Inorganic halide perovskites (IHPs) have recently attracted huge attention in the field of optoelectronics. IHPs are generally expected to exhibit superior chemical stability over the prevailing hybrid organic–inorganic perovskites that are widely used in optoelectronic devices such as solar cells and light-emitting devices. This is primarily owing to the elimination of weakly-bonded organic components in the IHP crystal structure. Nevertheless, many recent studies have revealed that IHPs still suffer significant issues in chemical instability, and thus, a lot of effort has been made towards the stabilization of IHPs for high-performance devices. In this context, a great deal of interest in the chemistry and perovskite community has been emerging to understand the chemical (in)stability of IHPs and develop engineering strategies for making more robust perovskite devices. This review will summarize the past research progress in this direction, give insights into the IHP (in)stability, and provide perspectives for the future effort in making stable IHP materials and devices.

Chemical stability and instability of inorganic halide perovskites

All-inorganic perovskites are considered to be one of the most appealing research hotspots in the field of perovskite photovoltaics in the past 3 years due to their superior thermal stability compared to their organic-inorganic hybrid counterparts. The power-conversion efficiency has reached 17.06% and the number of important publications is ever increasing. Here, the progress of inorganic perovskites is systematically highlighted, covering materials design, preparation of high-quality perovskite films, and avoidance of phase instabilities. Inorganic perovskites, nanocrystals, quantum dots, and lead-free compounds are discussed and the corresponding device performances are reviewed, which have been realized on both rigid and flexible substrates. Methods for stabilization of the cubic phase of low-bandgap inorganic perovskites are emphasized, which is a prerequisite for highly efficient and stable solar cells. In addition, energy loss mechanisms both in the bulk of the perovskite and at the interfaces of perovskite and charge selective layers are unraveled. Reported approaches to reduce these charge-carrier recombination losses are summarized and complemented by methods proposed from our side. Finally, the potential of inorganic perovskites as stable absorbers is assessed, which opens up new perspectives toward the commercialization of inorganic perovskite solar cells.

Review on Recent Progress of All-Inorganic Metal Halide Perovskites and Solar Cells.

Untapped Potentials of Inorganic Metal Halide Perovskite Solar Cells

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High-Performance Flexible Perovskite Solar Cells via Precise Control of Electron Transport Layer

Interface engineering of low temperature processed all-inorganic CsPbI2Br perovskite solar cells toward PCE exceeding 14%

Highly efficient CsPbI2Br planar heterojunction (PHJ) perovskite solar cells (PSCs) with a structure of ITO/SnO2/CsPbI2Br/Spiro-OMeTAD/Ag are fabricated via a low-temperature solution process. A flash annealing technique is used to produce high-quality CsPbI2Br perovskite films with high density and uniformity, as well as highly crystallized CsPbI2Br films. These CsPbI2Br films are used as the light-harvesting layer in PHJ PSC devices using SnO2 as the electron transport layer and Spiro-OMeTAD as the hole transport layer. Based on the measurement of the energy levels via ultraviolet photoelectron spectroscopy, it indicates that there is a very good interfacial band alignment between SnO2 and CsPbI2Br, supporting the efficient electron extraction from CsPbI2Br to SnO2. Thus, simple structural CsPbI2Br PHJ PSCs with power conversion efficiencies (PCEs) up to 13.09% are achieved, which is comparable to the highest reported PCEs for all-inorganic PHJ PSCs. The findings show that the PHJ device architecture, i...

Highly Efficient, Solution-Processed CsPbI2Br Planar Heterojunction Perovskite Solar Cells via Flash Annealing

Efficient and stable planar heterojunction perovskite solar cells fabricated under ambient conditions with high humidity

Organic solar cells (OSCs) have been attracting considerable interest due to their unique advantages of low cost, light weight, and especially mechanical flexibility. The low-cost and high-throughput techniques matching with the large-scale and roll-to-roll (R2R) process for fabricating efficient OSCs in the ambient condition would greatly accelerate the potential commercialization of OSCs. Herein, we demonstrate that the fabrication processes of OSCs using the bulk heterojunction (BHJ) composed of poly[(2,6–(4,8-bis(5–(2-ethylhexy)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5–(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′5′-c′]dithiophene-4,8-dione))] (PBDB-T) and 3,9-bis(2-methylene-(3–(1,1-dicyanomethylene)-5-methylindanone)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]-dithiophene (IT-M) are transferred from a glovebox to the ambient condition, where the deposition of doctor blading instead of conventional spin coating is investigated. The morphology, microphase separation, and crystallinity of BHJ PBDB-T:IT-M are dramatically influenced by the fabrication processes. The OSCs with a structure of ITO/ZnO/PBDB-T:IT-M/MoO3/Ag fabricated via doctor-blading in the ambient condition show a power conversion efficiency (PCE) of 9.0% as compared to conventional spin-coated OSCs in a glovebox with a PCE of 11.91% and in the ambient condition with a PCE of 9.91%. These results suggest that efficient OSCs could be processed in the ambient condition by large-scale and low-cost doctor-blading, which can be compatible with the R2R manufacturing process.

Yanan Dong

Papers

Highly Efficient, Solution-Processed CsPbI2Br Planar Heterojunction Perovskite Solar Cells via Flash Annealing

Efficient and stable planar heterojunction perovskite solar cells fabricated under ambient conditions with high humidity

Efficient organic solar cells with the active layer fabricated from glovebox to ambient condition

Highly selective and rapid removal of metal ions from ionic liquids solutions through size-sieving and ion-exchange strategy