Carbazole-based organic ammonium iodide salts as a versatile interlayer for the HTL/perovskite interface in inverted perovskite solar cells

Abstract

Inverted p-i-n perovskite solar cells (PSCs) have drastically increased in efficiency in recent years, partially due to the inclusion of self-assembling molecules (SAMs) as hole transporting materials (HTLs) and the addition of large organic ammonium salts as a passivating interlayer. In this study, the effect of halogen-functionalized carbazole-based ammonium salts as interlayers between the perovskite absorber and different HTLs is investigated. Fluorinated (F2-Cz), chlorinated (Cl2-Cz), and brominated (Br2-Cz) derivatives are synthesized and incorporated into p-i-n PSCs using NiOx, PTAA, 2PACz, and 4PAPyr as HTLs. All interlayers improve the open-circuit voltage (Voc), indicating effective defect passivation. Notably, a systematic increase in current density (Jsc) and overall PCE is observed across the halogen series from fluorine to bromine. Br2-Cz consistently delivered the highest performance across all tested HTLs, confirming its versatility as an interlayer that is compatible with different types of HTL. The highest power conversion efficiency of 20.9% (0.125 cm2) is achieved when applying the brominated carbazole derivative Br2-Cz on top of the in-house synthesized pyrene-based SAM 4PAPyr. These findings highlight the potential of targeted molecular engineering of interlayers to optimize solar cell performance.