D–A–D- and A–A–D-Type Cyanopyridone Derivatives as a New Class of Hole-Transporting Materials for Perovskite Solar Cells

The present study focused on the development and characterization of four new low-cost hole-transporting materials (HTMs), ZZ01, DJ01, PR01, and PM01, designed based on the concepts of donor–acceptor–donor (D–A–D) or acceptor–acceptor–donor (A–A–D) for application in perovskite solar cells (PSCs). These molecules were systematically synthesized and extensively analyzed for their structural, photophysical, electrochemical, thermal, density functional theory (DFT), and charge transport properties. The absorption and emission spectra of the synthesized molecules exhibited bands in the ranges of 380–393 and 457–495 nm, respectively, and demonstrated appropriate energy levels, with a band gap ranging from 2.78 to 2.91 eV, which matches well with the requirements for PSCs. The thermogravimetric analysis confirmed their thermal stability up to 230–418 °C, which is crucial for device durability. Theoretical calculations via DFT and TD-DFT corroborated the experimental findings, validating that the HOMO–LUMO energy levels and reorganization energies were conducive to effective hole transport. Xerographic time-of-flight measurements indicated superior hole mobility of 2 × 10^–5 cm²/V·s for ZZ01, highlighting its potential as an efficient HTM. Overall, this research underscores the promising candidacy of synthesized π-conjugated molecules as HTMs in PSCs, offering a pathway toward enhancing device performance and commercial viability in the field of renewable energy.