither a suitable nor a stable material for the design of Li‐ion‐based photo‐rechargeable batteries and similar behavior for other organic–inorganic lead halide perovskite materials is expected. [ABSTRACT FROM AUTHOR]

Yellow‐phase formamidinium lead iodide (δ‐FAPbI3) as a degradation product of black perovskite phase is usually unwelcome in perovskite solar cells (PSCs). However, it also shows high potential in passivating defects and protecting perovskite films from moisture intrusion due to its water‐stable nature. Herein, the utilization of δ‐FAPbI3 to construct a yellow/black heterophase bilayer is reported, in which the perovskite layer is shielded by in situ formed δ‐FAPbI3 species on the surface, for PSCs with enhanced efficiency and stability. It is found that the δ‐FAPbI3 layer with a broader bandgap than the black‐phase perovskite can efficiently suppress the charge recombination at the interface, offering a high PSC efficiency of 23.10%. More importantly, the δ‐FAPbI3‐modified devices exhibit preferable stability against various external stresses to that of the control ones. Compared to those using the disliked δ‐FAPbI3 in the literature, the strategy, which maximizes its merits in reducing the interfacial charge recombination and stabilizing the perovskite structure, is more simple yet effective to realize highly efficient and stable PSCs. [ABSTRACT FROM AUTHOR]

Metal‐halide perovskites (MHPs) have made incredible achievements in the past few years, especially in the area of perovskite light‐emitting diodes (PeLEDs). Nevertheless, hole transport layers (HTLs) used in most highly efficient PeLEDs usually have low hole mobilities in the range of 10−4–10−6 cm2 V−1 s−1, much lower than that of MHPs, resulting in severe roll‐off and low radiance of the devices. Here, methylammonium lead iodide (MAPbI3) is successfully deposited on top of methylammonium lead chloride (MAPbCl3) using orthogonal solvent to form heterojunction PeLEDs (HJ‐PeLEDs). Due to the high hole mobility of MAPbCl3 ≈42 cm2 V−1 s−1, the HJ‐PeLEDs exhibit a peak external quantum efficiency of 10.7% and a high radiance of 157 W sr−1 m−2 at a low applied voltage of 3.9 V. Furthermore, the large‐area (28 cm2) HJ‐PeLEDs made by blade coating shows a uniform and high radiance of ≈180 W sr−1 m−2. This work provides a novel strategy to fabricate bright and large‐area PeLEDs to meet the requirements of commercial applications. [ABSTRACT FROM AUTHOR]

The conductivity of 2D perovskite is mainly dominated by halide metal octahedron skeletons. However, in contrast to 3D perovskite structures, the layered inorganic skeletons are easily compressed or stretched by large organic cations, causing serious microstrain with impaired optoelectronic responses. Here, fluorination modulated supramolecular interactions in 2D fluorophenethylammonium lead iodide (FPEA2PbI4) perovskites are reported. In the double layered organic spacer, interlayer supramolecular interactions between electronegative F atoms and electron‐rich benzene rings dominate the lattice microstrain of 2D (p‐FPEA)2PbI4 perovskite, which can be released by interlayer interactions pulling during compressively bending the flexible devices. This strong electrostatic interaction can maximally release the compression to the inorganic octahedron skeleton during compressive bending, leading to a maximum degree of released microstrain with improved stability. The 60% microstrain can be released by compressive bending, and the corresponding photocurrent response is recovered by about three times in (p‐FPEA)2PbI4 perovskite film. In contrast, intralayer supramolecular interactions dominate microstrain of 2D (o‐FPEA)2PbI4 perovskites, which prevents the microstrain release during compressive bending. The strong electrostatic interaction design in the organic spacer of 2D perovskite takes an important role in releasing the microstrain and re‐bursting the device performance of flexible perovskite devices. [ABSTRACT FROM AUTHOR]

Formamidinium lead iodide (FAPbI3) has endowed power conversion efficiencies (PCEs) up to 25.5% in regular‐structured perovskite solar cells (PSCs) because of its optimal bandgap and enhanced thermal stability. However, the performance of FAPbI3‐based inverted‐structured PSCs is unsatisfactory. Herein, four kinds of commonly used hole transport materials (HTMs) are selected, including PEDOT:PSS, PTAA, NiOx, and MeO‐2PACz, to study their impact on the methylamine chloride (MACl)‐assisted one‐step deposition of FAPbI3 films. It is found that MeO‐2PACz is the optimal substrate for stabilizing black‐phase FAPbI3 and the corresponding inverted‐structured PSCs show the best photovoltaic performance. Nonetheless, the PCE is restricted by low open‐circuit voltage (VOC) due to non‐radiative recombination caused by MACl residues. Therefore, homologous PbI2 in situ passivation is implemented to passivate defects at grain boundaries. The addition of excess PbI2 in precursor solution remarkably decreases charge trap densities and elongates carrier lifetimes. As a result, the optimized device achieves an impressive PCE of 22.13%, which is the highest efficiency of FAPbI3 based on inverted‐structured PSCs. Moreover, the best device exhibits free hysteresis and excellent long‐term stability, maintaining 92% of the initial PCEs after 800 h aging under ambient conditions. [ABSTRACT FROM AUTHOR]

The ionic nature endows halide perovskites with intrinsic interfacial defects in the formed polycrystalline films, thus imposing the challenge of synchronously passivating these defects with low formation energies that directly account for the unsatisfied performance of perovskite solar cells (PSCs). By virtue of the theoretically proven capability of a three to four times enhancement of the formation energy of each defect of Pb‐I antisite (PbI) and iodine vacancy (VI), a new passivation molecule of 1,10‐phenanthrolin‐5‐amine (PAA) is intentionally explored to synchronously passivate the dual defects. The pronounced passivation effect is experimentally verified by the sharp enhancement of the open‐circuit voltage in ternary PSCs from the original 1.118 up to 1.207 V, as well as the construction of PAA‐modified formamidinium lead iodide PSCs with a champion efficiency up to 24.06%, thus providing a universal alternative of addressing interfacial charge carrier dynamics and operational stability of PSCs that are bothered by the multiple interfacial defects. [ABSTRACT FROM AUTHOR]

All‐inorganic cesium lead iodide (CsPbI3) perovskites, which replace volatile and hygroscopic organic components with stable inorganic cesium cations, have promising photoelectronic properties for potential application in solar cells. However, highly stable and efficient CsPbI3‐based perovskite solar cells are rarely reported because the optically active black phases of CsPbI3 tend to change into a photo‐inactive yellow δ‐phase. Herein, a highly stable CsPbI3 film that is formed by introducing a small quantity of zwitterions with different dimensions to the perovskite precursor solution is reported. The zwitterions effectively inhibit the formation of the yellow δ‐phase during perovskite crystallization and promote the development of a stable black α‐phase. In addition, a systematic analysis reveals strong interaction between 3D zwitterions and perovskites in both the solution and film states, which leads to a dense and pinhole‐free CsPbI3 film with suppressed trap states. The resulting perovskite solar cells with 3D zwitterions achieve a significantly improved power conversion efficiency of 18.4% with high reproducibility. The devices without encapsulation retain 98% of the initial efficiency after 25 days at 25 °C and relative humidity of 25% ± 5%. Importantly, the 3D zwitterion‐based devices demonstrate excellent phase stability when subjected to thermal aging at 100 °C. [ABSTRACT FROM AUTHOR]

Wide‐bandgap perovskites have attracted substantial attention due to their important role in serving as a top absorber in tandem solar cells (TSCs). However, wide‐bandgap perovskite solar cells (PVSCs) typically suffer from severe non‐radiative recombination loss and therefore exhibit high open‐circuit voltage (VOC) deficits. To address these issues, a 2D octyl‐diammonium lead iodide interlayer is adopted onto the hole‐transporting layer to induce the formation of an ultrathin quasi‐2D perovskite that is close to the hole‐selective interface. This approach not only accelerates hole transfer and retards hole accumulation but also reduces the trap density in the perovskite layer on top, thereby efficiently suppresses non‐radiative recombination pathways. Consequently, the champion wide‐bandgap device (≈1.66 eV) exhibits a power conversion efficiency (PCE) of 21.05% with a VOC of 1.23 V, where the VOC deficit of 0.43 V is among the lowest values for inverted wide‐bandgap PVSCs. Moreover, by stacking a semi‐transparent perovskite top cell on a 1.1 eV Cu2ZnSn(S,Se)4 (CZTSSe) bottom cell, a 22.27% PCE was achieved on a perovskite/CZTSSe four‐terminal tandem solar cell, paving the way for all‐solution‐processed, low‐cost, and efficient TSCs with mitigated energy loss in the wide‐bandgap top cells. [ABSTRACT FROM AUTHOR]

Lattice dynamics are often regarded as signatures of the underlying crystal structure. Here, a first‐principle‐based effective Hamiltonian method combined with molecular dynamics simulations is used to study dynamical behaviors of CsPbI3 perovskite across temperature and structural phase transitions. A single (short‐range tilting) parameter in this effective Hamiltonian is varied in order to make the temperature range of the intermediate tetragonal P4/mbm phase, existing in‐between the cubic Pm3¯m and orthorhombic Pnma phases, either broader than observed or completely disappearing. Comparing the dynamics of these different cases allows one to conclude that real CsPbI3 perovskite should have i) two iodine‐octahedral‐tilt related modes that differ in frequency but both significantly soften as the temperature decreases within the cubic phase toward the Pm3¯m‐to‐P4/mbm transition; and ii) one mode that maintains a very low frequency (of the order of 1.0 cm−1) in the entire region of P4/mbm stability, as a result of the temporal exploration of various structural states. Such latter sub‐THz mode mixes fluctuations of antiphase iodine tiltings and Cs antipolar motions because of a trilinear energetic coupling. [ABSTRACT FROM AUTHOR]

The direct‐synthesis of conductive PbS quantum dot (QD) ink is facile, scalable, and low‐cost, boosting the future commercialization of optoelectronics based on colloidal QDs. However, manipulating the QD matrix structures still is a challenge, which limits the corresponding QD solar cell performance. Here, for the first time a coordination‐engineering strategy to finely adjust the matrix thickness around the QDs is presented, in which halogen salts are introduced into the reaction to convert the excessive insulating lead iodide into soluble iodoplumbate species. As a result, the obtained QD film exhibits shrunk insulating shells, leading to higher charge carrier transport and superior surface passivation compared to the control devices. A significantly improved power‐conversion efficiency from 10.52% to 12.12% can be achieved after the matrix engineering. Therefore, the work shows high significance in promoting the practical application of directly synthesized PbS QD inks in large‐area low‐cost optoelectronic devices. [ABSTRACT FROM AUTHOR]

There is an ongoing surge of interest in the use of formamidinium (FA) lead iodide perovskites in photovoltaics due to their exceptional optoelectronic properties. However, thermodynamic instability of the desired cubic perovskite (α‐FAPbI3) phase at ambient conditions leads to the formation of a yellow non‐perovskite (δ‐FAPbI3) phase that compromises its utility. A stable α‐FAPbI3 perovskite phase is achieved by employing benzylammonium iodide (BzI) and the microscopic structure is elucidated by using solid‐state NMR spectroscopy and X‐ray scattering measurements. Perovskite solar cells based on the FAPbI3(BzI)0.25 composition achieve power conversion efficiencies exceeding 20%, which is accompanied by enhanced shelf‐life and operational stability, maintaining 80% of the performance after one year at ambient conditions. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid perovskites have reached an unprecedented high efficiency in photovoltaic applications, which makes the commercialization of perovskite solar cells (PSCs) possible. In the past several years, particular attention has been paid to the stability of PSC devices, which is a critical issue for becoming a practical photovoltaic technology. In particular, the interface‐induced degradation of perovskites should be the dominant factor causing poor stability. Here, imidazole bromide functionalized graphene quantum dots (I‐GQDs) are demonstrated to regulate the interface between the electron transport layer (ETL) and formamidinium lead iodide (FAPbI3) perovskite layer. The incorporation of I‐GQDs not only reduces the interface defects for achieving a better energy level alignment between ETL and perovskite, but also improves the film quality of FAPbI3 perovskite including enlarged grain size, lower trap density, and a longer carrier lifetime. Consequently, the planar FAPbI3 PSCs with I‐GQDs regulation achieve a high efficiency of 22.37% with enhanced long‐term stability. [ABSTRACT FROM AUTHOR]

While the challenges associated with the stability of metal halide perovskites are well known and intensely studied, variability in electronic properties represents an equally significant, yet seldom studied, challenge that could potentially slow or inhibit the commercial viability of these systems. In this work, the contactless characterization technique time‐resolved microwave conductivity (TRMC) is used to quantify the variability in electronic properties of the prototypical perovskite, methylammonium lead iodide (MAPbI3) both between different samples, and at different locations within the same sample. Using scanning electron microscopy (SEM) and a quasi‐automated image‐analysis strategy, it is possible to evaluate the metrics of heterogeneity in surface microstructure and correlate them with the electronic properties as obtained by TRMC. Substantial intra‐sample and inter‐sample variation is observed in the mobility‐yield product in samples prepared following differing protocols, and in samples prepared following identical protocols. [ABSTRACT FROM AUTHOR]

All‐inorganic perovskite cesium lead iodide (CsPbI3) exhibits excellent prospects for commercial application as a light absorber in single‐junction or tandem solar cells due to its outstanding thermal stability and proper bandgap. However, the device performance of CsPbI3‐based perovskite solar cells (PSCs) is still restricted by the unsatisfactory crystal quality and severe non‐radiative recombination. Herein, inorganic additive ammonium halides are introduced into the precursor solution to regulate the nucleation and crystallization of the CsPbI3 film by exploiting the atomic interaction between the ammonium group and the Pb–I framework. The grain boundaries and interfacial contact of the CsPbI3 film have been improved, which leads to significant suppression in the non‐radiative recombination and an enhancement in the charge transport ability. With these benefits, a high efficiency of 18.7% together with an extraordinarily high fill factor of 0.83–0.84 has been achieved, comparable to the highest records reported so far. Moreover, the cell exhibits ultra‐high photoelectrical stability under continuous light illumination and high bias voltage with 96% of its initial power‐conversion efficiency being sustained after 2000 h operation, even superior to the world‐champion CsPbI3 solar cell. The findings are promising for the development and application of all‐inorganic PSCs using a simple inorganic additive strategy. [ABSTRACT FROM AUTHOR]

Methylammonium lead iodide (MAPbI3) perovskite has garnered significant interest as a versatile material for optoelectronic applications. The temperature‐dependent photoluminescence (TDPL) and phase‐transition behaviors revealed in previous studies have become standard indicators of defects, stability, charge carrier dynamics, and device performance. However, published reports abound with examples of irregular photoluminescence and phase‐transition phenomena that are difficult to reconcile, posing major challenges in the correlation of those properties with the actual material state or with the subsequent device performance. In this paper, a unifying explanation for the seemingly inconsistent TDPL and phase‐transition (orthorhombic‐to‐tetragonal) characteristics observed for MAPbI3 is presented. By investigating MAPbI3 perovskites with varying crystalline states, ranging from polycrystal to highly oriented crystal as well as single‐crystals, key features in the TDPL and phase‐transition behaviors are identified that are related to the extent of crystal domain‐size‐dependent residual stress and stem from the considerable volume difference (ΔV ≈ 4.5%) between the primitive unit cells of the orthorhombic (at 80 K) and tetragonal phases (at 300 K) of MAPbI3. This fundamental connection is essential for understanding the photophysics and material processing of soft perovskites. [ABSTRACT FROM AUTHOR]

The soft nature of organic–inorganic halide perovskites renders their lattice particularly tunable to external stimuli such as pressure, undoubtedly offering an effective way to modify their structure for extraordinary optoelectronic properties. Here, using the methylammonium lead iodide as a representative exploratory platform, it is observed that the pressure‐driven lattice disorder can be significantly suppressed via hydrogen isotope effect, which is crucial for better optical and mechanical properties previously unattainable. By a comprehensive in situ neutron/synchrotron‐based analysis and optical characterizations, a remarkable photoluminescence (PL) enhancement by threefold is convinced in deuterated CD3ND3PbI3, which also shows much greater structural robustness with retainable PL after high peak‐pressure compression–decompression cycle. With the first‐principles calculations, an atomic level understanding of the strong correlation among the organic sublattice and lead iodide octahedral framework and structural photonics is proposed, where the less dynamic CD3ND3+ cations are vital to maintain the long‐range crystalline order through steric and Coulombic interactions. These results also show that CD3ND3PbI3‐based solar cell has comparable photovoltaic performance as CH3NH3PbI3‐based device but exhibits considerably slower degradation behavior, thus representing a paradigm by suggesting isotope‐functionalized perovskite materials for better materials‐by‐design and more stable photovoltaic application. [ABSTRACT FROM AUTHOR]

Even though halide perovskite materials have been increasingly investigated as flexible devices, mechanical properties under flexible environments have rarely been reported on. Herein, a nonconventional deposition technique that can generate extra compressive or tensile stress in representative inorganic CsPbBr3 and hybrid MAPbI3 (methylammonium lead iodide) halide perovskites is proposed for higher mechanical flexibility. As an impressive result of bending fracture evaluation, fracture energy is substantially improved by ≈260% for CsPbBr3 and ≈161% for MAPbI3 with the maximum compressive strain of −1.33%. Origin of the flexibility enhancements by the in situ strain is verified with structural simulation where the anisotropic lattice distortion, that is, contraction in the ab plane and elongation along the c‐axis, is evident with changes in atomic bond lengths and angles in the halide perovskites. Other mechanical properties such as hardness, film strength, and fracture toughness are also discussed with direct comparisons between the inorganic and hybrid halides. Beyond the successful adjustment of this in situ deposition technique, the strain‐dependent mechanical properties are expected to be extensively useful for designing halides‐based flexible devices. [ABSTRACT FROM AUTHOR]

Halide perovskite like methylammonium lead iodide perovskite (MAPbI3) with its prominent optoelectronic properties has triggered substantial concerns in photocatalytic H2 evolution. In this work, to attain preferable photocatalytic performance, a MAPbI3/cobalt phosphide (CoP) hybrid heterojunction is constructed by a facile in situ photosynthesis approach. Systematic investigations reveal that the CoP nanoparticle can work as co‐catalyst to not only extract photogenerated electrons effectively from MAPbI3 to improve the photoinduced charge separation, but also facilitate the interfacial catalytic reaction. As a result, the as‐achieved MAPbI3/CoP hybrid displays a superior H2 evolution rate of 785.9 µmol h−1 g−1 in hydroiodic acid solution within 3 h, which is ≈8.0 times higher than that of pristine MAPbI3. Furthermore, the H2 evolution rate of MAPbI3/CoP hybrid can reach 2087.5 µmol h−1 g−1 when the photocatalytic reaction time reaches 27 h. This study employs a facile in situ photosynthesis strategy to deposit the metal phosphide co‐catalyst on halide perovskite nanocrystals to conduct photocatalytic H2 evolution reaction, which may stimulate the intensive investigation of perovskite/co‐catalyst hybrid systems for future photocatalytic applications. [ABSTRACT FROM AUTHOR]

Methylammonium lead iodide (MAPI) is the archetype of the intensively researched class of perovskites for photovoltaics. Nonetheless, even equilibrium aspects are far from being fully understood. Equilibrium space charge effects at the MAPI/TiO2 and MAPI/Al2O3 interfaces are discussed, which are of paramount significance for solar cells. Different from the photovoltaic literature in which such built‐in potentials are considered as being generated solely by electronic charge carriers, a generalized picture that considers the equilibrium distribution of both ionic and electronic carriers is applied. Experimental evidence is given that shows it is the ions that are responsible for the equilibrium space charge potential, the reason being a pronounced ion adsorption at the contacts. The electronic redistribution is a sheer consequence of the so‐established electric field. Experiments with mesoporous oxide as well as experiments with MAPbBr3 (MAPBr) indicate photovoltaic relevance and material generality in terms of the choice of the lead‐based perovskite. The occurrence of space charge effects at heterojunctions generated by ionic redistribution is not only a novel concept in photovoltaics, it also provides a new path to modifying charge‐selective interfaces, as well as a better understanding of the behavior in mesoporous systems. [ABSTRACT FROM AUTHOR]

Organic–inorganic halide perovskites are intrinsically unstable when exposed to moisture and/or light. Additionally, the presence of lead in many perovskites raises toxicity concerns. Herein, a thin film of barium zirconium sulfide (BaZrS3), a lead‐free chalcogenide perovskite, is reported. Photoluminescence and X‐ray diffraction measurements show that BaZrS3 is far more stable than methylammonium lead iodide (MAPbI3) in moist environments. Moisture‐ and light‐induced degradations in BaZrS3 and MAPbI3 are compared by using simulations and calculations based on density functional theory. The simulations reveal drastically slower degradation in BaZrS3 due to two factors—weak interaction with water and very low rates of ion migration. BaZrS3 photodetecting devices with photoresponsivity of ≈46.5 mA W−1 are also reported. The devices retain ≈60% of their initial photoresponse after 4 weeks under ambient conditions. Similar MAPbI3 devices degrade rapidly and show a ≈95% decrease in photoresponsivity in just 4 days. The findings establish the superior stability of BaZrS3 and strengthen the case for its use in optoelectronics. New possibilities for thermoelectric energy conversion using these materials are also demonstrated. [ABSTRACT FROM AUTHOR]

Hybrid organic–inorganic perovskites such as methylammonium lead iodide have emerged as promising semiconductors for energy‐relevant applications. The interactions between charge carriers and lattice vibrations, giving rise to polarons, have been invoked to explain some of their extraordinary optoelectronic properties. Here, time‐resolved optical spectroscopy is performed, with off‐resonant pumping and electronic probing, to examine several representative lead iodide perovskites. The temporal oscillations of electronic bandgaps induced by coherent lattice vibrations are reported, which is attributed to antiphase octahedral rotations that dominate in the examined 3D and 2D hybrid perovskites. The off‐resonant pumping scheme permits a simplified observation of changes in the bandgap owing to the Ag vibrational mode, which is qualitatively different from vibrational modes of other symmetries and without increased complexity of photogenerated electronic charges. The work demonstrates a strong correlation between the lead–iodide octahedral framework and electronic transitions, and provides further insights into the manipulation of coherent optical phonons and related properties in hybrid perovskites on ultrafast timescales. [ABSTRACT FROM AUTHOR]

A first‐principles‐based effective Hamiltonian is developed and employed to investigate finite‐temperature structural properties of a prototype of perovskite halides, that is CsPbI3. Such simulations, when using first‐principles‐extracted coefficients, successfully reproduce the existence of an orthorhombic Pnma state and its iodine octahedral tilting angles around room temperature. However, they also yield a direct transformation from Pnma to cubic Pm3¯m upon heating, unlike measurements that reported the occurrence of an intermediate long‐range‐tilted tetragonal P4/mbm phase in‐between the orthorhombic and cubic phases. Such disagreement, which may cast some doubts about the extent to which first‐principle methods can be trusted to mimic hybrid perovskites, can be resolved by "only" changing one short‐range tilting parameter in the whole set of effective Hamiltonian coefficients. In such a case, some reasonable values of this specific parameter result in the predictions that i) the intermediate P4/mbm state originates from fluctuations over many different tilted states; and ii) the cubic Pm3¯m phase is highly locally distorted and develops strong transverse antiphase correlation between first‐nearest neighbor iodine octahedral tiltings, before undergoing a phase transition to P4/mbm under cooling. [ABSTRACT FROM AUTHOR]

Perovskite solar cells have attracted a great deal of attention thanks to their high efficiency, ease of manufacturing, and potential low cost. However, the stability of these devices is considered their main drawback and needs to be addressed. Mesoporous carbon perovskite solar cells (m‐CPSC), consisting of three mesoporous layers (TiO2/ZrO2/C) infiltrated with CH3NH3PbI3 (MAPI) perovskite, have presented excellent lifetimes of more than 10 000 h when the additive NH2(CH2)4CO2HI (5‐ aminovaleric acid iodide; 5‐AVAI) is used to modify the perovskite structure. Yet, the role of 5‐AVAI in enhancing the stability has yet to be determined. Here, superoxide‐mediated degradation of MAPI m‐CPSC with and without the 5‐AVAI additive is studied using the fluorescence probe dihydroethidium for superoxide detection. In situ X‐ray diffractometry shows that aminovaleric acid methylammonium lead iodide (AVA‐MAPI) perovskite infiltrated in mesoporous layers presents higher stability in an ambient environment under illumination, evidenced by a slower decrease of the MAPI/PbI2 peak ratio. Superoxide yield measurements demonstrate that AVA‐MAPI generates more superoxide than regular MAPI when deposited on glass but generates significantly less when infiltrated in mesoporous layers. It is believed that superoxide formation in m‐CPSC is dependent on a combination of competitive factors including oxygen diffusion, sample morphology, grain size, and defect concentration. [ABSTRACT FROM AUTHOR]

The engineering of the electron transport layer (ETL)/light absorber interface is explored in perovskite solar cells. Single‐crystalline TiO2 nanorod (NR) arrays are used as ETL and methylammonium lead iodide (MAPI) as light absorber. A dual ETL surface modification is investigated, namely by a TiCl4 treatment combined with a subsequent PC61BM monolayer deposition, and the effects on the device photovoltaic performance were evaluated with respect to single modifications. Under optimized conditions, for the combined treatment synergistic effects are observed that lead to remarkable enhancements in cell efficiency, from 14.2% to 19.5%, and to suppression of hysteresis. The devices show JSC, VOC, and fill factor as high as 23.2 mA cm−2, 1.1 V, and 77%, respectively. These results are ascribed to a more efficient charge transfer across the ETL/perovskite interface, which originates from the passivation of defects and trap states at the ETL surface. To the best of our knowledge, this is the highest cell performance ever reported for TiO2 NR‐based solar cells fabricated with conventional MAPI light absorber. Perspective wise, this ETL surface functionalization approach combined with more recently developed and better performing light absorbers, such as mixed cation/anion hybrid perovskite materials, is expected to provide further performance enhancements. [ABSTRACT FROM AUTHOR]

Studies on the photoelectronic properties of perovskite solar cells (PSCs) made from non‐PbI2 precursors are seldom reported. In this study, a series of transient techniques are applied to investigate the charge recombination and trap distribution in an efficient PSC fabricated using a low‐toxicity Pb(NO3)2/water protocol. A device with identical conversion efficiency fabricated using a conventional PbI2/dimethylformamide protocol is also studied for comparison. Transient photovoltage and time‐resolved photoluminescence analysis reveal that the Pb(NO3)2/water‐based device exhibits a long lifetime in both bimolecular and trap‐assisted recombination. However, differential capacitance and differential charging analysis indicate that there are more charges stored in the Pb(NO3)2/water‐based perovskite layer, which stretches the energy tail from band edge to midband and should provoke serious trap‐assisted recombination. The exceptional long electron lifetime in the Pb(NO3)2/water‐based device is explained by a benign defect inactivation, which originates from water and NO3− residues from the aqueous precursor solution and is involved in the formation of perovskite crystal. Consequently, despite the perovskite film made from Pb(NO3)2/water protocol possessing high trap density, its photovoltaic device still exhibits a long electron lifetime and superior photovoltaic properties. [ABSTRACT FROM AUTHOR]

The exploration of the synthetic space of halide perovskites hinges on an enormous number of parameters requiring time‐consuming experimentation to decouple and optimize. Here, the formation of the prototype material CH3NH3PbI3 (MAPbI3) is investigated at different time and length scales using multimodal in situ measurements to monitor the evolution of crystalline phases, morphology, and photoluminescence as a function of the lead precursors. Kinetically fast formation of crystalline precursor phases already during the spin‐coat deposition is observed using lead iodide (PbI2) or lead chloride (PbCl2) routes. These precursor phases most likely template final MAPbI3 film morphology. In particular, the emergence of the "needle‐like" structure is shown to appear before film annealing. In situ photoluminescence measurements suggest nanoscale nucleation followed by rapid nuclei densification and growth. Using this multimodal in situ approach, different formation pathways can be identified either via precursor phases in the PbI2 and PbCl2 routes or direct perovskite formation from molecular building blocks as observed in the lead acetate (PbAc2) route. Correlation of in situ results with photovoltaic device performance demonstrates the power of in situ multimodal techniques, paves the way to a fast screening of synthetic parameters, and ultimately leads to controlled synthetic procedures that yield high‐efficiency devices. [ABSTRACT FROM AUTHOR]

Abstract: Solar cells with light‐absorbing layers comprising organometal halide perovskites have recently exceeded 22% efficiency. Despite high power‐conversion efficiencies, the stability of these devices, particularly when exposed to humidity and oxygen, remains poor. In the current study, a pathway to increase the stability of methylammonium lead iodide (CH3NH3PbI3) based solar cells towards humidity is demonstrated, while maintaining the simplicity and solution‐processability of the active layers. Thermal annealing of the precursor solution prior to deposition induces the formation of cubic‐phase perovskite films in the solid state at room temperature. The experiments demonstrate that this improved ambient stability is correlated with the presence of the cubic phase at device operating temperatures, with the cubic phase resisting the formation of perovskite monohydrate—a pathway of degradation in conventionally processed perovskite thin films—on exposure to humidity. [ABSTRACT FROM AUTHOR]

Organic-inorganic hybrid perovskite solar cells have emerged as one of the promising photovoltaic candidates to generate renewable energy. However, the large amounts of grain boundaries and trap states that exist in the bulk or interfacial regions of perovskite films limit further enhancement of device efficiency. Herein, an additive engineering strategy is introduced employing trimethylammonium chloride in the methylammonium iodide precursor solution to prepare methylammonium lead iodide perovskite films with reduced grain boundaries and trap densities. This leads to an increased charge carrier diffusion coefficient and diffusion length, as evaluated by impedance and voltage decay measurements, intensity-modulated photovoltage, and photocurrent spectroscopies. The proportion of nonradiative recombination processes is significantly reduced, consequently increasing device efficiency from 19.1% to 20.9% in these perovskite solar cells. [ABSTRACT FROM AUTHOR]

Abstract: The sensitivity of organic–inorganic perovskites to environmental factors remains a major barrier for these materials to become commercially viable for photovoltaic applications. In this work, the degradation of formamidinium lead iodide (FAPbI3) perovskite in a moist environment is systematically investigated. It is shown that the level of relative humidity (RH) is important for the onset of degradation processes. Below 30% RH, the black phase of the FAPbI3 perovskite shows excellent phase stability over 90 d. Once the RH reaches 50%, degradation of the FAPbI3 perovskite occurs rapidly. Results from a Kelvin probe force microscopy study reveal that the formation of nonperovskite phases initiates at the grain boundaries and the phase transition proceeds toward the grain interiors. Also, ion migration along the grain boundaries is greatly enhanced upon degradation. A post‐thermal treatment (PTT) that removes chemical residues at the grain boundaries which effectively slows the degradation process is developed. Finally, it is demonstrated that the PTT process improves the performance and stability of the final device. [ABSTRACT FROM AUTHOR]

Crystal engineering of CH3NH3PbI3 perovskite materials through templatedirected nucleation and growth on PbI2 nuclei dispersed in a polar fullerene (C60 pyrrolidine tris-acid, CPTA) electron transport layer (ETL) (CPTA:PbI2) is proposed as a route for controlling crystallization kinetics and grain sizes. Chemical analysis of the CPTA:PbI2 template confirms that CPTA carboxylic acid groups can form a monodentate or bidentate chelate with Pb(II), resulting in a lower nucleation barrier that promotes rapid formation of the tetragonal perovskite phase. Moreover, it is demonstrated that a uniform CH3NH3PbI3 film with highly crystalline and large domain sizes can be realized by increasing the spacing between nuclei to retard perovskite crystal growth via careful control of the preferred nucleation site distribution in the CPTA:PbI2 layer. The improved perovskite morphology possesses a long photoluminescence lifetime and efficient photocarrier transport/separation properties to eliminate the hysteresis effect. The corresponding planar heterojunction photovoltaic yields a high power conversion efficiency (PCE) of 20.20%, with a high fill factor (FF) of 81.13%. The average PCE and FF values for 30 devices are 19.03% ± 0.57% and 78.67% ± 2.13%, respectively. The results indicate that this ETL template-assisted crystallization strategy can be applied to other organometal halide perovskite-based systems. [ABSTRACT FROM AUTHOR]

Traps limit the photovoltaic efficiency and affect the charge transport of optoelectronic devices based on hybrid lead halide perovskites. Understanding the nature and energy scale of these trap states is therefore crucial for the development and optimization of solar cell and laser technology based on these materials. Here, the low-temperature photoluminescence of formamidinium lead triiodide (HC(NH2)2PbI3) is investigated. A power-law time dependence in the emission intensity and an additional low-energy emission peak that exhibits an anomalous relative Stokes shift are observed. Using a rate-equation model and a Monte Carlo simulation, it is revealed that both phenomena arise from an exponential trap-density tail with characteristic energy scale of ≈3 meV. Charge-carrier recombination from sites deep within the tail is found to cause emission with energy downshifted by up to several tens of meV. Hence, such phenomena may in part be responsible for open-circuit voltage losses commonly observed in these materials. In this high-quality hybrid perovskite, trap states thus predominantly comprise a continuum of energetic levels (associated with disorder) rather than discrete trap energy levels (associated, e.g., with elemental vacancies). Hybrid perovskites may therefore be viewed as classic semiconductors whose band-structure picture is moderated by a modest degree of energetic disorder. [ABSTRACT FROM AUTHOR]

Formamidinium lead iodide (FAPbI3) has a broader absorption spectrum and better thermal stability than the most famous methylammonium lead iodide, thus exhibiting great potential for photovoltaic applications. In this report, the light-induced photoluminescence (PL) evolution in FAPbI3 thin films is investigated. The PL intensity evolution is found to be strongly dependent on the atmosphere surrounding the samples. When the film is exposed to air, its photoluminescence intensity is enhanced more than 140 times after continuous ultraviolet laser illumination for 2 h, and the average lifetime is prolonged from 17 to 389 ns. The enhanced photoluminescence implies that the trap density is significantly reduced. The comparative study of the photoluminescence properties in air, nitrogen, and oxygen/helium environment suggests that moisture is important for the PL enhancement. This is explained in terms of moisture-assisted light-healing effect in FAPbI3 thin films. With this study, a new method is demonstrated to increase and control the quality of hybrid perovskite thin films. [ABSTRACT FROM AUTHOR]

Despite the high power conversion efficiency and ease of fabrication, planar-junction organolead halide perovskite solar cells often exhibit anomalous hysteretic current-voltage ( I-V) characteristics. In this work, the origin of the I-V hysteresis is studied by fine-tuning the precursor ratio of methylammonium lead iodide and thus varying the native defects in the material. It is shown that the perovskites synthesized from 'PbI2 excess,' 'methylammonium iodide excess,' and 'stoichiometric' precursors exhibit identical film morphology but different I-V hysteresis in a planar solar cell configuration. Through a comparative analysis on the temperature-dependent continuous and stepwise-stabilized I-V responses of the three devices, a model involving transport and trapping of the ionic native defects is proposed. The active energy of the transport process is estimated to be between 0.10 and 0.18 eV, most likely associated with the vacancy-mediated iodide ion migration. The lower activation energy of the 'PbI2 excess' and 'Stoichiometric' samples indicates that the presence of methylammonium vacancies may provide a favorable pathway for the migration of iodide ions due to reduced steric hindrance. Furthermore, the slow trapping and release processes of iodide ions at the TiO2/perovskite interface are accounted for the long time scale current decay (or raise) following a voltage change. [ABSTRACT FROM AUTHOR]

Halide Perovskites: Suppressed Lattice Disorder for Large Emission Enhancement and Structural Robustness in Hybrid Lead Iodide Perovskite Discovered by High-Pressure Isotope Effect (Adv. Funct. Perovskite, high-pressure, bandgap, mechanical and optical properties, stability Keywords: perovskite; high-pressure; bandgap; mechanical and optical properties; stability EN perovskite high-pressure bandgap mechanical and optical properties stability 1 1 1 02/26/21 20210224 NES 210224 In article number 2009131, Gang Liu and co-workers conduct high-pressure isotope research to discover a significantly suppressed lattice disorder realized by H/D substitution in hybrid halide perovskites, which reveals large emission enhancement and strong structural robustness in isotope-functionalized perovskite materials. [Extracted from the article]

Seemingly contradictory reports on polar domains and their origin have surrounded the controversial discussion about the ferroelectricity of the methyl ammonium lead iodide (MAPbI3) thin films that are commonly employed in perovskite solar cells. In this work, microscopic modulations of the polar domain patterns upon application of an electric poling field are correlated with macroscopic changes to the currents through the MAPbI3 layer. Piezoresponse force microscopy is used to monitor the widening, narrowing, generation or extinction of polar domains, as well as shifts of the domain walls at room temperature under an in‐plane electric poling field that is applied between two laterally organized electrodes. This poling leads to a net polarization of individual grains and the thin film itself. Macroscopically, this net polarization results in a persistent shift of the diode characteristics that is measured across the channel between the electrodes. Both the modulation of the polar domains upon electric poling and the concurrent persistent shift of the electric currents through the device are the unambiguous hallmarks of ferroelectricity, which demonstrate that MAPbI3 is a ferroelectric semiconductor. [ABSTRACT FROM AUTHOR]