External electric field modulation of a high-performance D–A–π–A sensitizer for dye-sensitized solar cells: a DFT/TD-DFT investigation

Abstract Rational design of metal-free organic sensitizers is crucial for advancing dye-sensitized solar cells. While D–A–π–A dyes such as XY1 show high performance, their behaviour is strongly influenced by interfacial electric fields (EFs). Using DFT/TD-DFT (CAM-B3LYP/6-311+G(d,p)) in a solvent model, we reveal a non-monotonic response of the electronic properties of XY1 to external EFs. The HOMO energy reaches a minimum at –4 × 10−4 a.u., maximizing the HOMO–LUMO gap and inducing a blueshift