Modulation of Buried Interface by 1-(3-aminopropyl)-Imidazole for Efficient Inverted Formamidinium-Cesium Perovskite Solar Cells.

Considering the direct influence of substrate surface nature on perovskite (PVK) film growth, buried interfacial engineering is crucial to obtain ideal perovskite solar cells (PSCs). Herein, 1-(3-aminopropyl)-imidazole (API) is introduced at polytriarylamine (PTAA)/PVK interface to modulate the bottom property of PVK. First, the introduction of API improves the growth of PVK grains and reduces the Pb2+ defects and residual PbI2 present at the bottom of the film, contributing to the acquisition of high-quality PVK film. Besides, the presence of API can optimize the energy structure between PVK and PTAA, which facilitates the interfacial charge transfer. Density functional theory (DFT) reveals that the electron donor unit (R-C ═ N) of the API prefers to bind with Pb2+ traps at the PVK interface, while the formation of hydrogen bonds between the R-NH2 of API and I- strengthens the above binding ability. Consequently, the optimum API-treated inverted formamidinium-cesium (FA/Cs) PSCs yields a champion power conversion efficiency (PCE) of 22.02% and exhibited favorable stability.

Passivating Defects at the Bottom Interface of Perovskite by Ethylammonium to Improve the Performance of Perovskite Solar Cells.

The interface of perovskite solar cells (PSCs) plays a significant role in influencing their performance, yet there is still scarce research focusing on their difficult-to-expose bottom interfaces. Herein, ethylammonium bromide (EABr) is introduced into the bottom interface and its passivation effects are studied directly. First, EABr can improve substrate wettability, which is beneficial for the perovskite-film deposition. By lifting off the perovskite film spontaneously from the substrate, it is found that EABr can significantly reduce the amount of unreacted PbI2 at the bottom interface. These PbI2 crystals have been recently identified as a major defect source and degradation site for perovskite film. Meanwhile, EABr also lifts the valence band maximum at the bottom side of perovskite from -5.38 to -5.09 eV, facilitating better hole transfer. Such a improvement is also verified by the study of charge carrier dynamics. Through introducing EABr, all photovoltaic parameters of the inverted PSCs are improved, and their power conversion efficiency (PCE) increases from 20.41% to 21.06%. The study highlights the importance of direct characterization of the bottom interface for a better passivation effect.