Naphthalene Diimide-Based Terpolymers with Controlled Crystalline Properties for Producing High Electron Mobility and Optimal Blend Morphology in All-Polymer Solar Cells

We report a series of new n-type random copolymers (P­(NDI2OD-Se-Th x), where x = 0, 0.5, 0.7, 0.8, 0.9, 1.0) consisting of naphthalene diimide (NDI), selenophene-2,2′-thiophene (Se-Th), and seleno­[3,2-b]­thiophene (SeTh) to demonstrate their use in producing efficient all-polymer solar cells (all-PSCs) and organic field-effect transistors (OFETs). To investigate the effect of polymer crystallinity on the performance of all-PSCs and OFETs, we tuned the composition of the Se-Th and SeTh moieties in the P­(NDI2OD-Se-Th x) polymers, resulting in enhanced crystalline properties with a higher Se-Th ratio. Thus, the OFET electron mobility was increased with a higher Se-Th ratio, exhibiting the highest value of 1.38 × 10^–1 cm² V^–1 s^–1 with P­(NDI2OD-Se-Th 1.0). However, the performance of all-PSCs based on PBDB-T:P­(NDI2OD-Se-Th x) showed a nonlinear trend relative to the Se-Th ratio and the performance was optimized with P­(NDI2OD-Se-Th 0.8) exhibiting the highest power conversion efficiency of 8.30%. This is attributed to the stronger crystallization-driven phase separation in all-polymer blends for higher Se-Th ratio. At the optimal crystallinity of P­(NDI2OD-Se-Th 0.8) in all-PSCs, the degree of phase separation, domain purity, and electron mobility were optimized, resulting in enhanced charge generation and transport. Our works describe the structure–property–performance relationships to design effective n-type polymers in terms of crystalline and electrical properties suitable for both efficient OFETs and all-PSCs.