Abstract
Large homogeneous and adherent coatings of phenethylammonium bismuth iodide were produced using the cost‐effective and scalable aerosol‐assisted chemical vapor deposition (AACVD) methodology. The film morphology was found to depend on the deposition conditions and substrates, resulting in different optical properties to those reported from their spin‐coated counterparts. Optoelectronic characterization revealed band bending effects occurring between the hybrid material and semiconducting substrates (TiO2 and FTO) due to heterojunction formation, and the optical bandgap of the hybrid material was calculated from UV‐visible and PL spectrometry to be 2.05 eV. Maximum values for hydrophobicity and crystallographic preferential orientation were observed for films deposited on FTO/glass substrates, closely followed by values from films deposited on TiO2/glass substrates.
Highlights
Organic-inorganic hybrid perovskites and perovskite-derived materials have shown unique photo- and electro-chemical properties, which derive from their high defect-tolerance,[1] well-balanced charge transfer,[2] high optical absorption coefficient[3] and long-range electron-hole diffusion length.[4]
Data modelled from the single crystal X-ray diffraction (SCXRD) standard of the crystals of [PEA]3[Bi2I9], using Diamond® software, was used to compare to the powder XRD (PXRD) pattern obtained from the film deposition
The PXRD pattern obtained from delamination of an annealed [PEA]3[Bi2I9] thin film agreed with data modelled from the SCXRD standard (Figure 2), proving the ability of aerosol-assisted chemical vapor deposition (AACVD) to deposit crystalline coatings of bismuth-based hybrid materials
Summary
The main reasons detected for such low device efficiency are the existence of non-radiative recombination induced by defect states in the bandgap, morphological flaws and the associated low carrier transport across interfaces caused by the fast crystallization of the [CH3NH3]3[Bi2I9] films.[32] Film morphology is directly related to the recombination rate of photogenerated charges, and high roughness, cracks and pin-holes are detrimental towards the PCE of the final solar cell assembly.[23] A substantial intrinsic difference between lead and bismuth-based hybrid materials lies within their crystal structures: while CH3NH3PbI3 has 3D structure of corner-sharing octahedra (perovskite structure, Figure 1a),[13] [CH3NH3]3[Bi2I9] exhibit a derived 0D array of disconnected face-sharing octahedra[33] (Figure 1b).
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