Since the first introduction of the organic–inorganic hybrid perovskite in the field of optoelectronics, extraordinary progress in both the photoelectric-conversion-efficiency and stability of perovskite solar cells (PSCs) have been witnessed. However, a variety of drawbacks associated with defects in PSCs, such as energy deficits, ion migration, operational instability and hysteresis, greatly hinder the potential industrial applications of PSCs. Herein, a systematic and comprehensive understanding of the origin, classification, nature, relationships and overlapping effects of defects in perovskite is summarized and reviewed. According to their positions in the energy structure relative to band edges, shallow- and deep-level defects are summarized, while point defects, undercoordinated ions, impurities and pinholes are categorized based on a dimension-criterion. We look at the established understanding of how the detrimental defects induce non-radiative recombination, charge trapping and scattering, ion migration and hysteresis, providing a relatively clear relationship between the performance and defects in perovskite films. An overview of the defect passivation strategies is presented on the fabrication route, including film formation, post-treatment and interlayer engineering between the perovskite layer and charge transport layer, giving a unique perspective. Based on defect passivation engineering, challenges and suggestions to break the bottlenecks of PSCs on the way to commercialization are proposed.

Defect passivation strategies in perovskites for an enhanced photovoltaic performance

The surface of a semiconductor often has a key role in determining its properties. For metal halide perovskites, understanding the surface features and their impact on the materials and devices is becoming increasingly important. At length scales down to the nanoscale regime, surface features become dominant in regulating the properties of perovskite materials, owing to the high surface-to-volume ratio. For perovskite bulk films in the micrometre range, defects and structural disorder readily form at the surface and affect device performance. Through concerted efforts to optimize processing techniques, high-quality perovskite thin films can now be fabricated with monolayer-like polycrystalline grains or even single crystals. Surface defects therefore remain the major obstacle to progress, pushing surface studies to the forefront of perovskite research. In this Review, we summarize and assess recent advances in the understanding of perovskite surfaces and surface strategies towards improving perovskite materials and the efficiency and stability of perovskite devices. The surface features of metal halide perovskites have a crucial role in determining their properties. This Review introduces the recent advances in the understanding of perovskite surfaces and surveys the surface strategies towards improving the properties of perovskite materials and the performance of perovskite optoelectronic devices.

The surface of halide perovskites from nano to bulk

Modeling of highly efficient and low cost CH3NH3Pb(I1-xClx)3 based perovskite solar cell by numerical simulation

Barrier Designs in Perovskite Solar Cells for Long-Term Stability

Zinc oxide (ZnO) based nanostructures have gained remarkable attention worldwide for their photocatalytic activation behavior as a semi-conductor metal oxide photocatalyst in different industries, ...

Synthesis and applications of ZnO nanostructures (ZONSs): a review

Efficient and stable perovskite solar cells thanks to dual functions of oleyl amine-coated PbSO4(PbO)4 quantum dots: Defect passivation and moisture/oxygen blocking

To improve the charge separation and transport efficiency in perovskite solar cells (PSCs) with a TiO2-based hybrid mesoscopic/planar architecture, CdS and Cd(SCN2H4)2Cl2 are incorporated into the CH3NH3PbI3 active layer through in situ synthesis to prepare CdS:Cd(SCN2H4)2Cl2:CH3NH3PbI3 bulk-heterojunction films for PSCs. The incorporated CdS and Cd(SCN2H4)2Cl2 improve the quality of perovskite films. Moreover, Cd(SCN2H4)2Cl2 can effectively reduce the defect state density on the CH3NH3PbI3 crystal surface, which decreases charge recombination and facilitates charge transport in PSCs. Furthermore, first-principles calculations show that the I atom of CH3NH3PbI3 has a strong interaction with the Cd atom of CdS, which induces interfacial charge redistribution and charge transfer at the CH3NH3PbI3/CdS interface and therefore decreases the energy of the CH3NH3PbI3:CdS composite system, leading to more efficient electron–hole separation and improved structural stability of the perovskite bulk-heterojunction film. For the above reasons, the CdS:Cd(SCN2H4)2Cl2:CH3NH3PbI3 bulk-heterojunction cell shows much higher efficiency and better stability than the PSCs with pure CH3NH3PbI3. The highest efficiency reaches 20.1%, which is 1.16 times that (17.3%) of the PSCs with pure CH3NH3PbI3 and is also much higher than those of previously reported CH3NH3PbI3 PSCs with a compact/mesoporous TiO2 film. Our research results may provide a new understanding for improving the structural stability and performance of PSCs.

Enhancing the efficiency and stability of perovskite solar cells by incorporating CdS and Cd(SCN2H4)2Cl2 into the CH3NH3PbI3 active layer

Enhancing the performance of inverted perovskite solar cells by inserting a ZnO:TIPD film between PCBM layer and Ag electrode

We report a new method as UV treatment of low-temperature processed to obtain tin oxide (SnO2) electron transport layers (ETLs). The results show that the high quality of ETLs can be produced by controlling the thickness of the film while it is treated by UV. The thickness is dependent on the concentration of SnO2. Moreover, the conductivity and transmittance of the layer are dependent on the quality of the film. A planar perovskite solar cell is prepared based on this UV-treated film. The temperatures involved in the preparation process are less than 90 °C. An optimal power conversion efficiency of 14.36% is obtained at the concentration of SnO2 of 20%. This method of UV treatment SnO2 film at low temperature is suitable for the low-cost commercialized application.

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UV Treatment of Low-Temperature Processed SnO 2 Electron Transport Layers for Planar Perovskite Solar Cells

An excellent organolead halide perovskite film is important for the good performance of perovskite solar cells (PSCs). However, defects in perovskite crystals can affect the photovoltaic properties and stability of solar cells. To solve this problem, this study incorporated a complex of CdS and Cd(SCN 2 H 4 ) 2 Cl 2 into the CH 3 NH 3 PbI 3 active layer. The effects of different doping concentrations of CdS and Cd(SCN 2 H 4 ) 2 Cl 2 on the performance and stability of PSCs were analyzed. Results showed that doping appropriate incorporation concentrations of CdS and Cd(SCN 2 H 4 ) 2 Cl 2 in CH 3 NH 3 PbI 3 can improve the performance of the prepared solar cells. In specific, CdS and Cd(SCN 2 H 4 ) 2 Cl 2 can effectively passivate the defects in perovskite crystals, thereby suppressing the charge recombination in PSCs and promoting the charge extraction at the TiO 2 /perovskite interface. Due to the reduction of perovskite crystal defects and the enhancement of compactness of the CdS:Cd(SCN 2 H 4 ) 2 Cl 2 :CH 3 NH 3 PbI 3 composite film, the stability of PSCs is significantly improved.

Liangxin Zhu

Papers

Efficient and stable perovskite solar cells thanks to dual functions of oleyl amine-coated PbSO4(PbO)4 quantum dots: Defect passivation and moisture/oxygen blocking

Enhancing the efficiency and stability of perovskite solar cells by incorporating CdS and Cd(SCN2H4)2Cl2 into the CH3NH3PbI3 active layer

Enhancing the performance of inverted perovskite solar cells by inserting a ZnO:TIPD film between PCBM layer and Ag electrode

UV Treatment of Low-Temperature Processed SnO 2 Electron Transport Layers for Planar Perovskite Solar Cells

Effects of the incorporation amount of CdS and Cd(SCN 2 H 4 ) 2 Cl 2 on the performance of perovskite solar cells