Simple hole transporting material based 2,7- carbazole for perovskite solar cells: Structural, photophysical, and theoretical studies

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A simple carbazole-based hole transport material, termed HTM1, has been deposited as thin films. The samples were elaborated via a Physical Vapor Deposition to ensure the production of high-quality thin films. The study of the morphological and photophysical properties of the investigated compound was revealed through Scanning Electron Microscopy, Atomic Force Microscopy, Ultraviolet–Visible, and Photoluminescence spectroscopy. A flat surface with low roughness values was observed in the SEM and AFM images. Moreover, the obtained films revealed a higher absorption in the UV region. Optical parameters such as the energy gap (2.9 eV) and refractive index were determined using transmittance measurements. The temperature-dependent photoluminescence over a range of 77–300 K has also been investigated. It is found that, as the temperature decreases, a new emission band appears, which may be due to the formation of excimers. Added to that, theoretical investigation of the highest occupied molecular orbital, the lowest unoccupied molecular orbital, the density of states, and the optical energy gap were studied using density functional theory (DFT) with the hybrid B3LYP exchange-correlation function and the 6-311G (d,p) basis set. Absorption spectra was generated using the TD-DFT method. The absorption maximum obtained (398 nm) for HTM1 closely matched with the experimental value (393 nm). Following these characterizations, simulation studies on the photovoltaic performances of the HTM1 for perovskite solar cells have been done. This cell provided a maximum PCE of 21.31%.