Theoretical Study of WS-9-Based Organic Sensitizers for Unusual Vis/NIR Absorption and Highly Efficient Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) are the most promising low-cost photovoltaic devices. Whereas, the absorption bands of most organic sensitizers, the most vital component in DSSCs, are limited to a relatively narrow visible range. To obtain efficient sensitizer, a series of D–A−π–A metal-free dyes have been designed based on one of the best sensitizers WS-9 by modifying auxiliary acceptor and characterized theoretically. The results illustrate that introduction of auxiliary heterocycle acceptor is revealed to very narrow band gap (HOMO–LUMO), leading to an obvious red-shifted broad near-infrared absorption band in the range of 750–1950 nm compared to WS-9 (536 nm). The critical parameters in close connection with the short-circuit current density (J_sc), open circuit voltage (V_oc), including singlet excited state lifetime (τ), total dipole moments (μ_normal), the conduction band of edge of the semiconductor substrate (ΔE_CB), and regeneration driving forces (ΔG_reg) are superior to those of WS-9. Therefore, these novel sensitizers would be a promising candidate for improving the performance of the DSSCs.