Exploring the effect of Ga3+ doping on structural, electronic and optical properties of CH3NH3PbCl3 perovskites: an experimental study

Pure and gallium (Ga)-doped CH3NH3PbCl3 perovskites are systematically prepared via a simple solution-processed technique. The as-synthesized perovskites are then analysed for their structural, optical, morphological, elemental and electronic properties using X-ray powder diffraction (XRD), UV–Vis diffuse reflectance spectroscopy (UV–Vis-DRS), field emission gun-scanning electron microscopy (FEG-SEM), energy-dispersive spectroscopy (EDS) and photoluminescence spectroscopy (PL), respectively. The detailed structural study reveals the formation of the cubic structure with space group pm3m for pristine and Ga-doped CH3NH3PbCl3 perovskites. Microstrain and lattice dislocation density of doped perovskites increase with increasing Ga composition, compared to the undoped CH3NH3PbCl3. Optical properties show the bandgap narrowing up to 10% Ga doping, and any further increase in doping concentrations again increases the bandgap. This blue shift in absorption edge, i.e. bandgap widening behaviour, of highly doped CH3NH3PbCl3 (20% and 30%) perovskites justifies the Burstein–Moss effect in doped semiconductors. The highest Urbach tail energy is observed for 10% Ga-doped compound, which in turn results in the highest electron–phonon interaction. Morphological imaging shows that optimum Ga doping (10%) can improve the characteristic in terms of homogeneity and defect-free surface, compared to pristine perovskite. However, doping beyond the optimal value can further deteriorate the surface morphology by enhancing the surface inhomogeneity and defects. XRD and EDS both confirm the purity of the synthesized materials. Here, doping increases non-radiative recombination which suppresses the radiative recombination of pure CH3NH3PbCl3. These observations unfold the prospect for a new insight of post-transition metals, to fabricate lead-free perovskite materials with advanced optoelectronic properties.