Exploration of the Effect of Fluoridation on the Doping-Free Linear Dibenzothiophene-Based Hole-Transport Material Applied for Inverted Perovskite Solar Cells

Abstract

The utilization of hole-transport materials (HTMs) in perovskite solar cells (pero-SCs) is essential for the betterment of hole extraction and hole transport, both of which are critical for enhancing efficiency. To commercialize pero-SCs, the improvement in highly efficient and cost-effective HTMs without dopants is essential. As the HTMs used in inverted pero-SCs, two dibenzothiophene (DBT)-based small linear compounds, denoted DBT-MOP (with the methoxyphenyl in the peripheral) and DBT-2F-MOP (with fluorinated methoxyphenyl in one branch), are designed and synthesized in this study. Compared to fluorinated DBT-2F-MOP, DBT-MOP shows an amorphous state, increasing hole-transport mobility, and greater charge extraction; thus, the inverted device based on DBT-MOP exhibits a remarkable efficiency of 19.5%, while the devices based on DBT-2F-MOP show an efficiency only reaching up to 15.19%. The efficiency of the DBT-MOP-based devices is among the top efficiencies of the DBT-based HTMs. However, the introduction of the fluoride atom near the methoxy group harms the enhanced efficiency, which may originate from the crystallization of DBT-2F-MOP, leading to a rugged film morphology of DBT-2F-MOP, thus further affecting the crystallization of the on-top perovskite layer.