Optoelectronic performance of diphenylamine-helicene derivatives as hole transport materials in perovskite solar cells: a DFT/TD-DFT study

Achieving high efficiency in perovskite solar cells depends critically on the design of small-molecule hole-transport materials (HTM), and leveraging theoretical design alongside in-depth structure–property analysis offers a cost-effective screening strategy. In this work, we employ DFT at the B3LYP/6-311G(d) and TD-DFT at CAM-B3LYP/6-311G(d) level to evaluate a series of helicene-based diphenylamine derivatives (the HEL family) as potential HTMs. Nine members with helicene-based structure, including unsubstituted structures as well as structures with substituents (F, Cl, Br, Methyl, Ketone, and Amine in the ortho position and Methyl and Amine in the meta position), show optimal HOMO/LUMO alignments for efficient hole extraction, while the others appear unsuitable. Their computed absorption peaks lie between 354.98 and 368.96 nm, making them compatible with n–i–p cell architectures. Among these, the structure that is containing amine functional group in meta position has the narrowest band gap (2.70 eV), the most red-shifted λmax (365.28 nm), and excited-state metrics (D = 0.93 Å, H = 4.66 Å, t = − 2.75 Å, Sr = 70) that signal excellent charge separation. Its transport and thermodynamic descriptors—net charge = 0.44 e⁻, hole contribution = 52.28%, Eb ≈ 0.46 eV, IPa = 5.34 eV, ΔGsol = − 0.59 eV, λhole = 0.298 eV, mobility parameter η = 2.35 eV—further underline its superior hole-generation ability, solubility, and low reorganization energy. Collectively, these characteristics identify that structure containing amine functional group in meta position can be regarded as a highly promising HTM for MAPbI₃-based n–i–p perovskite solar cells.