Performable enhancement of C220-based dyes via inserting auxiliary electron acceptors for dye-sensitized solar cells: a theoretical investigation

Motivated by the exploration for high-performable sensitizers, in this work six novel organic donor–acceptor–π–spacer–acceptor (D–A–π–A) dyes were designed by inserting auxiliary electron acceptors into the C220 dye, and their photovoltaic performances were predicted by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations coupled with the charge hopping model. Results revealed that the insertion of auxiliary electron acceptors can clearly stabilize the LUMO, narrow the HOMO–LUMO gap, and remarkably enhance the dye’s optical absorption. Based on the estimation for the rates and efficiencies in charge injection, recombination, and dye regeneration processes, the photoelectric conversion efficiency (PCE) of C220 dye was predicted to be about 10.39% under standard solar radiation, in line with its measured value of 10.1%, suggesting that our calculation scheme is reliable. With the same strategy, the predicted PCE values for the dye 2, 3, and 4, with BTD, BSD and DPP as auxiliary electron acceptors, are as high as 13.17, 14.05 and 15.70%, respectively; illuminating that these three dyes are potential sensitizers for TiO2 nanocrystalline solar cells, and worth further study by experiments.