Efficient, Hysteresis‐Free, and Stable Perovskite Solar Cells with ZnO as Electron‐Transport Layer: Effect of Surface Passivation

Abstract

The power conversion efficiency of perovskite solar cells (PSCs) has ascended from 3.8% to 22.1% in recent years. ZnO has been well-documented as an excellent electron-transport material. However, the poor chemical compatibility between ZnO and organo-metal halide perovskite makes it highly challenging to obtain highly efficient and stable PSCs using ZnO as the electron-transport layer. It is demonstrated in this work that the surface passivation of ZnO by a thin layer of MgO and protonated ethanolamine (EA) readily makes ZnO as a very promising electron-transporting material for creating hysteresis-free, efficient, and stable PSCs. Systematic studies in this work reveal several important roles of the modification: (i) MgO inhibits the interfacial charge recombination, and thus enhances cell performance and stability; (ii) the protonated EA promotes the effective electron transport from perovskite to ZnO, further fully eliminating PSCs hysteresis; (iii) the modification makes ZnO compatible with perovskite, nicely resolving the instability of ZnO/perovskite interface. With all these findings, PSCs with the best efficiency up to 21.1% and no hysteresis are successfully fabricated. PSCs stable in air for more than 300 h are achieved when graphene is used to further encapsulate the cells.

Low‐Temperature Solution‐Processed ZnO Electron Transport Layer for Highly Efficient and Stable Planar Perovskite Solar Cells with Efficiency Over 20%

“…However, the SAM modification cannot ensure a complete coverage on the ZnO surface, and therefore, the stability cannot be significantly improved. Zheng and co‐authors used a MgO thin layer and protonated ethanolamine (EA) to passivate the ZnO surface readily, and the best PSC with an efficiency of 21.1% and without hysteresis has been successfully fabricated. However, these applied ZnO ETLs cannot be processed at low temperatures due to the residue acetate ligand that could further increase the possibility of decomposition.…”

Activating Old Materials with New Architecture: Boosting Performance of Perovskite Solar Cells with H2O‐Assisted Hierarchical Electron Transporting Layers

“…[7,8] To solve this problem, we previously modified planar TiO 2 ETLs with a thin PC 61 BM buffer layer, and found that the elastic nature of the PC 61 BM could facilitate the formation of high-quality perovskite films and improve the TiO 2 /perovskite interfacial properties. However, a major drawback of planar m-TiO 2 ETLs, which renders them unsuitable for application as PSCs, is that their interfacial charge extraction is insufficiently rapid.…”

Suppressed Decomposition of Perovskite Film on ZnO Via a Self‐Assembly Monolayer of Methoxysilane

“…Despite some promising results, PSCs based on ZnO suffer from severe instability problems, especially thermal instability problem. Perovskite films on ZnO decompose rapidly due to the proton transfer of methylammonium (MA) cation caused by the nature of ZnO surface, and the decomposition is accelerated due to its more violent molecule motion at high temperature . Moreover, there are also a lot of hydroxyl groups or chemical residuals on the low‐temperature process ZnO surface, causing accelerated degradation of perovskite film .…”

“…Zhao et al coated a thin SnO 2 layer onto ZnO nanorods to inhibit the contact between perovskite and ZnO, and improved the performance stability of PSCs dramatically. Zheng et al used an ultra‐thin MgO layer and protonated ethanolamine as the modification materials of ZnO. This modification not only improved the photovoltaic performance, but also enhanced the stability of PSCs.…”