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A polaron model of electron-excess color centers in ionic crystals is formulated from the many-particle point of view. This is done by adopting the concepts of the electronic polaron and lattice polaron. We have used our theoretical results and some recent experimental results to give a critical analysis of the semicontinuum model and the dielectric-continuum-effective-mass model of electron-excess centers. The theory also provides a criterion for choosing the so-called dielectric constant appearing in these models.

Self‐assemble monolayer (SAM) has been proven to be an effective interfacial layer to improve the performance of perovskite solar cells (PSCs). Herein, a 3‐mercaptopropyltrimethoxysilane (MPTMS) SAM is used as an interlayer between the SnO2 electron‐transporting layer (ETL) and the perovskite film to modify fully air‐processed PSCs. In the devices prepared by the two‐step method, this MPTMS SAM interlayer can slow down the crystal growth of perovskite and smooth the surface of the SnO2 ETL, which could induce a high‐quality perovskite absorber. In contrast, it can passivate the SnO2/perovskite interface to enhance the extraction efficiency of photogenerated electrons and restrain carrier recombination. As a result, with suitable MPTMS SAM modification, the average power conversion efficiency (PCE) of the fully air‐processed PSCs is significantly improved from 16.62% to 18.75%, and the best device achieved a champion PCE over 20%. Moreover, the modified PSCs exhibit a good stability in ambient air. This research shows that the interface modification of MPTMS SAM is a feasible method for high‐performance PSCs.