Enhanced photovoltaic performances of C219-based dye sensitisers by introducing electron-withdrawing substituents: a density functional theory study

In this work, seven novel sensitisers with the donor-acceptor-π-spacer-acceptor (D-A-π-A) structure were designed based on the C219 dye by introducing different electron-withdrawing substituents, and their photovoltaic parameters were predicted by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations coupled with the Marcus charge transfer model. Results showed that the introduction of electron-withdrawing substituents can narrow the HOMO–LUMO gap, and remarkably enhance the dye's sunlight absorption. By exactly estimating the charge transfer rates and efficiency in electron injection and recombination processes, the photoelectric conversion efficiency (PCE) for the C219 dye was estimated to be about 7.4% under the standard AM 1.5G solar radiation, which is in excellent agreement with its measured value of 7.6%, suggesting that our calculation scheme is reliable. Moreover, we predicted that the PCE values for most designed dyes are over 10%, indicating that the molecular design strategy used by us in this work is reasonable. Especially, the PCE of dye 1, and 4 were predicted to be as high as 13.0% and 15.7% respectively, illuminating that the –CF3 and –CN are excellent substituents. Totally, our results revealed that the dye 1 and 4 are potential candidates as efficient sensitisers, and worth further study by experiments.