A Low-Cost and Non-Noble Metal Catalyst Synthesis of Phenothiazine-Based Polymer HTM for Efficient and Stable Perovskite Solar Cells

The creation of affordable hole-transporting materials (HTMs) is necessary for the commercialization of perovskite solar cells (PSCs). Herein, a low-cost phenothiazine (PTZ)-based HTM (PPTZ) was designed and synthesized. Notably, PPTZ was synthesized with simple procedures, avoiding the use of noble metal catalysts and butyllithium, which considerably reduces the cost of the synthesis and the hazards of the operation. Compared with the traditional polymer HTMs (PTAAs), PPTZ has lower synthesis cost ($35.22 g–1), which brings significant potential for commercial application. Besides, it exhibits a deeper HOMO energy level at around −5.57 eV due to the excellent electron-giving properties, which reduces the energy level gap with perovskite and the voltage losses. It greatly improves the fill factor (FF) and the open-circuit voltage (VOC) of the corresponding device. As a result, it demonstrates a higher power conversion efficiency (PCE) of 21.38% compared with PTAA (19.8%), along with excellent stability. The device based on PPTZ maintained 80% of its original efficiency in nitrogen for over 800 h under maximum-power point tracking.