Leverage of Pyridine Isomer on Phenothiazine Core: Organic Semiconductors as Selective Layers in Perovskite Solar Cells.

To drive the development of perovskite solar cells (PSCs), hole-transporting materials are imperative. In this context, pyridine derivatives are being probed as small molecules-based hole-transporting materials due to their Lewis base and electron-deficient unit. Herein, we focused our investigation on pyridine isomer molecules 4,4'-(10-(pyridin--yl)-10-phenothiazine-3,7-diyl)bis(,-bis(4-methoxyphenyl)aniline) ( = , , or ), in which the pyridine nitrogen heteroatom is located at the 2, 3, and 4 positions, named as , , and , respectively. We decipher the structure-properties-device performance relationship impacted by the different -atom positions in pyridine. In the case of , the partial orbital overlap between highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) favors the generation of neutral excitons and hole transport, as well as improves the film-formation ability, and this induces efficient hole extraction as compared to their 2,4 analogues. The solar cells fabricated with gave on-par photovoltaic performance as that of typical Spiro-OMeTAD, and higher performance than those of and . The hydrophobicity and homogeneous film properties of add merits to the stability. This work emphasizes the guidelines to develop small molecules for organic solar cells, organic light-emitting diodes, and thermally activated delayed fluorescence.