Rational Design Of 2d P-Pi Conjugated Polysquaraines For Both Fullerene And Nonfullerene Polymer Solar Cells

So far, squaraine-based polymer donors have been less explored for the bulk heterojunction (BHJ) polymer solar cells. In this work, two new p-pi conjugated polysquaraines (PASQ-BDT1 and PASQ-BDT2) with different electron-rich subunits on the squaraine skeleton are rationally developed as new polymer donors based on the 2D structure design concept. PASQ-BDT2 with N,N-diisobutylaniline subunits shows superior device performances in both fullerene and nonfullerene PSCs compared to PASQ-BDT1 containing triphenylamine subunits, with power conversion efficiencies (PCEs) of 4.34% and 3.72%, respectively, owing to increased light-harvesting ability and more favorable nanoscale morphology in the BHJ films. Moreover, its demonstrated that solvent effects can play an effective role in elevating the device performance. For the PASQ-BDT2/PC71BM blend, the PCE is improved from 3.19% to 4.34% after solvent vapor annealing treatment, mainly attributed to the optimized film morphology and increased hole mobility. More interestingly, when the processing solvent for nonfullerene devices is changed from chlorobenzene to chloroform, a significant enhancement on PCE from 1.96% to 3.72% is yielded for the PASQ-BDT2/ITIC blend, due to suppressed charge recombination and enhanced crystallinity in the chloroform-processed BHJ films.