Since their first reported use (Kojima, Miyasaka 2009), solution-grown lead halide perovskite (LHPs) thin films have been studied extensively as viable alternatives to conventional solar cell materials. Solution-processed LHPs provide platforms to tailor the photoactive layer to achieve high power conversion efficiencies (PCEs), tunable band gaps, and high charge carrier mobilities with long diffusion lengths. One of the most crucial aspects of translating perovskite thin film research from the lab to industry is our ability to achieve precise control over the solution and crystalline states. Fabricating phase-pure, uniform, crystalline thin films with complete coverage on the target surface, however, remains a challenge given the complexities that arise from multiple competing phenomena. Some of the commonly observed phenomena include irreproducibility between batches, labs and users; undesired intermediates or solvates; de-wetting; uncontrolled nucleation or growth; or pinholes in the final thin films. Gas-quenching as an alternative to antisolvent quenching has seen great interest in achieving reproducibility at the laboratory scale. I employed a two-step nitrogen gas-quenching protocol for fabricating spin-coated organic-inorganic LHP thin films. Of the expansive parameter space that stems as a result, I chose to investigate the effects of solvent and quench conditions for making mixed Cs$x$FA${1-x}$Pb(I${1-x}$Br$x$)$3$ perovskite thin films. The hybrid formamidinium and cesium double cation combination provides better thermal stability, improved band gaps, and better stability of the $\alpha$-phase compared to pure-cesium and pure-formamidinium-based systems. Formamidinium has been shown to orient faster in the crystal lattice than conventional methylammonium cations leading to better orbital interactions and more stable optoelectronic properties. Bromide and iodide for mixed halide perovskites offer greater band gap tunability and reduced charge recombination with increased lifetimes. Through this thesis I assert that solution-processed lead halide perovskites are sensitive to processing conditions and exhibit unique behaviors as a function of the solvent choice and the time delay before the injection of the quenching gas ($t{\mathrm{quench}}$). For the first time I report using solvent blends and $t{\mathrm{quench}}$ to tailor perovskite thin films with different characteristic traits. I report a robust method with successful perovskite formulations that can be used to conduct further optoelectronic studies. Scanning electron microscope (SEM) images revealed grain and defect distributions that changed with $t{\mathrm{quench}}$. Shifts in the peak positions observed in X-ray diffraction (XRD) experiments revealed changes in the $d$-spacing of the perovskite crystal. Variance in the relative peak intensities between thin films made from different conditions provided insights on preferred crystal orientation and crystal texturing. XRD and SEM data provided qualitative insights about the thin films. Optical band gaps calculated from UV-visible (UV-Vis) spectra of the thin films displayed significant deviations based on the solvent blend. I further studied the thin films with inductively coupled mass-spectrometry (ICP-MS) to get quantitative insights about the Pb:X and Pb:Cs ratios in the thin films. My findings could be used to fabricate high-quality phase-pure thin films with complete coverage, desired grain size distributions, morphologies, crystal textures, bandgaps and even defect profiles. My findings show that, through strategic optimization, we can probe and understand the optoelectronic properties of lead halide perovskite thin films and contribute to the development of high-performance solar cells.