Modification on C217 by auxiliary acceptor toward efficient sensitiser for dye-sensitised solar cells: a theoretical study

In this work, to develop efficient organic dye sensitisers, a series of novel donor–acceptor–π–acceptor metal-free dyes were designed based on the C217 dye by means of modifying different auxiliary acceptors, and their photovoltaic performances were theoretically investigated with systematic density functional theory calculations coupled with the incoherent charge-hopping model. Results showed that the designed dyes possess lower highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels as well as narrower HOMO–LUMO gaps compared to C217, which indicate their higher light-harvesting efficiency. In addition, using the (TiO₂)₃₈ cluster and bidentate bridging model, we predicted that the photoelectric conversion efficiency (PCE) for the C217 dye is as high as 9.92% under air mass (AM) 1.5 illumination (100 mW·cm^?2), which is in good agreement with its experimental value (9.60%–9.90%). More interestingly, the cell sensitised by the dye 7 designed in this work exhibits a middle-sized open-circuit voltage of 0.737 V, large short-circuit photocurrent density of 21.16 mA?cm^?2 and a fill factor of 0.801, corresponding to a quite high PCE of 12.49%, denoting the dye 7 is a more promising sensitiser candidate than the C217, and is worth further experimental study.