Regulating the Solvent Resistance of Hole Transport Layer for High-Performance Inverted Perovskite Solar Cells

The hole transport materials (HTMs) play important roles in transporting holes and regulating perovskite crystallization in inverted perovskite solar cells (PSCs). Concerning the solubility of small-molecule-type HTMs in perovskite precursor solution during fabrication, the strategies including tailoring and crosslinking have been developed. However, how these strategies will influence the solvent resistance of the resultant hole transport layers (HTLs) and the corresponding device performance have not been systematically evaluated. Herein, upon incorporating tailoring and crosslinking groups into diazafluorene backbones, AFL-COOH and AFL-ENE are designed. Compared to the control HTM (AFL-3) with poor solvent resistance and AFL-COOH, the best solvent resistance of crosslinked AFL-ENE (AFL-ENE-CL) film leads to an HTL with the highest quality covered on electrode, which thus results in the lowest trap density, best surface contact, and hole extraction for devices involving the AFL-ENE-CL type HTL and the best power conversion efficiency of 20.8% (20.0% for AFL-COOH, 18.1% for AFL-3). Furthermore, high reproducibility and stabilities also realize for the AFL-ENE-CL-based PSC.