Same Benzodithiophene Unit-Based Polymer Acceptor and Donor with High Molecular Compatibility Enabled Efficient, Thermally Stable, and Mechanically Robust All-Polymer Solar Cells

The existing class of polymer solar cells is undergoing a dilemma between two types of acceptors; i) non-fullerene small molecular acceptors (NFSMAs) with high power conversion efficiencies (PCEs) but inferior operational stabilities, and ii) polymer acceptors (P_As) for all polymer solar cells (all-PSCs) with excellent stabilities but lower PCEs due to demixing of polymer donors (P_Ds) and polymer acceptors (P_As). Here, we design new P_As [P(BDT2BOY5-X), X = H, F, Cl], based on two major principles; i) polymerizing NFSMA to endow both excellent efficiency and mechanical ductility, and ii) embedding same building unit (i. e., BDT) into both the P_D and P_A to generate high molecular compatibility. The all-PSCs with P(BDT2BOY5-X) P_As exhibit highly enhanced morphological compatibilities, higher PCE (11.12%) and superior thermal/mechanical stabilities compared to the devices with NFSMA or conventional P_A, suggesting a crucial consideration in the P_A designs for efficient and stable all-PSCs.