Enhancing the Optoelectronic Performance of Perovskite Solar Cells via a Textured CH3NH3PbI3 Morphology

Perovskite‐based solar cells are generally assembled as planar structures comprising a flat organoammonium metal halide perovskite layer, or mesoscopic structures employing a mesoporous metal‐oxide scaffold into which the perovskite material is infiltrated. To present, little attention has been directed toward the texturing of the perovskite material itself. Herein, a textured CH₃NH₃PbI₃ morphology formed through a thin mesoporous TiO₂ seeding layer and a gas‐assisted crystallization method is reported. The textured morphology comprises a multitiered nanostructure, which allows for significant improvements in the light harvesting and charge extraction performance of the solar cells. Due to these improvements, average short‐circuit current densities for a batch of 28 devices are in excess of 22 mA cm^?2, and the maximum recorded power conversion efficiency is 16.3%. The performance gains concomitant with this textured CH₃NH₃PbI₃ morphology provide further insights into how control of the perovskite microstructure can be used to enhance the cell performance.     

Efficient Perovskite Hybrid Photovoltaics via Alcohol‐Vapor Annealing Treatment

In this work, alcohol‐vapor solvent annealing treatment on CH₃NH₃PbI₃ thin films is reported, aiming to improve the crystal growth and increase the grain size of the CH₃NH₃PbI₃ crystal, thus boosting the performance of perovskite photovoltaics. By selectively controlling the CH₃NH₃I precursor, larger‐grain size, higher crystallinity, and pinhole‐free CH₃NH₃PbI₃ thin films are realized, which result in enhanced charge carrier diffusion length, decreased charge carrier recombination, and suppressed dark currents. As a result, over 43% enhanced efficiency along with high reproducibility and eliminated photocurrent hysteresis behavior are observed from perovskite hybrid solar cells (pero‐HSCs) where the CH₃NH₃PbI₃ thin films are treated by methanol vapor as compared with that of pristine pero‐HSCs where the CH₃NH₃PbI₃ thin films are without any alcohol vapor treatment. In addition, the dramatically restrained dark currents and raised photocurrents give rise to over ten times enhanced detectivities for perovskite hybrid photodetectors, reaching over 10¹³ cm Hz^1/2 W^?1 (Jones) from 375 to 800 nm. These results demonstrate that the method provides a simple and facile way to boost the device performance of perovskite photovoltaics.     

Self-Assembled Perovskite Nanoislands on CH3NH3PbI3 Cuboid Single Crystals by Energetic Surface Engineering

Organometal perovskite single crystals have been recognized as a promising platform for high-performance optoelectronic devices, featuring high crystallinity and stability. However, a high trap density and structural nonuniformity at the surface have been major barriers to the progress of single crystal-based optoelectronic devices. Here, the formation of a unique nanoisland structure is reported at the surface of the facet-controlled cuboid MAPbI₃ (MA = CH₃NH₃⁺) single crystals through a cation interdiffusion process enabled by energetically vaporized CsI. The interdiffusion of mobile ions between the bulk and the surface is triggered by thermally activated CsI vapor, which reconstructs the surface that is rich in MA and CsI with reduced dangling bonds. Simultaneously, an array of Cs-Pb-rich nanoislands is constructed on the surface of the MAPbI₃ single crystals. This newly reconstructed nanoisland surface enhances the light absorbance over 50% and increases the charge carrier mobility from 56 to 93 cm² V⁻¹ s⁻¹. As confirmed by Kelvin probe force microscopy, the nanoislands form a gradient band bending that prevents recombination of excess carriers, and thus, enhances lateral carrier transport properties. This unique engineering of the single crystal surface provides a pathway towards developing high-quality perovskite single-crystal surface for optoelectronic applications.     

Using Bulk Heterojunctions and Selective Electron Trapping to Enhance the Responsivity of Perovskite–Graphene Photodetectors

Graphene field effect transistor sensitized by a layer of semiconductor (sensitizer/GFET) is a device structure that is investigated extensively for ultrasensitive photodetection. Among others, organometallic perovskite semiconductor sensitizer has the advantages of long carrier lifetime and solution processable. A further step to improve the responsivity is to design a structure that can promote electron–hole separation and selective carrier trapping in the sensitizer. Here, the use of a hybrid perovskite–organic bulk heterojunction (BHJ) as the light sensitizer to achieve this goal is demonstrated. Our spectroscopy and device measurements show that the CH₃NH₃PbI₃–PCBM BHJ/GFET device has improved charge separation yield and carrier lifetime as compared to a reference device with a CH₃NH₃PbI₃ sensitizer only. The key to these enhancement is the presence of [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM), which acts as charge separation and electron trapping sites, resulting in a 30‐fold increase in the photoresponsivity. This work shows that the use of a small amount of electron or hole acceptors in the sensitizer layer can be an effective strategy for improving and tuning the photoresponsivity of sensitizer/GFET photodetectors.     

Single‐Crystal Hybrid Perovskite Platelets on Graphene: A Mixed‐Dimensional Van Der Waals Heterostructure with Strong Interface Coupling

Van der Waals (vdW) heterostructures open up excellent prospects in electronic and optoelectronic applications. In this work, mixed‐dimensional metal‐halide perovskite/graphene heterostructures are prepared through selective growth of CH₃NH₃PbBr₃ platelets on patterned single‐layer graphene using chemical vapor deposition. Preferred growth of single‐crystal CH₃NH₃PbBr₃ platelets on graphene surfaces is achieved, which is accompanied by significant photoluminescence quenching. Raman spectra reveal that perovskite platelets cause p‐type doping in the graphene layer. A significant Fermi level decrease of 272 meV in graphene is estimated, which corresponds to a high doping density of 7.5 × 10¹² cm^?2. Surface potentials measured by Kelvin probe force microscopy indicate a negatively charged perovskite surface under illumination, which is consistent with the upward band bending deduced from conducting atomic force microscopy measurements. Moreover, a field‐effect phototransistor is fabricated using the perovskite/graphene heterostructure channel, and the increased Dirac voltage under illumination confirms an enhanced p‐type character in graphene. These findings enrich the understanding of strong interface coupling in such mixed‐dimensional vdW heterostructures and pave the way toward novel perovskite‐based optoelectronic devices.     

Enhanced Device Performance of Perovskite Photovoltaics by Magnetic Field‐Aligned Perovskites‐Magnetic Nanoparticles Composite Thin Film

Perovskite photovoltaics have drawn great attention in both academic and industrial sectors in the past decade. To date, impressive device performance has been achieved in state‐of‐the‐art device architectures through morphological manipulation and generic interface engineering. In this study, enhanced device performance of perovskite photovoltaics by magnetic field‐aligned CH₃NH₃PbI₃‐mixed Fe₃O₄ magnetic nanoparticles (CH₃NH₃PbI₃:Fe₃O₄) composite thin films is reported. It is found that magnetic field‐aligned CH₃NH₃PbI₃:Fe₃O₄ composite thin films possess superior film morphology, boosted and balanced charge carrier mobility, and suppressed trap density. Moreover, perovskite photovoltaics by magnetic field‐aligned CH₃NH₃PbI₃:Fe₃O₄ composite thin films exhibit suppressed charge carrier recombination and shorter charge carrier extraction time. As a result, perovskite solar cells by magnetic field‐aligned CH₃NH₃PbI₃:Fe₃O₄ composite thin films exhibit 20.23% power conversion efficiency with significantly reduced photocurrent hysteresis. Moreover, perovskite photodetectors by magnetic field‐aligned CH₃NH₃PbI₃:Fe₃O₄ composite thin films exhibit a photoresponsivity of 858 mA W^?1, a photodetectivity over 10¹³ Jones (1 Jones = 1 cm Hz^1/2 W^?1) and a linear dynamic range over 160 dB at room temperature. All these device performance parameters are significantly better than those by pristine CH₃NH₃PbI₃ thin film. Thus, these studies provide a facile way to boost device performance of perovskite photovoltaics.     

Deciphering the NH4PbI3 Intermediate Phase for Simultaneous Improvement on Nucleation and Crystal Growth of Perovskite

The NH₄PbI₃‐based phase transformation is realized by simply adding NH₄I additive, in order to simultaneously control perovskite nucleation and crystal growth. Regarding the nucleation process, the NH₄⁺ with small ionic radius preferentially diffuses into the [PbI₆]^4? octahedral layer to form NH₄PbI₃, which compensates the lack of CH₃NH₃I (MAI) precipitation. The generation of NH₄PbI₃ intermediate phase results in extra heterogeneous nucleation sites and reduces the defects derived from the absence of MA⁺. Regarding the crystal growth process, the cation exchange process between MA⁺ and NH₄⁺, instead of the MAs directly entering, successfully retards the crystal growth. Such NH₄PbI₃ consumption process slows down the crystal growth, which effectively improves the perovskite quality with lowered defect density. The cooperation of these two effects eventually leads to the high‐quality perovskite with enlarged grain size, prolonged photoluminescence lifetime, lowered defect density, and increased carrier concentration, as well as the finally enhanced photovoltaic performance. Moreover, NH₃ as a byproduct further facilitates the proposed transformation process and no external residue remains even without any post‐treatment. Such methodology of introducing a novel phase transformation to simultaneously control nucleation and crystal growth processes is of universal significance for further devotion in the foreseeable perovskite solar cells (PSCs) evolution.     

High‐Quality Cuboid CH3NH3PbI3 Single Crystals for High Performance X‐Ray and Photon Detectors

Organic–inorganic halide hybrid perovskite materials are promising materials for X‐ray and photon detection due to their superior optoelectronic properties. Single‐crystal (SGC) perovskites have increasingly attracted attention due to their substantially low crystal defects, which contribute to improving the figures of merit of the devices. Cuboid CH₃NH₃PbI₃ SGC with the naturally favorable geometry for device fabrication is rarely reported in X‐ray and photon detection application. The concept of seed dissolution‐regrowth to improve crystal quality of cuboid CH₃NH₃PbI₃ SGC is proposed and a fundamental understanding of the nucleation and growth is provided thermodynamically. The X‐ray detector fabricated from cuboid CH₃NH₃PbI₃ SGC demonstrates the firstly reported high sensitivity of 968.9 µC^?1 Gy^?1 cm^?2 under ?1 V bias. The results also show that the favorable crystal orientation and high quality of cuboid CH₃NH₃PbI₃ leads to better responsivity and faster response speed than the more common dodecahedral CH₃NH₃PbI₃ in photodetection. Consequently, the work paves a way to synthesize high‐quality perovskite SGCs and benefits the application of MAPbI₃ SGCs with preferred crystal orientation and favorable crystal geometry for emerging device applications.     

The Role of Chlorine in the Formation Process of “CH3NH3PbI3‐xClx” Perovskite

CH₃NH₃PbI_3‐xCl_x is a commonly used chemical formula to represent the methylammonium lead halide perovskite fabricated from mixed chlorine‐ and iodine‐containing salt precursors. Despite the rapid progress in improving its photovoltaic efficiency, fundamental questions remain regarding the atomic ratio of Cl in the perovskite as well as the reaction mechanism that leads to its formation and crystallization. In this work we investigated these questions through a combination of chemical, morphological, structural and thermal characterizations. The elemental analyses reveal unambiguously the negligible amount of Cl atoms in the CH₃NH₃PbI_3‐xCl_x perovskite. By studying the thermal characteristics of methylammonium halides as well as the annealing process in a polymer/perovskite/FTO glass structure, we show that the formation of the CH₃NH₃PbI_3‐xCl_x perovskite is likely driven by release of gaseous CH₃NH₃Cl (or other organic chlorides) through an intermediate organometal mixed halide phase. Furthermore, the comparative study on CH₃NH₃I/PbCl₂ and CH₃NH₃I/PbI₂ precursor combinations with different molar ratios suggest that the initial introduction of a CH₃NH₃⁺ rich environment is critical to slow down the perovskite formation process and thus improve the growth of the crystal domains during annealing; accordingly, the function of Cl^? is to facilitate the release of excess CH₃NH₃⁺ at a relatively low annealing temperatures.     

Efficient Perovskite Hybrid Solar Cells via Ionomer Interfacial Engineering

The surface of the solution‐processed methylammonium lead tri‐iodide (CH₃NH₃PbI₃) perovskite layer in perovskite hybrid solar cells (pero‐HSCs) tends to become rough during operation, which inevitably leads to deterioration of the contact between the perovskite layer and the charge‐extraction layers. Moreover, the low electrical conductivity of the electron extraction layer (EEL) gives rises to low electron collection efficiency and severe charge carrier recombination, resulting in energy loss during the charge‐extraction and ‐transport processes, lowering the efficiency of pero‐HSCs. To circumvent these problems, we utilize a solution‐processed ultrathin layer of a ionomer, 4‐lithium styrenesulfonic acid/styrene copolymer (LiSPS), to re‐engineer the interface of CH₃NH₃PbI₃ in planar heterojunction (PHJ) pero‐HSCs. As a result, PHJ pero‐HSCs are achieved with an increased photocurrent density of 20.90 mA cm^?2, an enlarged fill factor of 77.80%, a corresponding enhanced power conversion efficiency of 13.83%, high reproducibility, and low photocurrent hysteresis. Further investigation into the optical and electrical properties and the thin‐film morphologies of CH₃NH₃PbI₃ with and without LiSPS, and the photophysics of the pero‐HSCs with and without LiSPS are shown. These demonstrate that the high performance of the pero‐HSCs incorporated with LiSPS can be attributed to the reduction in both the charge carrier recombination and leakage current, as well as more efficient charge carrier collection, filling of the perforations in CH₃NH₃PbI_3, and a higher electrical conductivity of the LiSPS thin layer. These results demonstrate that our method provides a simple way to boost the efficiency of pero‐HSCs.     

High‐Performance Photodetectors Based on Organometal Halide Perovskite Nanonets

The booming development of organometal halide perovskites has prompted the exploration of morphology‐engineering strategies to improve their performance in optoelectronic applications. However, the preparation of optoelectronic devices of perovskites with complex architectures and desirable properties is still highly challenging. Herein, novel CH₃NH₃PbI₃ nanonets and nanobowl arrays are fabricated facilely by using monolayer colloidal crystal (MCC) templates on different substrates. Specifically, highly ordered CH₃NH₃PbI₃ nanonets with high crystallinity are fabricated on a variety of flat substrates, whereas regular CH₃NH₃PbI₃ nanobowl arrays are produced on a coarse substrate. The photodetection performance of the CH₃NH₃PbI₃ nanonet‐based photodetectors is significantly enhanced compared to the photodetectors based on conventional CH₃NH₃PbI₃ compact films. Particularly, the nanonet photodetectors exhibit a high responsivity (10.33 A W^?1 under 700 nm monochromatic light), which is six times higher than that for the compact CH₃NH₃PbI₃ film devices, fast response speed, and good stability. Owing to the two‐dimensional arrayed structure, the CH₃NH₃PbI₃ nanonets exhibit an enhanced light harvesting ability and offer direct carrier transport pathways. Meanwhile, the MCC template brings about larger grain sizes with enhanced crystallinity. Furthermore, the perovskite nanonets can be formed on a flexible polyethylene terephthalate substrate for the fabrication of promising flexible nanonet photodetectors.     

Thin Films of Dendritic Anatase Titania Nanowires Enable Effective Hole‐Blocking and Efficient Light‐Harvesting for High‐Performance Mesoscopic Perovskite Solar Cells

To achieve high‐performance perovskite solar cells, especially with mesoscopic cell structure, the design of the electron transport layer (ETL) is of paramount importance. Highly branched anatase TiO₂ nanowires (ATNWs) with varied orientation are grown via a facile one‐step hydrothermal process on a transparent conducting oxide substrate. These films show good coverage with optimization obtained by controlling the hydrothermal reaction time. A homogeneous methyl­ammonium lead iodide (CH₃NH₃PbI₃) perovskite thin film is deposited onto these ATNW films forming a bilayer architecture comprising of a CH₃NH₃PbI₃ sensitized ATNW bottom layer and a CH₃NH₃PbI₃ capping layer. The formation, grain size, and uniformity of the perovskite crystals strongly depend on the degree of surface coverage and the thickness of the ATNW film. Solar cells constructed using the optimized ATNW thin films (220 nm in thickness) yield power conversion efficiencies up to 14.2% with a short‐circuit photocurrent density of 20.32 mA cm^?2, an open‐circuit photovoltage of 993 mV, and a fill factor of 0.70. The dendritic ETL and additional perovskite capping layer efficiently capture light and thus exhibit a superior light harvesting efficiency. The ATNW film is an effective hole‐blocking layer and efficient electron transport medium for excellent charge separation and collection within the cells.     

High‐Performance Flexible Broadband Photodetector Based on Organolead Halide Perovskite

Organolead halide perovskites have attracted extensive attentions as light harvesting materials for solar cells recently, because of its high charge‐carrier mobilities, high photoconversion efficiencies, low energy cost, ease of deposition, and so on. Herein, with CH₃NH₃PbI₃ film deposited on flexible ITO coated substrate, the first organolead halide perovskite based broadband photodetector is demonstrated. The organolead halide perovskite photodetector is sensitive to a broadband wavelength from the ultraviolet light to entire visible light, showing a photo‐responsivity of 3.49 A W^?1, 0.0367 A W^?1, an external quantum efficiency of 1.19×10³%, 5.84% at 365 nm and 780 nm with a voltage bias of 3 V, respectively. Additionally, the as‐fabricated photodetector exhibit excellent flexibility and robustness with no obvious variation of photocurrent after bending for several times. The organolead halide perovskite photodetector with high sensitivity, high speed and broad spectrum photoresponse is promising for further practical applications. And this platform creates new opportunities for the development of low‐cost, solution‐processed and high‐efficiency photodetectors.     

Impact of Crystal Surface on Photoexcited States in Organic–Inorganic Perovskites

Despite their outstanding photovoltaic performance, organic–inorganic perovskite solar cells still face severe stability issues and limitations in their device dimension. Further development of perovskite solar cells therefore requires a deeper understanding of loss mechanisms, in particular, concerning the origin and impact of trap states. Here, different surface properties of submicrometer sized CH₃NH₃PbI₃ particles are studied as a model system by photoluminescence spectroscopy to investigate the impact of the perovskite crystal surface on photoexcited states. Comparison of single crystals with either isolating or electron‐rich surface passivation indicates the presence of positively charged surface trap states that can be passivated in case of the latter. These surface trap states cause enhanced nonradiative recombination at room temperature, which is a loss mechanism for solar cell performance. In the orthorhombic phase, the origin of multiple emission peaks is identified as the recombination of free and bound excitons, whose population ratio critically depends on trap state properties. The dynamics of exciton trapping at 50 K are observed on a time‐scale of tens of picoseconds by a simultaneous population decrease and increase of free and bound excitons, respectively. These results emphasize the potential of surface passivation to further improve the performance of perovskite solar cells.     

Layered Germanium Hybrid Perovskite Bromides: Insights from Experiments and First‐Principles Calculations

Metal halide perovskites are maturing as materials for efficient, yet low cost solar cells and light‐emitting diodes, with improving operational stability and reliability. To date however, most perovskite‐based devices contain Pb, which poses environmental concerns due to its toxicity; lead‐free alternatives are of importance to facilitate the development of perovskite‐based devices. Here, the germanium‐based Ruddledsen–Popper series (CH₃(CH₂)₃NH₃)₂(CH₃NH₃)_n?1Ge_nBr_3n+1 is investigated, derived from the parent 3D (n = ∞) CH₃NH₃GeBr₃ perovskite. Divalent germanium is a promising, nontoxic alternative to Pb²⁺ and the layered, 2D structure appears promising to bolster light emission, long‐term durability, and moisture tolerance. The work, which combines experiments and first principle calculations, highlights that in germanium bromide perovskites the optical bandgap is weakly affected by 2D confinement and the highly stereochemically active 4s² lone pair preludes to possible ferroelectricity, a topic still debated in Pb‐containing compounds.     

Nonlinear Absorption Applications of CH3NH3PbBr3 Perovskite Crystals

Researchers have recently revealed that hybrid lead halide perovskites exhibit ferroelectricity, which is often associated with other physical characteristics, such as a large nonlinear optical response. In this work, the nonlinear optical properties of single crystal inorganic–organic hybrid perovskite CH₃NH₃PbBr₃ are studied. By exciting the material with a 1044 nm laser, strong two‐photon absorption‐induced photoluminescence in the green spectral region is observed. Using the transmission open‐aperture Z‐scan technique, the values of the two‐photon absorption coefficient are observed to be 8.5 cm GW^?1, which is much higher than that of standard two‐photon absorbing materials that are industrially used in nonlinear optical applications, such as lithium niobate (LiNbO₃), LiTaO₃, KTiOPO₄, and KH₂PO₄. Such a strong two‐photon absorption effect in CH₃NH₃PbBr₃ can be used to modulate the spectral and spatial profiles of laser pulses, as well as to reduce noise, and can be used to strongly control the intensity of incident light. In this study, the superior optical limiting, pulse reshaping, and stabilization properties of CH₃NH₃PbBr₃ are demonstrated, opening new applications for perovskites in nonlinear optics.     

Organic–Inorganic Perovskite Light‐Emitting Electrochemical Cells with a Large Capacitance

While perovskite light‐emitting diodes typically made with high work function anodes and low work function cathodes have recently gained intense interests. Perovskite light‐emitting devices with two high work function electrodes with interesting features are demonstrated here. Firstly, electroluminescence can be easily obtained from both forward and reverse biases. Secondly, the results of impedance spectroscopy indicate that the ionic conductivity in the iodide perovskite (CH₃NH₃PbI₃) is large with a value of ≈10^?8 S cm^?1. Thirdly, the shift of the emission spectrum in the mixed halide perovskite (CH₃NH₃PbI_3?xBr_x) light‐emitting devices indicates that I^? ions are mobile in the perovskites. Fourthly, this work shows that the accumulated ions at the interfaces result in a large capacitance (≈100 μF cm^?2). The above results conclusively prove that the organic–inorganic halide perovskites are solid electrolytes with mixed ionic and electronic conductivity and the light‐emitting device is a light‐emitting electrochemical cell. The work also suggests that the organic–inorganic halide perovskites are potential energy‐storage materials, which may be applicable in the field of solid‐state supercapacitors and batteries.     

Synergistic Effect of PbI2 Passivation and Chlorine Inclusion Yielding High Open‐Circuit Voltage Exceeding 1.15 V in Both Mesoscopic and Inverted Planar CH3NH3PbI3(Cl)‐Based Perovskite Solar Cells

Enhancing open‐circuit voltage in CH₃NH₃PbI₃(Cl) perovskite solar cells has become a major challenge for approaching the theoretical limit of the power conversion efficiency. Here, for the first time, it is demonstrated that the synergistic effect of PbI₂ passivation and chlorine incorporation via controlling the molar ratio of PbI₂, PbCl₂ (or MACl), and MAI in the precursor solutions, boosts the open‐circuit voltage of CH₃NH₃PbI₃(Cl) perovskite solar cells over 1.15 V in both mesoscopic and inverted planar perovskite solar cells. Such high open‐circuit voltage can be attributed to the enhanced photoluminescence emission and carrier lifetime associated with the reduced trap densities. The morphology and composition analysis using scanning electron microscopy, X‐ray diffraction measurements, and energy dispersive X‐ray spectroscopy confirm the high quality of the optimized CH₃NH₃PbI₃(Cl) perovskite film. On this basis, record‐high efficiencies of 16.6% for nonmetal‐electrode all‐solution‐processed perovskite solar cells and 18.4% for inverted planar perovskite solar cells are achieved.     

Function Follows Form: Correlation between the Growth and Local Emission of Perovskite Structures and the Performance of Solar Cells

Understanding the relationship between the growth and local emission of hybrid perovskite structures and the performance of the devices based on them demands attention. This study investigates the local structural and emission features of CH₃NH₃PbI₃, CH₃NH₃PbBr₃, and CH(NH₂)₂PbBr₃ perovskite films deposited under different yet optimized conditions using X‐ray scattering and cathodoluminescence spectroscopy, respectively. X‐ray scattering shows that a CH₃NH₃PbI₃ film involving spin coating of CH₃NH₃I instead of dipping is composed of perovskite structures exhibiting a preferred orientation with [202] direction perpendicular to the surface plane. The device based on the CH₃NH₃PbI₃ film composed of oriented crystals yields a relatively higher photovoltage. In the case of CH₃NH₃PbBr₃, while the crystallinity decreases when the HBr solution is used in a single‐step method, the photovoltage enhancement from 1.1 to 1.46 V seems largely stemming from the morphological improvements, i.e., a better connection between the crystallites due to a higher nucleation density. Furthermore, a high photovoltage of 1.47 V obtained from CH(NH₂)₂PbBr₃ devices could be attributed to the formation of perovskite films displaying uniform cathodoluminescence emission. The comparative analysis of the local structural, morphological, and emission characteristics of the different perovskite films supports the higher photovoltage yielded by the relatively better performing devices.     

Controlled Growth and Reliable Thickness‐Dependent Properties of Organic–Inorganic Perovskite Platelet Crystal

Organolead halide perovskites (e.g., CH₃NH₃PbI₃) have caught tremendous attention for their excellent optoelectronic properties and applications, especially as the active material for solar cells. Perovskite crystal quality and dimension is crucial for the fabrication of high‐performance optoelectronic and photovoltaic devices. Herein the controlled synthesis of organolead halide perovskite CH₃NH₃PbI₃ nanoplatelets on SiO₂/Si substrates is investigated via a convenient two‐step vapor transport deposition technique. The thickness and size of the perovskite can be well‐controlled from few‐layers to hundred nanometers by altering the synthesis time and temperature. Raman characterizations reveal that the evolutions of Raman peaks are sensitive to the thickness. Furthermore, from the time‐resolved photoluminescence measurements, the best optoelectronic performance of the perovskite platelet is attributed with thickness of ≈30 nm to its dominant longest lifetime (≈4.5 ns) of perovskite excitons, which means lower surface traps or defects. This work supplies an alternative to the synthesis of high‐quality organic perovskite and their possible optoelectronic applications with the most suitable materials.