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CsPbI₂Br perovskite is doped by Eu(Ac)₃ to obtain high‐quality perovskite films with low defect density and long carrier lifetime. A high efficiency of 15.25%, an open‐circuit voltage of 1.25 V, a short‐circuit current density of 15.44 mA cm⁻², and a fill factor of 79.00% are realized for CsPbI₂Br solar cells. The devices with Eu(Ac)₃ doping demonstrate excellent air stability.

Abstract

All‐inorganic perovskite solar cells have developed rapidly in the last two years due to their excellent thermal and light stability. However, low efficiency and moisture instability limit their future commercial application. The mixed‐halide inorganic CsPbI₂Br perovskite with a suitable bandgap offers a good balance between phase stability and light harvesting. However, high defect density and low carrier lifetime in CsPbI₂Br perovskites limit the open‐circuit voltage (V _oc < 1.2 V), short‐circuit current density (J _sc < 15 mA cm⁻²), and fill factor (FF < 75%) of CsPbI₂Br perovskite solar cells, resulting in an efficiency below 14%. For the first time, a CsPbI₂Br perovskite is doped by Eu(Ac)₃ to obtain a high‐quality inorganic perovskite film with a low defect density and long carrier lifetime. A high efficiency of 15.25% (average efficiency of 14.88%), a respectable V _oc of 1.25 V, a reasonable J _sc of 15.44 mA cm⁻², and a high FF of 79.00% are realized for CsPbI₂Br solar cells. Moreover, the CsPbI₂Br solar cells with Eu(Ac)₃ doping demonstrate excellent air stability and maintain more than 80% of their initial power conversion efficiency (PCE) values after aging in air (relative humidity: 35–40%) for 30 days.

Low‐cost n‐type goethite (FeOOH) quantum dots (QDs) are introduced into the perovskite light‐absorber layer to fabricate efficient and stable perovskite solar cells (PSCs). As a result, the PSCs with FeOOH QDs obtain a significant efficiency enhancement from 16.6% to 19.7%. Most strikingly, the long‐term stability of PSCs with FeOOH QDs is significantly enhanced.

Abstract

Minimization of defects and ion migration in organic–inorganic lead halide perovskite films is desirable for obtaining photovoltaic devices with high power conversion efficiency (PCE) and long‐term stability. However, achieving this target is still a challenge due to the lack of efficient multifunctional passivators. Herein, to address this issue, n‐type goethite (FeOOH) quantum dots (QDs) are introduced into the perovskite light‐absorption layer for achieving efficient and stable perovskite solar cells (PSCs). It is found that the iron, oxygen, and hydroxyl of FeOOH QDs can interact with iodine, lead, and methylamine, respectively. As a result, the crystallization kinetics process can be retarded, thereby resulting in high quality perovskite films with large grain size. Meanwhile, the trap states of perovskite can be effectively passivated via interaction with the under‐coordinated metal (Pb) cations, halide (I) anions on the perovskite crystal surface. Consequently, the PSCs with FeOOH QDs achieve a high efficiency close to 20% with negligible hysteresis. Most strikingly, the long‐term stability of PSCs is significantly enhanced. Furthermore, compared with the CH₃NH₃PbI₃‐based device, a higher PCE of 21.0% is achieved for the device assembled with a Cs_0.05FA_0.81MA_0.14PbBr_0.45I_2.55 perovskite layer.

The polyelectrolyte‐doped SnO₂ film can efficiently improve the perovskite solar cell (PSC) performance and stability. Compared with the pristine SnO₂ film, the better energy level alignment, larger built‐in field, enhanced electron transfer/extraction, and reduced charge recombination all contribute to the improved device performance. Finally, a power conversion efficiency of 20.61% is successfully achieved for the PSC prepared under low temperature.

The charge transport layer is crucial to the performance and stability of the perovskite solar cells (PSCs). Compared with other conventional metal oxide electron transport materials, SnO₂ has a deeper conduction band and higher electron mobility, and can efficiently serve as an electron transport layer to facilitate charge extraction and transfer. Herein, an optimized low‐temperature solution‐processed SnO₂ electron transport layer is achieved by doping polyethylenimine polyelectrolyte into SnO₂ for the first time in the PSCs. It is found that the performance of all aspects of the doped SnO₂ film is improved over that of the pristine SnO₂ film. The better energy level alignment, larger built‐in field, enhanced electron transfer/extraction, and reduced charge recombination all contribute to the improved device performance. Finally, a PSC with a power conversion efficiency of 20.61% is successfully prepared under low temperature below 150 °C. Moreover, the stability of the doped SnO₂‐based device is also greatly improved.

The mechanism of current shunting in flexible Cu₂Zn_1−x Cd _x Sn(S,Se)₄ solar cells is studied. The results demonstrate that partial Cd substitution of Zn can significantly minimize the loss of parallel current (ohmic current, weak diode current, and space‐charge limited current) and enhance fill factor, resulting in a significant improvement in device repeatability (with best efficiency of 6.49%).

Partial cation substitution is an effective way to inhibit defects and carrier recombination, which can improve the efficiency of Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells. Herein, flexible Cu₂Zn_1−x Cd _x Sn(S,Se)₄ (x = 0–15%) solar cells are fabricated on Mo foils with partial Cd substitution for Zn via a green solution‐process. The best device performance can be achieved when Cd/(Zn + Cd) = 8%, with an efficiency up to 6.49% and a significantly improved device repeatability. The E _U decreases from 24 to 15 meV, indicating that antisite defects and band tailings are effectively suppressed. C–V data reveal that W _d and V _bi are enhanced after doping Cd, resulting in a stronger built‐in electric field which facilitates Fermi‐level splitting and hence increases band bending of the absorber toward the junction interface. Furthermore, the mechanism of current shunting is studied using an equivalent circuit model with three parallel current pathways to fit J–V curves. The key parameters for the solar cell diode such as A, J ₀, and R _sh are significantly improved by partially substituting Zn with Cd, demonstrating that current shunting loss is suppressed and the junction quality is improved, resulting in a significant improvement in device repeatability.

Poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) is doped with 0.025 mol% molecular organic Lewis acid bis(pentafluorophenyl)zinc, which exhibits higher hole mobility and well‐matched energy. An enhanced highest power conversion efficiency of 17.49% is achieved for a perovskite solar cell based on doped P3HT without destroying its stability.

The molecular organic Lewis acid bis(pentafluorophenyl)zinc [Zn(C₆F₅)₂] is reported as an efficient p‐type dopant for poly(3‐hexylthiophene‐2,5‐diyl) (P3HT), to be used as hole‐transporting material (HTM) in perovskite solar cells (PSCs) for the first time. To date, the most efficient PSCs use lithium bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) and 4‐tert‐butylpyridine (tBP) as standard additives for HTMs. However, such dopants can induce deleterious effects on device stability. Herein, the effect of the concentration of Zn(C₆F₅)₂ in P3HT HTM on the performance of PSCs is investigated. The P3HT‐based PSCs using a low concentration of the dopant (0.025 mol%) in the HTM layer exhibit the best performance and the highest power conversion efficiency (PCE) of 17.49%, which is almost 3.5% higher than the achieved PCE for pristine P3HT‐based PSCs. The origin of the improved performance for PSCs is further investigated, by studying the conductivity and hole mobility of the thin films based on pristine and doped P3HT. Adding a small amount of Zn(C₆F₅)₂ to P3HT increases its thin‐film hole mobility and its hole extraction ability.

Zero‐Dimensional Perovskites

In article number 201900127, Xiaosheng Tang, Juan Du, Yuxin Leng, and co‐workers study the photophysical properties of zero‐dimensional Cs₄PbBr₆ by using femtosecond transient absorption measurements; the existence of polarons provides evidence of the inherent green emission from Cs₄PbBr₆. Furthermore, the excellent stable lasing performance at room temperature from Cs₄PbBr₆ perovskite microdisks is successfully achieved.

Machine learning (ML) is used to predict the material bandgap and perovskite solar cell device performances. The findings from the ML model matches well with the trend in the solar cell theory derived from the “Shockley and Queisser limit.” Other findings, which are beneficial for the fabrication of high‐performing perovskite solar cells are also discussed.

Abstract

Perovskite solar cells (PSCs) have recently received considerable attention due to the high energy conversion efficiency achieved within a few years of their inception. However, a machine learning (ML) approach to guide the development of high‐performing PSCs is still lacking. In this paper ML is used to optimize material composition, develop design strategies, and predict the performance of PSCs. The ML models are developed using 333 data points selected from about 2000 peer reviewed publications. These models guide the design of new perovskite materials and the development of high‐performing solar cells. Based on ML guidance, new perovskite compositions are experimentally synthesized to test the practicability of the model. The ML model also shows its ability to predict underlying physical phenomena as well as the performance of PSCs. The PSC model matches well with the theoretical prediction by the Shockley and Queisser limit, which is almost impossible for a human to find from an ensemble of data points. Moreover, strategies for developing high‐performing PSCs with different bandgaps are also derived from the model. These findings show that ML is very promising not only for predicting the performance, but also for providing a deeper understanding of the physical phenomena associated with the PSCs.

Perovskite solar cells still have huge room for improvement in photoelectric conversion efficiency. One of the constraints is the defects at the interface between the perovskite and the transport layer. Passivation is considered a key measure to limit defects. This paper systematically categorizes the effective passivation strategies for perovskites in recent years and gives a future outlook.

Abstract

The disorderly distribution of defects in the perovskite or at the grain boundaries, surfaces, and interfaces, which seriously affect carrier transport through the formation of nonradiative recombination centers, hinders the further improvement on the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Several defect passivation strategies have been confirmed as an efficient approach for promoting the performance of PSCs. Herein, recent progress in the defect passivation toward efficient perovskite solar cells are summarized, and a classification of common passivation strategies that elaborate the mechanism according to the location of the defects and the type of passivation agent is presented. Finally, this review offers likely prospects for future trends in the development of passivation strategies.

The various additives adopted for perovskite solar cells (PSCs) are reviewed and their functioning mechanisms and influence on device performance are described. The main roles of additives modulating morphology of perovskite films are summarized; stabilizing phase of formamidinium and cesium‐based perovskites, adjusting energy level alignment in PSCs, suppressing nonradiative recombination in perovskite, eliminating hysteresis, and enhancing operational stability of PSCs.

Abstract

Additives are widely adopted for efficient, stable, and hysteresis‐free perovskite solar cells and play an important role in various breakthroughs of perovskite solar cells (PSCs). Herein the various additives adopted for PSCs are reviewed and their functioning mechanism and influence on device performance is described. The main roles of additives, modulating morphology of perovskite films, stabilizing phase of formamidinium (FA) and cesium (Cs)‐based perovskites, adjusting energy level alignment in PSCs, suppressing nonradiative recombination in perovskites, eliminating hysteresis, enhancing operational stability of PSCs, are summarized.

The replacement of lead with tin in halide perovskites is feasible due to suitable ionic radius and valency. However, easy oxidation, high cost and toxicity concerns in Sn halide perovskite systems may limit the consideration of Sn as a suitable alternative to Pb.

Abstract

The chemical composition engineering of lead halide perovskites via a partial or complete replacement of toxic Pb with tin has been widely reported as a feasible process due to the suitable ionic radius of Sn and its possibility of existing in the +2 state. Interestingly, a complete replacement narrows the bandgap while a partial replacement gives an anomalous phenomenon involving a further narrowing of bandgap relative to the pure Pb and Sn halide perovskite compounds. Unfortunately, the merits of this anomalous behavior have not been properly harnessed. Although promising progress has been made to advance the properties and performance of Sn‐based perovskite systems, their photovoltaic (PV) parameters are still significantly inferior to those of the Pb‐based analogs. This review summarizes the current progress and challenges in the preparation, morphological and photophysical properties of Sn‐based halide perovskites, and how these affect their PV performance. Although it can be argued that the Pb halide perovskite systems may remain the most sought after technology in the field of thin film perovskite PV, prospective research directions are suggested to advance the properties of Sn halide perovskite materials for improved device performance.

By precisely controlling the film properties of electron transport layer SnO₂, flexible perovskite solar cells with a structure of indium tin oxide/SnO₂/FA_0.945MA_0.025Cs_0.03Pb(I_0.975Br_0.025)₃/Spiro‐OMeTAD/Ag gives a power conversion efficiency of 19.51% and a steady output of 19.01%. The flexible devices present excellent bending resistance and long‐term stability.

Abstract

Flexible perovskite solar cells (f‐PSCs) have attracted great attention due to their promising commercial prospects. However, the performance of f‐PSCs is generally worse than that of their rigid counterparts. Herein, it is found that the unsatisfactory performance of planar heterojunction (PHJ) f‐PSCs can be attributed to the undesirable morphology of electron transport layer (ETL), which results from the rough surface of the flexible substrate. Precise control over the thickness and morphology of ETL tin dioxide (SnO₂) not only reduces the reflectance of the indium tin oxide (ITO) on polyethylene 2,6‐naphthalate (PEN) substrate and enhances photon collection, but also decreases the trap‐state densities of perovskite films and the charge transfer resistance, leading to a great enhancement of device performance. Consequently, the f‐PSCs, with a structure of PEN/ITO/SnO₂/perovskite/Spiro‐OMeTAD/Ag, exhibit a power conversion efficiency (PCE) up to 19.51% and a steady output of 19.01%. Furthermore, the f‐PSCs show a robust bending resistance and maintain about 95% of initial PCE after 6000 bending cycles at a bending radius of 8 mm, and they present an outstanding long‐term stability and retain about 90% of the initial performance after >1000 h storage in air (10% relative humidity) without encapsulation.

Recent case studies demonstrate how probing of local heterogeneities and ensemble averaged properties of perovskites by surface science techniques can help build connections between material properties and perovskite solar cell (PSC) performance. How the generation/healing of electronic defects within the semiconductor band‐gap influences PSC efficiency, lifetime, as well reproducibility is also the central focus of this review article.

Abstract

ABX₃ type metal halide perovskite solar cells (PSCs) have shown efficiencies over 25%, rocketing toward their theoretical limit. To gain the full potential of PSCs relies on the understanding of the device working mechanisms and recombination, the material quality, and the match of energy levels in the device stacks. In this review, the importance of designing PSCs from the viewpoint of surface/interface science studies is presented. For this purpose, recent case studies are discussed to demonstrate how probing of local heterogeneities (e.g., grains, grain boundaries, atomic structure, etc.) in perovskites by surface science techniques can help correlate material properties and PSC device performance. At the solar cell device level with active areas larger than millimeter scale, the ensemble average measurement techniques can characterize the overall average properties of perovskite films as well as their adjacent layers and provide clues to understand better the solar cell parameters. How generation and healing of electronic defects in perovskite films limit the device efficiency, reproducibility, and stability, and induce the time‐dependent transient behavior in the current‐voltage curves are also the central focus of this review. On the basis of these studies, strategies to further improve efficiency and stability, as well as reducing hysteresis are presented.

Replacing a 2,2′,7,7′‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9′‐spirobifluorene hole transporting layer with new alternatives such as poly(5,5‐didecyl‐5H‐1,8‐dithia‐as‐indacenone‐alt‐thieno[3,2‐b]thiophene) in mesoscopic perovskite solar cells reduces the fabrication cost and improves the operational stability without sacrificing the efficiency.

Abstract

Stability is the main challenge in the field of organic–inorganic perovskite solar cells (PSCs). Finding low‐cost and stable hole transporting layer (HTL) is an effective strategy to address this issue. Here, a new donor polymer, poly(5,5‐didecyl‐5H‐1,8‐dithia‐as‐indacenone‐alt‐thieno[3,2‐b]thiophene) (PDTITT), is synthesized and employed as an HTL in PSCs, which has a suitable band alignment with respect to the double‐A cation perovskite film. Using PDTITT, the hole extraction in PSCs is greatly improved as compared to commonly used HTLs such as 2,2′,7,7′‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9′‐spirobifluorene (spiro‐OMeTAD), addressing the hysteresis issue. After careful optimization, an efficient PSC is achieved based on mesoscopic TiO₂ electron transporting layer with a maximum power conversion efficiency (PCE) of 18.42% based on PDTITT HTL, which is comparable with spiro‐OMeTAD‐based PSC (19.21%). Since spiro‐based PSCs suffer from stability issue, the operational stability in the PSC with PDTITT HTL is studied. It is found that the device with PDTITT retains 88% of its initial PCE value after 200 h under illumination, which is better than the spiro‐based PSC (54%).

A general approach for lab‐to‐manufacturing translation is developed to achieve high‐performance flexible organic solar modules without obvious efficiency loss. The shear impulse during the coating/printing process is applied to control the morphology evolution of the bulk heterojunction layer for both fullerene and nonfullerene acceptor systems. A quantitative transformation factor of shear impulse between slot‐die printing and spin‐coating is detected.

Abstract

The blossoming of organic solar cells (OSCs) has triggered enormous commercial applications, due to their high‐efficiency, light weight, and flexibility. However, the lab‐to‐manufacturing translation of the praisable performance from lab‐scale devices to industrial‐scale modules is still the Achilles' heel of OSCs. In fact, it is urgent to explore the mechanism of morphological evolution in the bulk heterojunction (BHJ) with different coating/printing methods. Here, a general approach to upscale flexible organic photovoltaics to module scale without obvious efficiency loss is demonstrated. The shear impulse during the coating/printing process is first applied to control the morphology evolution of the BHJ layer for both fullerene and nonfullerene acceptor systems. A quantitative transformation factor of shear impulse between slot‐die printing and spin‐coating is detected. Compelling results of morphological evolution, molecular stacking, and coarse‐grained molecular simulation verify the validity of the impulse translation. Accordingly, the efficiency of flexible devices via slot‐die printing achieves 9.10% for PTB7‐Th:PC₇₁BM and 9.77% for PBDB‐T:ITIC based on 1.04 cm² . Furthermore, 15 cm² flexible modules with effective efficiency up to 7.58% (PTB7‐Th:PC₇₁BM) and 8.90% (PBDB‐T:ITIC) are demonstrated with satisfying mechanical flexibility and operating stability. More importantly, this work outlines the shear impulse translation for organic printing electronics.

A 0D Cs₄PbI₆/3D CsPbI₃ heterostructure is achieved by tuning the stoichiometry of the precursors. The coexistent Cs₄PbI₆ not only reduces the grain size of the CsPbI₃ and serves as a molecular lock to stabilize the black‐phase CsPbI₃, but also passivates the defects in the grain boundaries and improves the surface coverage to improve the device performance to 16.39%.

Abstract

Although organic–inorganic hybrid perovskite solar cells (PVSCs) have achieved dramatic improvement in device efficiency, their long‐term stability remains a major concern prior to commercialization. To address this issue, extensive research efforts are dedicated to exploiting all‐inorganic PVSCs by using cesium (Cs)‐based perovskite materials, such as α‐CsPbI₃. However, the black‐phase CsPbI₃ (cubic α‐CsPbI₃ and orthorhombic γ‐CsPbI₃ phases) is not stable at room temperature, and it tends to convert to the nonperovskite δ‐CsPbI₃ phase. Here, a simple yet effective approach is described to prepare stable black‐phase CsPbI₃ by forming a heterostructure comprising 0D Cs₄PbI₆ and γ‐CsPbI₃ through tuning the stoichiometry of the precursors between CsI and PbI. Such heterostructure is manifested to enable the realization of a stable all‐inorganic PVSC with a high power conversion efficiency of 16.39%. This work provides a new perspective for developing high‐performance and stable all‐inorganic PVSCs.

Application of the proposed slow post‐annealing for layered 2D perovskite solar cells based on BA₂MA₃Pb₄I₁₃ photo‐absorber leads to a favorable alignment on the multi‐perovskite phases and resultant champion power conversion efficiency to 17.26%, showing simultaneously enhanced open‐circuit voltage and short‐circuit current.

Abstract

Layered Ruddlesden–Popper (RP) phase (2D) halide perovskites have attracted tremendous attention due to the wide tunability on their optoelectronic properties and excellent robustness in photovoltaic devices. However, charge extraction/transport and ultimate power conversion efficiency (PCE) in 2D perovskite solar cells (PSCs) are still limited by the non‐eliminable quantum well effect. Here, a slow post‐annealing (SPA) process is proposed for BA₂MA₃Pb₄I₁₃ (n = 4) 2D PSCs by which a champion PCE of 17.26% is achieved with simultaneously enhanced open‐circuit voltage, short‐circuit current, and fill factor. Investigation with optical spectroscopy coupled with structural analyses indicates that enhanced crystal orientation and favorable alignment on the multiple perovskite phases (from the 2D phase near bottom to quasi‐3D phase near top regions) is obtained with SPA treatment, which promotes carrier transport/extraction and suppresses Shockley–Read–Hall charge recombination in the solar cell. As far as it is known, the reported PCE is so far the highest efficiency in RP phase 2D PSCs based on butylamine (BA) spacers (n = 4). The SPA‐processed devices exhibit a satisfactory stability with <4.5% degradation after 2000 h under N₂ environment without encapsulation. The demonstrated process strategy offers a promising route to push forward the performance in 2D PSCs toward realistic photovoltaic applications.

Organic photovoltaic (OPV) cells promise to have a good photovoltaic performance under the indoor light environment. Via optimizing the active layers, 1 cm² OPV cells are fabricated and a top power conversion efficiency of 22% under 1000 lux illumination is demonstrated.

Abstract

Organic photovoltaic (OPV) technologies have the advantages of fabricating larger‐area and light‐weight solar panels on flexible substrates by low‐cost roll‐to‐toll production. Recently, OPV cells have achieved many significant advances with power conversion efficiency (PCE) increasing rapidly. However, large‐scale solar farms using OPV modules still face great challenges, such as device stability. Herein, the applications of OPV cells in indoor light environments are studied. Via optimizing the active layers to have a good match with the indoor light source, 1 cm² OPV cells are fabricated and a top PCE of 22% under 1000 lux light‐emitting diode (2700 K) illumination is demonstrated. In this work, the light intensities are measured carefully. Incorporated with the external quantum efficiency and photon flux spectrum, the integral current densities of the cells are calculated to confirm the reliability of the photovoltaic measurement. In addition, the devices show much better stability under continuous indoor light illumination. The results suggest that designing wide‐bandgap active materials to meet the requirements for the indoor OPV cells has a great potential in achieving higher photovoltaic performance.

The high‐performing single‐junction organic solar cell blend, PM6:Y6, is examined to obtain an in‐depth understanding of the voltage losses, and charge recombination and extraction dynamics. The devices exhibit remarkable extraction coupled with moderate recombination losses. This behavior can most likely be credited to a beneficial morphology as evidenced by atomically resolved ¹⁹F magic‐angle‐spinning solid‐state NMR analysis.

Abstract

The highly efficient single‐junction bulk‐heterojunction (BHJ) PM6:Y6 system can achieve high open‐circuit voltages (V _OC) while maintaining exceptional fill‐factor (FF) and short‐circuit current (J _SC) values. With a low energetic offset, the blend system is found to exhibit radiative and non‐radiative recombination losses that are among the lower reported values in the literature. Recombination and extraction dynamic studies reveal that the device shows moderate non‐geminate recombination coupled with exceptional extraction throughout the relevant operating conditions. Several surface and bulk characterization techniques are employed to understand the phase separation, long‐range ordering, as well as donor:acceptor (D:A) inter‐ and intramolecular interactions at an atomic‐level resolution. This is achieved using photo‐conductive atomic force microscopy, grazing‐incidence wide‐angle X‐ray scattering, and solid‐state ¹⁹F magic‐angle‐spinning NMR spectroscopy. The synergy of multifaceted characterization and device physics is used to uncover key insights, for the first time, on the structure–property relationships of this high‐performing BHJ blend. Detailed information about atomically resolved D:A interactions and packing reveals that the high performance of over 15% efficiency in this blend can be correlated to a beneficial morphology that allows high J _SC and FF to be retained despite the low energetic offset.

In article number https://doi.org/10.1002/adma.2019036491903649, Xiaotian Hu, Wei Ma, Yiwang Chen, and co‐workers report a general approach to upscale flexible organic photovoltaics to the module scale without obvious efficiency loss by calculating the shear impulse during the coating/printing process. Photoelectric conversion efficiencies of 9.77% for a 1 cm² single chip and 8.90% for a 15 cm² solar module are demonstrated. The mechanics of shear impulse link the spin‐coating and slot‐die printing like a small boat overcoming the obstacles of thousands of mountains to arrive at a large‐area printing ferry. This research method also opens up a new strategy of lab‐to‐manufacturing translation for organic optoelectronic devices.

A 0D Cs₄PbI₆/3D CsPbI₃ heterostructure is achieved by tuning the stoichiometry of the precursors. The coexistent Cs₄PbI₆ not only reduces the grain size of the CsPbI₃ and serves as a molecular lock to stabilize the black‐phase CsPbI₃, but also passivates the defects in the grain boundaries and improves the surface coverage to improve the device performance to 16.39%.

Abstract

Although organic–inorganic hybrid perovskite solar cells (PVSCs) have achieved dramatic improvement in device efficiency, their long‐term stability remains a major concern prior to commercialization. To address this issue, extensive research efforts are dedicated to exploiting all‐inorganic PVSCs by using cesium (Cs)‐based perovskite materials, such as α‐CsPbI₃. However, the black‐phase CsPbI₃ (cubic α‐CsPbI₃ and orthorhombic γ‐CsPbI₃ phases) is not stable at room temperature, and it tends to convert to the nonperovskite δ‐CsPbI₃ phase. Here, a simple yet effective approach is described to prepare stable black‐phase CsPbI₃ by forming a heterostructure comprising 0D Cs₄PbI₆ and γ‐CsPbI₃ through tuning the stoichiometry of the precursors between CsI and PbI. Such heterostructure is manifested to enable the realization of a stable all‐inorganic PVSC with a high power conversion efficiency of 16.39%. This work provides a new perspective for developing high‐performance and stable all‐inorganic PVSCs.