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‐(2ʹ,4ʹ‐bis(hexyloxy)‐[1,1ʹ‐biphenyl]‐4‐yl)‐2ʹ,4ʹ‐bis(hexyloxy)‐N‐methyl‐[1,1ʹ‐biphenyl]‐4‐amine and N‐(2ʹ,4ʹ‐bis(dodecyloxy)‐[1,1ʹ‐biphenyl]‐4‐yl)‐2ʹ,4ʹ‐bis(dodecyloxy)‐N‐methyl‐[1,1ʹ‐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.