Improving Active Layer Morphology of All-Polymer Solar Cells by Dissolving the Two Polymers Individually

All-polymer solar cells (all-PSCs) use a blend of polymer donor and polymer acceptor as the active layer. The active layer morphology in all-PSCs cannot be effectively tuned by conventional methods. Here, we report a simple method to improve the active layer morphology of all-PSCs, i.e., dissolving polymer donor and polymer acceptor individually and then blending them immediately before spin-coating (DI method). Compared with the regular method of dissolving two polymers together (DT method), the DI method leads to enhanced polymer ordering and higher domain purity due to the partially preserved polymer aggregates from solution. With poly[4-(5-(4,8-bis(5-(dodecylthio)thiophen-2-yl)-6-methylbenzo[1,2-b:4,5-b']dithiophen-2-yl)thiophen-2-yl)-5,6-difluoro-2-(2-hexyldecyl)-7-(5-methylthiophen-2-yl)-2H-benzo[d]1,2,3-triazole] (J61) as donor and poly[5,10-bis(2-decyltetradecyl)-2-(5-(2,5-difluoro-4-(5-methylthiophen-2- yl)phenyl)thiophen-2-yl)-4,4,9,9-tetra-fluoro-7-methyl-4,5,9,10-tetrahydro-3a,5,8a,10-tetraaza-4,9-diborapyrene-3a,8a-diium-5,11-diuide] (PBN-10) as acceptor, the power conversion efficiency of all-PSC device increases from 5.36% with the DT method to 7.09% with the DI method at a high open-circuit voltage of 1.24 V. This DI method is also applicable for other polymer donor/polymer acceptor systems and is expected to promote the development of all-PSCs.