n-Type branched shoulder-chain small molecule electron transport layer for inverted perovskite solar cells

Abstract

The electron transport layer (ETL) is a major component of inverted perovskite solar cells (PSCs). It is an effective method for preparing efficient and stable organic ETLs to solve problems such as poor interface contact, adverse energy-level matching, and the lack of a significant passivation effect on perovskites. In this work, two structurally similar n-type branched shoulder-chain small molecules, CY3 and CY4, incorporating [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM), were established as ETLs for inverted PSCs. The results of experimental tests showed that CY3 and CY4 could effectively passivate electron vacancy defects in perovskites, optimize the energy level alignment between the layers of the PSCs, and significantly improve the interface contact between the ETL and the perovskite layer. Consequently, the PSCs with PCBM:CY4 as the ETL achieved a high power conversion efficiency (PCE) of 19.80% and a stability of 760 h in an air atmosphere, compared to PCBM:CY3 (18.78%, 620 h). Our results provide theoretical guidance and a foundation for constructing high-performance ETLs.