Morphology evolution via solvent optimization enables all-polymer solar cells with improved efficiency and reduced voltage loss

The progress in all-polymer solar cells (all-PSCs) is often accompanied with morphology evolution of the light-harvesting layer. However, the regulation of the bulk-heterojunction (BHJ) morphology of the active layer often encounters obstacles, mainly because of the undesired miscibility of the polymer donor and acceptor. Here, we regulated the BHJ morphology of all-PSCs based on an electron-donating PBDB-T (poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b ']dithio-phene))-alt-(5,5-(1 ',3 '-di-2-thienyl-5 ',7 '-bis(2-ethylhexyl)benzo[1 ',2 '-c:4 ',5 '-c ']dithiophene-4,8-dione)]) and an electron-accepting polymer PFA1 via selection of solvents, and found that the PBDB-T:PFA1 film processed with chlorobenzene revealed a smaller phase separation scale than the chloroform processed film, mainly because of the significantly improved miscibility in the PBDB-T:PFA1 blend. Benefitting from the optimized BHJ morphology, the PBDB-T:PFA1 device processed by chlorobenzene achieved a satisfactory power conversion efficiency (PCE) of 15%, obviously higher than that of 12.25% for the chloroform processed device. Meanwhile, the voltage loss of the chlorobenzene processed device is well suppressed comparing with the chloroform processed device, demonstrating unexpected advances of morphology evolution for all-PSCs.