A Chlorinated pi-Conjugated Polymer Donor for Efficient Organic Solar Cells

We synthesized a chlorinated benzothiadiazole-T4 polymer donor PBT4T-Cl, in which a chlorine atom had been introduced at the 4 position in the middle thiophene unit to fine-tune the energy level of the final polymers. Compared with its non-chlorinated analog, the PBT4T-Cl-based devices exhibited clear increases in open-circuit voltage and fill factor, achieving power conversion efficiencies (PCEs) up to 11.18% with simple synthesis, which is the highest PCE of the chlorinated polymer-based fullerene polymer solar cells (PSCs) reported to date. Grazing incident wide-angle X-ray scattering, atomic force microscopy, and transmission electron microscopy measurements revealed an optimized morphology of the spin-coated PBT4T-Cl blend films, which supported that chlorine substitution could promote the performance of PSCs. More importantly, the PBT4T-Cl-based devices showed superior stability, with a PCE of 8.16% after 50 days' device storage. Through this research, the chlorination of low-bandgap polymers provides new insight into designing p-conjugated polymer semiconductors and realizing further enhancement of polymer solar cell efficiency as well as stability.