Investigation of Physico-Chemical Properties of CH3NH3PbI3 and CH3NH3PbI3–xClx Hybrid Perovskites Thin Films for Photovoltaic and Optoelectronic Applications: A Comparative Study

Abstract

CH₃NH₃PbI₃ and CH₃NH₃PbI_3–xCl_x, hybrid perovskites thin films were grown on glass substrates employing spin-coating technique at different rotational speeds varying from 1000 to 2000 rpm. All the films exhibited a polycrystalline tetragonal structure with a preferred (110) orientation. For each rotational speed, the CH₃NH₃PbI₃ and CH₃NH₃PbI_3–xCl_x films had approximately the same order of the absorbance in the visible region of solar spectrum. The current–voltage measurements of the CH₃NH₃PbI₃ and CH₃NH₃PbI_3–xCl_x films showed a ferroelectric hysteresis behavior in the dark which it becomes Ohmic under the illumination indicating the microstructural improvement. The all samples were strongly resistive in the dark, and their electrical conductivity improving thousands of times under the illumination; it had varied in the ranges 25.5 × 10^–3‒206.61 (Ω cm)^–1 and 82.81 × 10^–3‒689.47 (Ω cm)^–1 for CH₃NH₃PbI₃ and CH₃NH₃PbI_3–xCl_x, respectively. Our results demonstrated that the 1000 and 2000 rpm were optimal parameters for CH₃NH₃PbI₃ and CH₃NH₃PbI_3–xCl_x films preparation, respectively. Moreover, the addition of the chlorine in CH₃NH₃PbI₃ films improves their physico-chemical properties. Indeed, compared to the CH₃NH₃PbI₃ prepared at 1000 rpm, the CH₃NH₃PbI_3–xCl_x film synthesized at 2000 rpm had the thinner thickness 571.58 nm, largest crystallite size 204.81 nm, lesser dislocation density 2.38 × 10^–5 lines nm^–2, superior quality of surface morphology, higher band gap 1.53 eV, lower Urbach energy 276.23 meV, higher refractive index 2.96, higher electrical conductivity in the dark 82.81 × 10^–3 (Ω cm)^–1 and under the illumination 689.47 (Ω cm)^–1. CH₃NH₃PbI_3–xCl_x thin film synthesized at 2000 rpm has better quality that might be more suitable as a light absorbers films for photovoltaic cells and optoelectronic devices.