Hybrid organic-inorganic lead halide perovskites (i.e., methylammonium lead trihalide, CH3NH3PbX3 also known as MAPbX3, where MA = methylammonium or CH3NH3, and X = Cl, Br, or I) have garnered significant attention involving electronic, optoelectronic, laser, lightemitting diode, photodetector, and X-ray/γ-ray detector device technologies. This is largely due to tunable process-dependent compositions, structures, and morphologies resulting in a wide range of material characteristics, such as changes in the bandgap, carrier mobility, and exciton binding energy. Additionally, the potential for adaptable low-cost manufacturing (compared to state-ofthe-art commercial technologies) make perovskites appealing for high-production through-put and scale-up manufacturing advancements. However, material and device development challenges impact the broader adoption of perovskite material integration at scale-including stability and durability limitations, material quality and property performance reproducibility, environmental or defect degradation, induced toxicity, and controlled synthetic scale-up methodologies. As such, it is common to observe a wide range of reported material properties that impact the electrical responses and optical characteristics of MAPbX3. Such structure-property-processing effects complicate electronic and optoelectronic device design and development optimization strategies for commercialization. The most prominent application focus for halide perovskites is the development of highperformance, low-cost solar cells. Hybrid organic-inorganic lead halide perovskite solar cells (PSCs) have been shown to achieve a power conversion efficiency (PCE) of over 25%, which rivals state-of-the-art high-performance silicon solar cells (≥25% PCE). Critical to the development of PSCs are the optical properties (refractive index, n, and extinction coefficient, k) of the halide perovskite active layer, which describe the way materials interact with light and subsequently function as a photovoltaic material. Proper derivation of perovskite optical constants enables the optimized design of efficient solar cells. While there are many considerations when designing an exemplary PSC (e.g., compositional bandgap tuning, surface nano or microstructured light trapping, multilayer tandem cell architectures, and enhanced charge carrier extraction), perhaps the most important device consideration is the perovskite layer absorptance within the given solar cell architecture. Perovskite optical absorptance in a solar cell device directly impacts the efficacy of solar radiation absorption for an engineered PSC and the resulting PCE.