Molecular Tailoring of Phenothiazine-Based Hole-Transporting Materials for High-Performing Perovskite Solar Cells

Phenothiazine-based compounds, PTZ1 and PTZ2, were synthesized through straightforward Buchwald–Hartwig and Suzuki–Miyaura cross-couplings, respectively, by binding the suitable donor groups (diarylamine or triarylamine) to a phenothiazine core. Phenothiazine-based structures were proven for the first time as hole-transporting materials in solution-processed lead trihalide perovskite-based solar cells. A dramatic effect exerted by the presence of phenylene spacers was observed on the relevant photovoltaic performances. The power conversion efficiencies measured under AM1.5 sun increase from 2.1% (PTZ1) to a remarkable 17.6% (PTZ2), a value rivaling those obtained with the state-of-the-art Spiro-OMeTAD (17.7%). These results indicate phenothiazine-based compounds as promising candidates to be used as readily available and cost-effective hole-transporting materials in perovskite solar cells.