Design, Synthesis, and Postvapor Treatment of Neutral Fulleropyrrolidine Electron-Collecting Interlayers for High-Efficiency Inverted Polymer Solar Cells

A novel fullerene derivative (FBPNOH) grafted with bilateral polar pendants was explored as an efficient electron-collecting layer (ECL) for inverted polymer solar cells (i-PSCs). Using PTB7-Th:PC71BM as the photoactive material, the devices based on FBPNOH achieved power conversion efficiencies (PCEs) exceeding 8.85%, which are higher than those of the reference devices based on sol-gel ZnO. The impact of postsolvent treatment on the interfacial properties and charge transport ability of interlayers and the corresponding optoelectronic characteristics have been systematically investigated in comparison with those of its unilateral counterpart (FPNOH). The results show that the post-solvent annealing process is beneficial for enhancing the carrier transport and extraction characteristics of fullerene-based ECLs for PSCs. Meanwhile, according to ultraviolet photoelectron spectroscopy, dimethyl-formamide solvent annealing can further reduce the work function of indium tin oxide. The electron-selective device tests confirmed the improvement in the charge transport ability for the solvent-annealed films, which boosted PCEs to 9.49% and 10.05% for the typical i-PSCs based on FBPNOH and FPNOH as the ECL, respectively. Our findings shed light on further optimizing the molecular design and device engineering of ECLs for photovoltaic applications.