Non-halogenated solvent processable wide bandgap polymer based on carboxylate-substituted benzodithiophene for high-efficiency polymer solar cells

The use of non-halogenated solvents for the fabrication of polymer solar cells (PSCs) is a crucial step for commercial applications in the future. Herein, we synthesize a wide bandgap polymer PBDT-ST with alkylthio chains substituted benzodithiophene (BDT) as donor unit and carboxylate-substituted BDT as acceptor unit. The polymer PBDT-ST possesses a wide bandgap over 1.90 eV and a deep highest occupied molecular orbitals (HOMO) levels below −5.50 eV, which is beneficial to obtain a high open circuit voltage (Voc). In addition, PBDT-ST shows good solubility in halogenated and non-halogenated solvents. The o-xylene processed PBDT-ST:ITIC-2F blend film exhibits improved molecular order, film morphology and charge mobilities compared with o-dichlorobenzene (o-DCB) processed one. As the results, the o-DCB processed PBDT-ST:ITIC-2F based device can achieve a power conversion efficiency (PCE) of 10.48%. When the non-halogenated o-xylene as solvents and non-halogenated diphenyl ether (DPE) as additive, an improved PCE of 11.14% can be obtained with Voc of 0.90 V, Jsc of 17.83 mA/cm2 and FF of 69.36%. Our research indicates that carboxylate-substituted BDT based polymer PBDT-ST as a promising wide bandgap donor material can achieve excellent photovoltaic performance for PSCs processed by non-halogenated solvent.