Tuning Alkyl Chain Lengths of Oxasmaragdyrins-B(OR)2 for Optimizing Hole-Transport and Efficiency in Perovskite Solar Cells

Abstract

A major challenge toward commercialization of perovskite solar cells (PSCs) is the development of cost-effective hole-transport materials (HTMs) with good hole mobility and long-term stability. Porphyrinoids such as metal-free oxasmaragdyrins as alternative HTMs in PSCs show promising power conversion at lower costs. In this study, a difluoroboryl oxasmaragdyrin, SM09, has been modified by introducing alkoxy chains with different chain lengths (methoxy (OMe), ethoxy (OEt), butoxy (OBu), and octyloxy (OOct)) at the central core position, affecting molecular packing, varying intermolecular distances, and consequently altering the hole mobility. These modified oxasmaragdyrins were used as HTMs for the planar PSCs. The device performance was evaluated and correlated with the alkyl chain length and was rationalized by photophysical characterizations. The device efficiencies decrease with an increase in the alkyl chain length from the highest PCE of 15.47% for SM-OMe to 13.35% for SM-OOct. The best performance was obtained in SM-OMe, due to its higher hole mobility (3.75 × 10–4 cm2 V–1 s–1) and stronger p-type character. In the future, a simple tuning of alkyl chain length at central core positions of oxasmaragdyrin HTMs can be an effective strategy to enhance the power conversion efficiency (PCE) of PSCs.