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

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.