Strategic modulation of heterocyclic donors in binaphthyl acrylonitrile-based hole transport materials for perovskite solar cells: a DFT and machine learning investigation

Abstract

Hole transport materials (HTMs) play a crucial role in perovskite solar cells (PSCs) by facilitating efficient charge extraction, suppressing interfacial recombination, and enhancing device stability. Here, a series of binaphthyl acrylonitrile-based organic chromophores (BNPD1–BNPD5) with heterocyclic donor moieties at their terminals were designed through molecular engineering for utilization as HTMs. The influence of the heterocyclic donor moieties on the optoelectronic properties of binaphthyl acrylonitrile-based derivatives was investigated through DFT/TDDFT methodologies at the M06/6-311G(d,p) level. The current study used CatBoost to predict the Egap of binaphthyl acrylonitrile-based derivatives to complement the DFT/TD-DFT results. CatBoost achieved high accuracy (training R2 = 0.999 and test R2 = 0.8896) and demonstrated high predictability. SHAP enhanced the interpretability and trustworthiness of the model by providing accurate predictions and interpretable insights into the relevance of molecular descriptors. Various investigations, such as UV-visible spectroscopy, hole–electron transport, frontier molecular orbital (FMO), density of states (DOS) and transition density matrix (TDM) analyses, were conducted on the entitled chromophores. The HOMO/LUMO energy gaps of BNPD1–BNPD5 were found to be within the range of 4.050–2.683 eV, with the absorption maxima observed in the UV region (434.179–393.826 nm). According to the DOS and TDM analyses, good charge transfer occurred from the terminal donors to the central acceptor in all the derivatives. All the investigated chromophores exhibited relatively low exciton binding energies, following a decreasing trend (in eV): BNPD4 (0.648) > BNPD5 (0.621) > BNPR (0.611) > BNPD2 (0.340) > BNPD3 (0.335) > BNPD1 (0.069). A benchmark study using Spiro-OMeTAD (a reference HTM) illustrated close agreement, which also suggested that these materials can act as reasonable HTMs for perovskite solar cells.