Fully Locked Conjugated Backbones in Simple‐Structured Polymer Donors Enabling High‐Performance Organic Solar Cells

Abstract The development of wide‐bandgap polymer donors with cost‐effectiveness is pivotal for advancing the commercialization of organic solar cells (OSCs). However, these materials often suffer from conformational disorder and distortion, due to the presence of multiple rotatable σ‐bonds within their conjugated backbones. This study presents a series of simple‐structured polymer donors PBDT‐TBT‐X (X = H, F, and Cl), and systematically investigates the role of the type and strength of noncovalent conformational locks (NoCLs) in regulating backbone conformations, optoelectronic properties, pre‐aggregation behavior, and charge transport properties. Remarkably, the dual‐locking strategy involving S···O and S···Cl NoCLs achieves the most highly planar conformation with a fully locked backbone. As a result, the binary OSC device based on PBDT‐TBT‐Cl achieves a power conversion efficiency (PCE) of 16.11%, much higher than its PBDT‐TBT‐H (6.35%) and PBDT‐TBT‐F (12.69%) counterparts. Notably, when utilized as a third component, PBDT‐TBT‐Cl enables a ternary OSC device with a PCE exceeding 20%. This work establishes a clear conformation−property−performance relationship, underscoring the critical role of fully locked conformations in designing high‐performance and cost‐effective polymer donors.