With increased efficiency, simplicity in manufacturing, adaptability, and flexibility, solar cells constructed from organic metal halide perovskite (PVK) have recently attained great eminence. Lead, a poisonous substance, present in a conventional PVK impacts the environment and prevents commercialization. To deal with this issue, a number of toxicity-free PVK-constructed solar cells have been suggested. Nevertheless, inherent losses mean the efficiency conversion accomplished from these devices is inadequate. Therefore, a thorough theoretical investigation is indispensable for comprehending the losses to improve efficiency. The findings of a unique modelling method for organic lead-free solar cells, namely methylammonium tin iodide (MASnI3), are investigated to reach the maximum practical efficiencies. The layer pertinent to MASnI3 was constructed as a sandwich between a bio-synthesized electron transport layer (ETL) of CeO2 and a hole transport layer (HTL) of CuCrO2 in the designed perovskite solar cells (PSCs). In this study, the use of algae-synthesized Au in the back contacts has been proposed. To obtain the maximum performance, the devices are further analyzed and optimized for active layer thickness, working temperature, total and interface defect density analysis, impedance analysis (Z′-Z), and capacitance-voltage (C-V), respectively. An optimal conversion efficiency of 26.60% has been attained for an MASnI3-constructed PSC. The study findings may open the door to a lead-free PSC through improved conversion efficiencies.