Insight into the Interface Adsorption and Optoelectronic Properties of Novel ppy-Derivatives as Transparent Hole-Transporting Layers for Perovskite Solar Cells

Abstract Hole transport materials (HTMs) with excellent bulk and interfacial charge transport characteristics are crucial for enhancing the performance of perovskite solar cells (PSCs). To enhance the charge transport characteristics and better performance of HTMs, in this study, six different electron-donating groups (DMC, DPA, TPA, DTA, HPX, and PDP) were introduced at the terminal of ppy molecules, and a series of HTMs (ppy-11 to ppy-16) were designed. The results show that the HOMO levels of ppy-12 and ppy-13 are higher and closest to the valence band maximum of CH3NH3PbI3, achieving optimal energy level alignment. The absorption peaks of ppy and ppy-11 to ppy-16 all lie below 400 nm, ensuring that sunlight can pass through the hole transport layer and reach the perovskite absorption layer. The introduction of strong donor groups results in distinct intramolecular charge transfer (ICT) behavior in ppy-11 to ppy-16 molecules, in sharp contrast to the localized excitation characteristics of ppy. Moreover, all of the designed molecules exhibit higher mobilities than ppy, and ppy-13 shows the strongest adsorption energy and the largest interfacial charge transfer on the perovskite surface. In summary, ppy-13 achieves an ideal balance among energy levels, transparency, mobility, and interface properties, making it a highly promising HTM for perovskite solar cells.