Effectively enhancing the open-circuit voltage via chlorinated substitution in DPP-based polymer donor for polymer solar cells

[Display omitted] •Enhanced open-circuit voltage from 0.74 to 0.86 V was achieved.•Cl-substituted PDPP-BDT-Cl exhibited deeper HOMO by 0.18 eV than PDPP-BDT.•PDPP-BDT-Cl showed better thickness tolerance for more stable PCE. Herein, via chlorinated substitution in thiophene side-chain of benzo[1,2-b:4,5-b']dithiophene (BDT) unit, the diketopyrrolopyrrole (DPP) containing conjugated polymer PDPP-BDT-Cl is designed, which exhibits fine-tuned HOMO energy level with 0.18 eV deeper than the control PDPP-BDT without chlorination. When applied as donor material with 6,6-phenyl-C71-butyric acid methyl ester (PC71BM) acceptor in bulk heterojunction polymer solar cells(PSCs), enhanced open-circuit voltage (VOC) to 0.86 V and average power conversion efficiency (PCE) to 5.02% could be achieved for PDPP-BDT-Cl based PSCs compared to 0.74 V and 4.53% for PDPP-BDT. Furthermore, PDPP-BDT-Cl polymer demonstrate better thickness tolerance for more stable photovoltaic performances due to better donor/acceptor miscibility.