Semi-Locked Tetrathienylethene as Promising Building Block for Hole Transporting Materials: Toward Efficient and Stable Perovskite Solar Cells.

The construction of state-of-the-art hole transporting materials (HTMs) always meets a dilemma in modulating the molecular configuration for simultaneously achieving high morphology uniformity and charge mobility, especially in due to the lack of appropriate building blocks. Herein a semi-locked tetrathienylethene (TTE) as promising building block is reported for HTMs via fine tuning molecular planarity. Upon incorporation of four triphenylamine groups in the resulting TTE-2, we have for the first time realized a specific hybridization of orthogonal and planar conformation, thus leading to the desirable electronic and morphological properties in perovskite solar cells (PSCs). Owing to its high hole mobility, deep lying HOMO level and excellent thin film quality, the dopant-free TTE-2 based PSCs exhibit a very promising efficiency over 20% with long-term stability, achieving the best performances among dopant-free HTM based planar n-i-p structured PSCs.