Chlorination strategy on polymer donors toward efficient solar conversions

Bulk heterojunction (BHJ) polymer solar cells (PSCs) are promising candidates for next-generation solar cells. Benefitting from the persistent efforts in material design and synthesis, systematic device engineering and fundamental understanding of the device physics, the power conversion efficiency (PCE) of single PSC has been pushed to surpass 15%, and that of the tandem PSCs is over 17%. Recently, chlorination has drawn much interest and the chlorinated PSCs have been frequently reported in donor-acceptor (D-A) type conjugated polymers. This review summarizes the recent progress of the chlorinated strategy for highly efficient photovoltaic applications. We firstly discuss the chlorination on the acceptor units in D-A type donor polymers, emphasizing the 4 widely used acceptor units with their improved PCE. secondly, the chlorination on the donor units will be discussed, mainly focusing on the chlorination of benzo[1,2-b:4,b′]dithiophene (BDT) unit and 2,2′-bithiophene unit. Remarkably, the PCE of the chlorinated BDT-based device has been improved to over 14%. Overall, this review discusses the structure-property correlations of these chlorinated polymers in photovoltaic study, which could further provide guidance on the chlorinated strategy and the molecular design for high-performance photovoltaic devices.