The evaluation of structure and optical properties of CH3NH3[LaxPb1-x]I3; (0 ≤ x ≤ 0.07) trihalide perovskite films prepared by solution growth approach

Highly crystalline CH3NH3[LaxPb1-x]I3 (0 ≤ x ≤ 0.07) films are developed on quartz substrates using solution growth approach. The influence of lanthanum ions on the structural, morphological and optical properties of the La-doped methylammonium lead iodide perovskite films were examined by the X-ray diffraction, scanning electron microscope, Raman spectroscopy and UV-vis spectrophotometery. The films exhibited polycrystalline orthorhombic perovskite crystal structure, suggesting the solubility of the La ions in the CH3NH3PbI3 perovskite crystals. The orthorhombic distortion factor disclosed the incorporation of 3 mol% of La ions in the CH3NH3PbI3 perovskite crystal promote the symmetry of these crystal. The Raman spectra revealed three transverse optical phonon modes and three longitudinal optical phonons modes. The decrease of the ratio of the 96/110 bands and the peak position shift towards low frequency, implying the decrease of the concentrations of the PbI2 into the orthorhombic perovskite crystal and these films become more polarizable. Among all films, the CH3NH3[La0.03Pb0.07]I3 film has shown high optical absorption, low transmittance and very low reflectance. The increase of the amount of La ions from 0 to 3 mol% resulted in a decrease of the band gap from 1.51 eV to 1.44 eV, then an increase to 1.47 eV when the concentration reached to 7 mol%. The CH3NH3[La0.03Pb0.07]I3 film showed very low dissipation factor and high optical conductivity, implying the opportunity to use this composition for the development of photovoltaics and photodiodes applications.