Optoelectronic analysis of 4,4′-(3,4-dimethoxythiophene-2,5-diyl)bis(N,Ndiphenylaniline) based donor- π -acceptor chromophores for photovoltaic applications towards organic and perovskite solar cells

Abstract Hole transport materials (HTMs) play a vital role in perovskite solar cells (PSCs) by facilitating hole transport and exciton dissociation. Developing efficient HTMs is therefore key to improving device stability and photoelectric conversion efficiency. In this work, we designed a series of high-twist thiophene-based HTMs with donor-pi-acceptor (D- π -A) structures through end-capped acceptor engineering. The optoelectronic properties of the parent molecule (D1) and five newly designed (D1-A1 to D1-A5) derivatives were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT). Compared with reference materials, the engineered HTMs exhibited enhanced hole mobility, stronger intramolecular charge transfer, and maximum absorption in the 562–740 nm range. TD-DFT reveals a bimodal absorption response: 562–606 nm (D1-A2/A4/A5) versus 730–740 nm (D1-A1/A3), attributed to stronger acceptor end-groups that deepen the LUMO, narrow the HOMO–LUMO energy gap, and intensify ICT. They also demonstrated excellent photostability under continuous illumination. Energy-level alignment between the HOMO/LUMO of the HTMs and the perovskite layer facilitated efficient charge transfer while minimizing energy losses. Moreover, the HTMs showed lower hole reorganization energies (0.177 to 0.221 eV) than electron reorganization energies (0.210 to 0.871 eV), higher transfer integrals (0.19–0.26 eV), and faster hole hopping rates (1.63 × 10 9 to 1.41 × 10 11 ), confirming their suitability for efficient charge transport with reduced recombination losses. These synergistic properties make the designed HTMs promising candidates for enhancing PSC efficiency and long-term stability. This study demonstrates that precise acceptor engineering is a powerful strategy for developing next-generation HTMs with superior photovoltaic performance.