Performance of perovskite solar cells based on SnO₂: DPEPO hybrid electron transport layer

Abstract

The electron transport layer is an important functional layer of perovskite solar cells, and its surface and internal defects are critical parts of limiting the performance improvement of perovskite solar cells. The double electron transport layer (double ETL) strategy enables effective passivation of the inherent defects in the electron transport layer (e.g., SnO₂) and improves the extraction and transport of electrons between the functional layers, which provides an effective way for the development of high-efficiency and stable PSCs. However, due to the existence of independent interfaces within the dual ETL, the issue of cell mismatch of different ETL materials also leads to additional carrier defects, impeding the ongoing advancement of the dual ETL strategy.This work proposes a strategy to introduce di[2-((oxo) diphenylphosphino) phenyl]ether (DPEPO) into SnO₂ ETL to design a hybrid electron transport layer strategy. Taking advantage of DPEPO's hole-blocking effect with higher HOMO energy levels and good electron transport ability, it successfully passivates the intrinsic defects in SnO₂, while significantly improving the crystalline quality of the surface of the SnO₂ film. So, avoiding the direct contact between the perovskite photoactive layer and the conductive substrate, which effectively improves the extraction and transport of electrons. Due to the preparation of high-quality electron transport layer, the crystalline regulation of perovskite thin film was further achieved to enhance the performance of perovskite solar cells, which finally harvested a power conversion rate of 21.53%, in which the open-circuit voltage (V_OC) reached 1.220 V, the short-circuit current (J_SC) was 23.19 mA/cm², and the fill factor (FF) was 76.11%. This efficiency is 1.39% higher than that of the control one. It is shown that the hybrid electron transport layer strategy can not only optimize the carrier transport dynamics efficiently and significantly reduce the device performance affected by the defects in the functional layer, but also regulate the perovskite crystallization, which is promising for the preparation of high-performance solar cells.