Rational design of phenothiazine-based hole transport material with fluorene-containing asymmetric peripheral donor group for perovskite solar cells

Developing low-cost and highly efficient hole transport materials (HTMs) is extremely important to promote the industrial application of perovskite solar cells (PSCs). Phenothiazine (PTZ) is validated as promising building block to construct low-cost and highly efficient HTM for PSCs. In this work, by using PTZ as core unit, we reported two HTMs, termed PTZT-MPF and PTZT-FF, through substituting the peripheral methoxybenzene group with fluorene. The asymmetric fluorene substituted donor provides the corresponding HTM PTZT-MPF with higher hole mobility, suitable frontier molecular orbital energy levels and smoother film morphology. As a result, the PTZT-MPF based PSCs exhibits a promising PCE of 20.15% with an enhanced open-circuit (Voc) of 1.13 V, even higher than well-known Spiro-OMeTAD. Meanwhile, with the fluorene substitution, the hydrophobicity of HTM is promoted with improved, and guarantee improved long-term stability for PTZT-MPF based PSCs.