Structural isomerization engineering of hole transport materials for efficient perovskite solar cells

Abstract

Organic hole transport materials (HTMs) are indispensable in the currently reported high-efficiency inverted perovskite solar cells (PSCs). The chemical structures and configurations of HTMs will determine the hole transport properties and interfacial contacts. Functional groups are usually required when designing HTMs. However, the impact of substitution positions of functional groups—particularly how structural isomerization modulates the hole transport properties—remains underexplored. Herein, two isomers BABD and TABD, with the same composition but different substitution positions, are developed as HTMs for PSCs. In BABD, the ester side chain was located on the central benzene ring, and the methoxyl groups were on thiophene, while the ester group was on thiophene and the methoxyl groups on the central benzene ring in TABD. Results reveal that the intramolecular S⋯O interactions exist in TABD, which enhance molecular planarity, promote ordered molecular stacking, and thus improve hole mobility. Meanwhile, the functional groups in TABD can also passivate the defects at the bottom interface of the perovskite and promote the growth of perovskite grains. As a result, TABD-based PSCs exhibit a high efficiency of 23.24% with excellent stability. Our work highlights the need for investigation into the relationship between the functional group position and the hole transport properties of HTMs.