Significant Influences of Elaborately Modulating Electron Donors on Light Absorption and Multichannel Charge-Transfer Dynamics for 4-(Benzo[c][1,2,5]thiadiazol-4-ylethynyl)benzoic Acid Dyes

4-(Benzo[c][1,2,5]thiadiazol-4-ylethynyl)benzoic acid (BTEBA) as a promising electron acceptor has been used in the highly efficient organic dye-sensitized solar cells (DSCs) recently. Because of its strong electron-deficient character, BTEBA could bring forth a remarkable decline in the energy level of the lowest unoccupied molecular orbital (LUMO) and further reduce the energy gap of dye molecules significantly. In this contribution, two metal-free organic dyes WEF1 and WEF2 were synthesized by simply combining BTEBA with two slightly tailored electron-releasing moieties: 4-hexylphenyl substituted indaceno[1,2-b:5,6-b']dithiophene (IDT) and cyclopenta[1,2-b:5,4-b']dithiophene[2',1':4,5]thieno[2,3-d]thiophene (CPDTDT), which were screened rationally from an electron-donor pool via computational simulation. With respect to those of WEF1, WEF2-sensitized solar cells demonstrate a far better short-circuit photocurrent density (JSC) and open-circuit photovoltage (VOC), resulting in a ∼50% improved power conversion efficiency of 10.0% under irradiance of 100 mW cm(-2) AM1.5G sunlight. We resorted to theoretical calculations, electrical measurements, steady-state, and time-resolved spectroscopic methods to shed light on the fatal influences of elaborately modulating electron donors on light absorption, interfacial energetics, and multichannel charge-transfer dynamics.