A series of two-dimensional(2D)conjugated copolymers with spatial D-A-D structures(PTNBTB,PTCBTB,and PTSBTB)consisting of hetero-atom-bridged dithiophene and phenylvinyl-substituted benzothiadiazole blocks in the main chain have been designed,synthesized,and characterized.The structure-property relationships of the resulting copolymers were systematically investigated.The effects of the bridging atoms(N,C,and Si)on their thermal,optical,electrochemical and chargetransporting properties were also studied.PTNBTB exhibits a smaller band gap with red-shifted absorption,whereas PTSBTB possesses deeper HOMO level and higher hole mobility than PTCBTB or PTSBTB.Bulk heterojunction(BHJ)solar cells were fabricated and characterized with the conventional configuration of ITO/PEDOT:PSS/copolymer:PC71BM(1:1)/Ca/Al.As expected,PTSBTB devices showed the highest PCE,up to 4.01%,which was due to the lower HOMO level,higher carrier mobility,and stronger optical response as well as the finer nanoscale phase separation of the pristine polymer and/or the corresponding blending active layer with PC71BM.The primary results offer useful insights in designing 2D copolymers with spatial D-A-D backbone and different hetero-atom bridged donor units to finely tune the absorptions,electronic energy levels,carrier mobilities and the photovoltaic properties.
