Asymmetric 2D benzodithiophene and quinoxaline copolymer for photovoltaic applications

Two novel copolymer donors based on one-dimensional (1D)-two-dimensional (2D) asymmetrical benzodithiophene (BDT) units (BDTPH-H and BDTPH-OR) and 2,3-diphenyl-5,8-di(thiophen-2-yl) quinoxaline (DTQx) were synthesized and compared with one-dimensional or two-dimensional symmetric BDT unit based photovoltaic polymers. Both asymmetrical polymers exhibited promising photovoltaic performance compared with 1D and 2D symmetric BDT polymers. The power conversion efficiency (PCE) of PBDTPH-DTQx based polymer solar cells is 5.6%, with balanced V-OC = 0.7 V, J(SC) = 11.89 mA cm(-2) and FF = 67.3%, which is almost the highest PCE compared with similar BDT unit and fluorine-free substituted DTQx based polymer. What is more, PBDTPH-DTQx shows better performance than PBDTPHO-DTQx due to the single phenyl making DTQx more planar and with better pi-pi stacking than alkoxy phenyl. These findings demonstrate that the 1D-2D asymmetrical BDT units are also applicable to poor planarity fluorine-free substituted quinoxaline acceptor system.