Introducing thiophene and benzothiadiazole groups in triphenylamine-based organic dyes with rigidly fused π-bridge to design high-efficiency solar cells: A theoretical investigation

Abstract The influence of different types of π-bridges in triphenylamine-based organic sensitizers on their photophysical and photovoltaic properties is investigated by using sophisticated first-principles calculations and reliable theoretical models. Two well-designed strategies, namely the cyclization between separate benzothiadiazole and bithiophene as well as the insertion of electron-rich/deficient groups between the rigidly fused π-bridge and anchor moieties are proposed. It is found that the calculated photophysical and photovoltaic parameters of the dye with an unfused π-bridge reproduce very well the available experimental data, ensuring the rationality of present theoretical methods and models. The designed dye featuring a rigidly fused π-bridge shows a remarkable decrease of power conversion efficiency (PCE), with respect to the dye with an unfused π-spacer (6.36% vs. 11.18%), which implies that simply cyclizing separate aromatic heterocyclic groups is unfavorable for improving the photoelectrical performance. However, the PCE can be increased to 14.20% when an electron-rich thiophene group is introduced between the fused π-bridge and the anchor units. More importantly, replacing the thiophene moiety with an electron-deficient benzothiadiazole group can further improve the photovoltaic performance, and consequently a PCE as high as 23.81% is achieved, which is a significant theoretical improvement for triphenylamine-based organic dyes. To sum up, this study theoretically elucidates the effect of unfused and fused π-bridges as well as the introduction of electron-rich/deficient groups in organic dyes on their photophysical and photoelectric properties and provides a useful guidance for further designing highly-efficient dye sensitizers by molecular engineering.