Fused perylene diimide-based polymeric acceptors for all-polymer solar cells with high open-circuit voltage

Abstract

The incorporation of fused perylene diimides (PDIs) as an acceptor (A) block into the polymer backbone was proved to be effective in reducing the aggregation of molecules to form better size domains. However, photovoltaic devices based on these polymers have a low open-circuit voltage (V_OC), which greatly limits their ability to achieve higher performance. Herein, a fused PDI dimer (TBDPDI) was used for constructing two acceptor polymers, P(TBDPDI-TT) and P(TBDPDI-FTT). Polymer P(TBDPDI-TT) was expected to be a good electron acceptor for its strong absorption at 350–700 nm, maximum extinction coefficient of up to 7.06 × 10⁴ M⁻¹ cm⁻¹, and high lowest unoccupied molecular orbital (LUMO) energy levels (−3.81 eV). When blended with PTB7-Th, all-polymer solar cells (all-PSCs) based on P(TBDPDI-TT) showed a high V_OC of 0.936 V, which was one of the highest values in the family of PDIs. A series of studies, including device optimization, dependence on light intensity, exciton dissociation, carrier mobility, and atomic force microscopy (AFM), were carried out to distinguish between the P(TBDPDI-TT)- and P(TBDPDI-FTT)-based all-PSCs. The results suggested that the PTB7-Th:P(TBDPDI-TT) device possessed better charge transport, higher and more balanced carrier mobility, less exciton recombination loss, and more favorable film morphology. Therefore, the PTB7-Th:P(TBDPDI-TT) device had a higher power conversion efficiency (PCE) compared to the PTB7-Th:P(TBDPDI-FTT) device. These results suggested that the use of TBDPDI as an A block was an effective strategy to construct polymers with high LUMO energy levels.