Bending the Rule: Naphthobisthiadiazole-Based Terpolymers with Both High Solubility and Crystallinity for Organic Photovoltaics

Achieving a good balance between the crystallinity and solubility is of great importance in the design of π-conjugated polymers. Here, we synthesized a series of terpolymers in which small fractions of a planar V-shaped fused ring, triphenyleno­[1,2-c:7,8-c′]­bis­([1,2,5]­thiadiazole) (TPTz), are incorporated into the linear-shaped backbone of a highly crystalline polymer based on naphtho­[1,2-c:5,6-c′]­bis­([1,2,5]­thiadiazole) (NTz), PNTz4T. Due to the “bending” structure induced by the TPTz unit, the terpolymers had greatly improved solubility by about 5–9 times compared to the linear-shaped PNTz4T. In particular, the terpolymers preserved the crystallinity of PNTz4T to a considerable extent with a higher fraction of face-on oriented domains in films. As a result, the highly solution-processable terpolymers exhibited high photovoltaic performances and slightly outperformed PNTz4T. Our results indicate that the incorporation of a V-shaped unit into a linearly shaped polymer is a good strategy to develop π-conjugated polymers with high solubility and crystallinity.