Recent Advances of Dopant-Free Polymer Hole-Transporting Materials for Perovskite Solar Cells

Perovskite solar cells (PVSCs) have achieved incredible progress in power conversion efficiency (PCE) from 3.8% to 25.2% in the past decade. With the requirement of commercial applications, the stability of PVSCs is gradually arousing widespread concern and has become a key problem that must be solved. As an important part of PVSCs, hole-transporting materials (HTMs) play an important role in affecting the overall device performance. However, for many reported HTMs, the chemical doping process is generally required to improve the hole mobility/conductivity, which not only increases the overall cost of device but also damages the long-term device stabilities. Although the development of HTM-free PVSCs is a feasible solution to address the stability issue caused by doped HTMs, it unfortunately will sacrifice the device efficiency. As a result, significant efforts have been devoted to developing dopant-free HTMs. Dopant-free polymer HTMs have advantages such as high heat resistance, high hydrophobicity, and excellent film-processing ability for large-scale production and have shown very good device efficiency and stability in different types of device structures. Herein, a review is presented on the recent advances of dopant-free polymer HTMs for PVSCs, outlining their development with reasonable molecular design strategies toward promising material properties and device performance. Finally, an outlook and some advice regarding the future design of dopant-free polymer HTMs are proposed on the basis of the summary of development status and the study of the structure–property–performance relationship.