Side-Chain Engineering on Dopant-Free Hole-Transporting Polymers toward Highly Efficient Perovskite Solar Cells (20.19%)

A variety of dopant-free hole-transporting materials (HTMs) is developed to serve as alternatives to the typical dopant-treated ones; however, their photovoltaic performance still falls far behind. In this work, the side chain of a polymeric HTM is engineered by partially introducing diethylene glycol (DEG) groups in order to simultaneously optimize the properties of both the bulk of the HTM layer and the HTM/perovskite interface. The intermolecular pi-pi stacking interaction in the HTM layer is unexpectedly weakened after the incorporation of DEG groups, whereas the lamellar packing interaction is strengthened. A doubled hole mobility is obtained when 3% of the DEG groups replace the original alkyl side chains, and a champion power conversion efficiency (PCE) of 20.19% (certified: 20.10%) is then achieved, which is the first report of values over 20% for dopant-free organic HTMs. The device maintains 92.25% of its initial PCE after storing at ambient atmosphere for 30 d, which should be due to the enhanced hydrophobicity of the HTM film.