All-inorganic cesium lead-halide perovskite thin films show great promise for optoelectronic applications. This study introduces a novel synthesis strategy for CsPbBr3 thin films, conducted on a preheated substrate. The synthesis process involves precise control and optimization of parameters under ambient conditions, eliminating the need for a glovebox. Therefore, a facile and low-cost way to fabricate CsPbBr3 perovskite thin films for potential optoelectronic applications has been provided by this method. The effects of various parameters, such as precursor concentration, annealing temperature, and polyethylene oxide (PEO) addition, on the structure, morphology, and optical properties of the perovskite films were systematically studied. The optimal conditions for the highest photoluminance and maximum surface coverage were found to be 0.26 M precursor concentration, 100 °C annealing temperature, and 100:65 CsPbBr3:PEO weight ratio. Uniform and bright perovskite films with over 99% surface coverage, reduced grain size, and suppressed trap density were obtained as a result of these conditions. The PL intensity of the optimized composite thin film exhibited a minor decrease of 6% from its initial value over six months in an ambient environment. A proof-of-concept perovskite light-emitting electrochemical cell (PeLEC) was constructed utilizing the optimized single-layer perovskite thin film. Consequently, green electroluminescence at 523 nm, featuring a full width at half maximum (FWHM) of 20 nm and a chromaticity coordinate of (0.121, 0.800), was successfully generated from the PeLEC. This showcases the viability of the mentioned methodology for the future fabrication of light-emitting devices.