CONTROLLED CRYSTALLIZATION OF INORGANIC PEROVSKITE SEMICONDUCTOR THIN FILMS VIA SOLUTION PROCESSING METHODS

Abstract

Inorganic perovskite semiconductors have recently gotten great concern in the field of photovoltaics due to their excellent optoelectronic properties such as a superb carrier dispersion span, resilient light absorption intensity, low defect density, solution processability, narrow spectral bandwidth, and halide composition, tuneable direct band gap, covering the visible spectral range, high photoluminescence quantum yields, and high absorption coefficient. Perovskite materials are susceptible to degradation from heat, light, and moisture. On the other hand perovskite material can undergo a phase change from the optically active 𝛼-phase to the yellow 𝛿-phase. A decrease in the performance and lifetime of the photovoltaic nanotechnology accompanies this phase transition. The above challenges can lead to disturbance in the applications of photovoltaic devices. To overcome the problems, we set objectives such as self-doping of all inorganic Cesium lead iodide film and treated with additives, doping mixed lead halide perovskite with silver bromide, and treating mixed halide perovskite film by mixed antisolvent. Experimentally, we used a solution processing method through a one-step spin-coating process, and theoretically, we examined the microelectronic crystal structure of the unit cell of the material by density function theory (DFT) and theoretical calculation based on Flory-Huggins theory. The optical properties of the film were characterized by ultraviolet-visible spectroscopy, photoluminescence spectroscopy, and time-correlated single-photon counting (TCSPC) spectroscopy. X-ray diffraction (XRD) characterized the films' crystal structure. An infrared spectrum of emission and absorption of the perovskite film demonstrated by Fourier transform infrared (FTIR) spectrometry. The microstructure of the film's morphology was studied by Field emission scanning electron microscopy, transmission electron microscopy (TEM), and atomic force microscopy. Primarily, we demonstrate self-doped cesium lead iodide film and treated by organic additives. In this case, the complete homogeneity of additive-solvent showing higher critical solution temperature (HCST) behavior is for both different additive-solvent mixtures chloronaphthalene: Dimethyl formamide > Octanediithiol: Dimethyl formamide > Diethyl octane: Dimethyl formamide. When1, 8-diiodooctane (DIO), and 1-chloronaphthalene (CN) were used as stabilizers the manifestation process was improved prerequisite to the formation of an appropriate bandgap improvement to 1.76eV (doping with CN), 1.78eV (doping with DIO) from 1.83 eV (undoped). Secondly, we doped cesium lead mixed halide (CsPbI2Br) perovskite film by varying silver bromide (AgBr) concentration to study the consequence of AgBr on the perovskite film. The bandgap tenability as a function of the silver doping level xii using density function theory through half substitution of lead by silver, and experimentally with varying AgBr concentrations in the precursor solution of perovskite film. Resultantly, the film maximized the bandgap value from ~1.87 eV to ~1.96 eV. The lifetime of the film was increased from 0.99ns (undoped) to 1.187 ns (doped with AgBr). Generally from investigation, we found that doping with an appropriate concentration of silver bromide (AgBr) resulted in improved phase purity, increased crystallinity, uniform film coverage, and changed surface morphology. Finally, we investigate the effect of mixed polar antisolvents (mixed toluene with ethyl acetate) on cesium lead mixed halide perovskite film. Resultantly, the observed phase similarity indicated that the mixed CsBr in the perovskite film had no negative effect, miscible in precursor solution uniformly, and increased the crystalline size. From the overall demonstration, the perovskite film has improved optically, structurally, and morphologically. Finally, the self-doping method with additive manufacturing, doping silver bromide with all inorganic perovskite, and treating mixed halide perovskite with mixed antisolvent ought to help to produce a black γ-phase perovskite for light absorbing material in ambient conditions.