Insight Into Designing High‐Performance Polythiophenes for Reduced Urbach Energy and Nonradiative Recombination in Organic Solar Cells

Abstract In the pursuit of high‐efficiency polythiophene (PT) organic solar cells (OSCs), a critical challenge is the reduction of nonradiative recombination. This study comprehensively explores polydithienylthiazolothiazole (PTTz)‐based PT terpolymers: PTTz‐Tz and PTTz‐TzT, in which it is demonstrate that molecular structure alterations greatly influence the aggregation kinetics and orientation of these polymers. Specifically, PTTz‐TzT achieves rapid ordering aggregation during spin coating, effectively suppressing excessive polymer aggregation and facilitating appropriate phase separation upon mixing with the acceptor. Meanwhile, PTTz‐TzT inherently adopts a face‐on orientation, resulting in more structured π–π stacking in the vertical direction after acceptor integration, compared to the intrinsic edge‐on orientation of PTTz‐Tz. These factors collectively contribute to lower Urbach energy and a substantial reduction of nonradiative recombination in PTTz‐TzT‐based OSCs, culminating in a high photovoltaic conversion efficiency (PCE) exceeding 16%. Furthermore, a prominent PCE of 19.11% is obtained by PTTz‐TzT via ternary blend strategy, which is among the highest values reported for the OSCs. This investigation underscores the significance of aggregation kinetics and orientation in PT‐based polymers, especially regarding Urbach energy and nonradiative recombination, and offers novel insights for designing high‐performance polythiophene donors.