A green-solvent-processable polymer hole transport material for achieving 26.31% efficiency in inverted perovskite solar cells

Abstract

The polymer hole transport layer plays a critical role in inverted perovskite solar cells since they can determine the stability and photovoltaic performances of devices. However, conventional polymer hole transport materials, such as PTAA, require processing with hazardous solvents like chlorobenzene and toluene, which limits their scalability. To address this, the development of a polymer hole transport material compatible with safer, eco-friendly, and non-regulated alternative solvents is essential for advancing the large-scale production of perovskite solar cells. In this work, a new polymer hole transport material, PTACz-PO, was developed by copolymerizing triphenylamine units and diethyl-phosphonate-modified carbazole units. PTACz-PO exhibits excellent solubility in the low-toxicity, biodegradable solvent 2-methyltetrahydrofuran along with a deep highest occupied molecular orbital energy level, high hole mobility, superior passivation effects and improved wettability for enhanced interface contact. Importantly, 2-methyltetrahydrofuran-processed PTACz-PO films present superior uniformity compared to chlorobenzene-processed PTACz-PO and PTAA films. Consequently, the device achieved a record high power conversion efficiency of 26.31% among devices processed with non-halogen solvents, as reported in the literature, along with remarkable stability, retaining 95% of their initial PCE under ISOS-D-3 protocols for over 2000 h. These findings highlight PTACz-PO as a highly promising polymer hole transport material for the future commercial production of efficient and stable perovskite solar cells.