Co-Sensitized Solar Cell Achieves 13.7% Efficiency with Bis-Hexylthiophene Dyes

Efficient anti-aggregation and superb light harvesting in the combination of large and narrow energy gap photosensitizers play a crucial role in suppressing interfacial charge recombination in dye-sensitized solar cells (DSCs), enabling a high open-circuit photovoltage (V_oc). Here, two organic photosensitizers, H6 and H7, featuring the bulky donor N-(2',4'-bis(hexyloxy)-[1,1'-biphenyl]-4-yl)-2',4'-bis(hexyloxy)-N-methyl-[1,1'-biphenyl]-4-amine and N-(2',4'-bis(dodecyloxy)-[1,1'-biphenyl]-4-yl)-2',4'-bis(dodecyloxy)-N-methyl-[1,1'-biphenyl]-4-amine is reported, respectively, along with bis-hexylthiophene as the π-linker and the electron acceptor 4-(benzo[c][1,2,5]thiadiazol-4-yl)benzoic acid. Although the significantly longer alkyl chains do not change the optical energy gap, for H7, it has been able to design molecular structures that exhibit longer excited-state lifetimes in both dye-grafted titania and alumina films compared to its H6 counterpart. The copper-based DSC using the longer alkyl chain-based photosensitizer H7 achieves a high V_oc of 1.22 V, comparable to the recently explored hybrid methyl ammonium lead-based perovskite semiconductors (PSK) in solar cells. The co-sensitized device combined with XY1b results in an efficient DSC with an impressive fill factor of 82.1% and an excellent power conversion efficiency (PCE) of 13.7% under simulated AM1.5 G conditions at 100 mW cm^-2. Furthermore, the best device achieves an outstanding efficiency of up to 29.7% under dim light overpassing compared to the PSK solar cells.