Computational analysis of charge transfer and optoelectronic properties in triphenylamine-based molecules for high-efficiency organic solar cells

Abstract

• Four new d -A-A donor materials based on triphenylamine were theoretically designed. • All dyes exhibit low energy gaps and broad absorption in the visible range. • Modifications to the first acceptor unit significantly enhanced charge transfer, as evidenced by excited-state analysis. • MD simulations, including RDF and MSD analyses, demonstrated that M1 and M2 maintain an optimal balance between interaction strength and mobility. • Theoretical and computational findings suggest that M1 and M2 are the most promising candidates for organic photovoltaics, with optimized charge transfer properties and structural stability. The global energy landscape is undergoing a profound transformation, driven by the urgent need to address environmental concerns and energy security. In recent years, alternative solar energy technologies have attracted increasing interest and investment, and organic solar cells (OSCs) have emerged as promising alternatives to traditional silicon-based solar cells. In this study, a series of four M i donor materials ( i = 1–4) incorporating triphenylamine with donor-acceptor-acceptor (D-A-A) configurations was developed. These materials were designed by modifying the acceptor portion of the reference molecule TPA-R by incorporating four different fragments containing sulfur heterocycles, selenophene, and thiadiazole. The electronic and optical properties of small electron donor materials (SEDMs) were explored through theoretical analysis using density functional theory (DFT) simulations at the B3LYP/def2-SVP level of theory to optimize the geometrical structures and the TD-CAM-B3LYP/6–31G(d,p) approach to predict the excitation behavior. The theoretical results were then compared with experimental data, revealing a high degree of agreement. All the designed compounds, M1–M4, showed prominent and broad absorption peaks in the visible spectra, ranging from 595 to 726 nm, with comparatively smaller energy gaps ( E g ) than the reference TPA-R. Excited-state analysis revealed that all the designed molecules exhibited a significantly high electron-hole transfer rate from the D moiety to the second A2 acceptor, indicating that modification of the first acceptor improves the charge transfer properties. To fully understand how the small donor molecules interact with the C70 acceptor, molecular dynamics (MD) was performed.