Side-chain modification of polyethylene glycol on conjugated polymers for ternary blend all-polymer solar cells with efficiency up to 9.27%

With the rapid progress achieved by all-polymer solar cells (all-PSCs), wide-bandgap copolymers have attracted intensive attention for their unique advantage of constructing complementary absorption profiles with conventional narrow-bandgap copolymers. In this work, we designed and synthesized a wide bandgap ternary copolymer PEG-2% which has the benzodithiophene-alt-difluorobenzotriazole as the backbone and the polyethylene glycol (PEG) modified side chain. The PBTA-PEG-2%:N2200 can be processed with a non-chlorinated solvent of 2-methyl-tetrahydrofuran (MeTHF) for the binary all-PSC, which exhibits a moderate photovoltaic performance. In particular, the ternary all-PSCs that consisting an additional narrow bandgap polymer donor PTB7-Th can also be processed with MeTHF, resulting in an unprecedented power conversion efficiency (PCE) of 9.27%, and a high PCE of 8.05% can be achieved with active layer thickness of 240 nm, both of which are the highest values so far reported from all-PSCs. Detailed investigations revealed that the dramatically improved device performances are attributable to the well-extended absorption band in the photoactive layer. Hence, developing novel copolymers with tailored side chains, and introducing additional polymeric components, can broaden the horizon for high-performance all-PSCs.