Thieno[3,2-b][1]benzothiophene Derivative as a New π-Bridge Unit in D-π-A Structural Organic Sensitizers with over 10.47% Efficiency for Dye-Sensitized Solar Cells

Three new thieno[3,2-b][1]benzothiophene (TBT)-based donor-π-acceptor (D-π-A) sensitizers, coded as SGT-121, SGT-129, and SGT-130, have been designed and synthesized for dye-sensitized solar cells (DSSCs), for the first time. The TBT, prepared by fusing thiophene unit with the phenyl unit of triphenylamine donor, is utilized as the π-bridge for all sensitizers with good planarity. They have been molecularly engineered to regulate the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy levels and extend absorption range as well as to control the electron-transfer process that can ensure efficient dye regeneration and prevent undesired electron recombination. The photovoltaic performance of SGT-sensitizer-based DSSCs employing Co(bpy)₃^2+/3+ (bpy = 2,2′-bipyridine) redox couple is systematically evaluated in a thorough comparison with Y123 as a reference sensitizer. Among them, SGT-130 with benzothiadiazole-phenyl (BTD-P) unit as an auxiliary acceptor exhibits the highest power-conversion efficiency (PCE) of 10.47% with J_sc = 16.77 mA cm^-2, V_oc = 851 mV, and FF = 73.34%, whose PCE is much higher than that of Y123 (9.5%). It is demonstrated that the molecular combination of each fragment in D-π-A organic sensitizers can be a pivotal factor for achieving the higher PCEs and an innovative strategy for strengthening the drawbacks of the π-bridge.