Mapping Nonfullerene Acceptors with a Novel Wide Bandgap Polymer for High Performance Polymer Solar Cells

A new weak electron-deficient building block, bis(2-ethylhexyl) 2,5-bis(5-bromothiophen-2-yl) thieno[3,2-b]thiophene-3,6-dicarboxylate (TT-Th), is incorporated to construct a wide-bandgap (1.88 eV) polymer PBDT-TT for nonfullerene polymer solar cells (NF-PSCs). PBDT-TT possesses suitable energy levels and complementary absorption when blended with both ITIC analogues (ITIC and IT-M) and a near-infrared (NIR) acceptor (6TIC). Moreover, PBDT-TT exhibits good conjugated planarity and preferable face-on orientation in the blended thin film, which are beneficial for charge transfer and carrier transport. The PSCs based on PBDT-TT:IT-M and PBDT-TT:6TIC blend films yield high power conversion efficiencies of 11.38% and 11.03%, respectively. To the best of the authors' knowledge, the PCE of 11.03% for PBDT-TT:6TIC-based device is one of the highest values reported for NIR NF-PSCs. This work demonstrates that TT-Th is a useful new electron-accepting building block for making p-type wide bandgap polymers for efficient NIR NF-PSCs.