Improvement of photovoltaic performances by optimizing π-conjugated bridge for the C217-based dyes: A theoretical perspective

Abstract

In this work, a series of novel metal-free dyes were designed based on the C217 dye by changing the π-conjugated bridge, and then their electronic and optical properties were theoretically studied with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Moreover, the photovoltaic performances of designed dyes were quantitatively estimated by means of the (TiO2)38 cluster and bidentate bridging adsorption mode coupled with the incoherent charge hopping model. Results showed that bithiophene (BT) and biselenophene (BS), which redshift the strongest absorption peak about 19.7 nm and 42.7 nm, are superior to π-conjugated bridges than thieno[3,2-b]thiophene (TT). Furthermore, the photoelectric conversion efficiency (PCE) of C217 dye was predicted to be as high as 9.40%, which is in excellent agreement with the measured value (9.60% ∼9.80%). As expected, the cell sensitized by the designed dye 4 and 7 exhibited higher PCE of 11.50% and 12.69% than that sensitized by the C217 dye, an increase of 22.5% and 35.1%, denoting the dye 4 and 7 are more promising dye sensitizer candidates, and are worth further experimental studies. In addition, our results also revealed that it is essential to accurately estimate the electron injection rate and efficiency for designing and developing high- performable dye sensitizers.