Phenothiazine-based hole transporting materials (HTMs) for inverted perovskite solar cells (IPSCs)

Inverted perovskite solar cells (IPSCs) have different advantages for future commercialization compared to the regular PSC, expecially due to their long stability. In the PSC architecture, Hole-Transporting Materials (HTMs) play a critical role to capture holes formed after the light absorption in the perovskite layer and transport them to the cathode. Spiro-OMeTAD, is the best performing organic molecule to date, however rationally designed HTMs might be crucial to improve performances of (IPSCs). We decided to synthetize two new HTMs which were based on a double phenothiazine scaffold, having triphenylamine (TPA) groups as substituents, and with a different central core: a phenyl (HTM1) and dibenzofuran group (HTM2) (figure 1). The synthesis took advantage of Pd-catatyzed Suzuki and Buchwald-Hartwig coupling reactions to assemble different molecular fragments. Optimization of the reaction conditions gave the desired molecules in good yields. The corresponding devices showed optimal results regarding both efficiency and long stability, proving HTM1 and HTM2 to be excellent candidates as hole carrier in inverted PCS.