Perovskite solar cells (PSCs) are one of the most popular and got attention of the photovoltaic researchers of the twenty-first century. It is well characterized by their high-power conversion efficiency (PCE), adjustable bandgaps, and cost-effective production methodology. But, heavy use of toxic lead (Pb)-bearing in the active absorber layer has create considerable alarm over their environmental and toxicological impacts, thus initiation to transit from lead to lead-free substitutes. This chapter provides in-depth investigation of design principles of lead-free PSCs, with their syntheses process, performance trends, challenges, and prospects. Promising material like tin (Sn), germanium (Ge), bismuth (Bi), antimony (Sb), silver (Ag), copper (Cu), double perovskites, and chalcogenides are evaluated in terms of structural robustness, electronic quality, scalability, and environmental friendliness. The results show that Sn-based perovskites surpass 15% efficiency, but affected by oxidation hence accelerate degradation. Bi- and Sb-double perovskite films provide strong long-term stability, but efficiency is low due to large bandgaps; while chalcogenides exhibit high robustness in extreme conditions, but processing technology are complex. We cover syntheses such as solution deposition, vapor deposition, and environmentally friendly syntheses, noting them closely in terms of scalability and integrability in a device layer. The chapter further covers key market debut constraints, that is, intrinsic material unitability, efficiency plateaus, scalability issues, toxicities, and non-existence of standard recycling protocols. Also, prospects such as alloy engineering, 2D/3D hybrid geometries, computer-aided materials discovery, tandem schemes, and environmentally friendly syntheses reveal identified avenues to address such constraints. The chapter provides a comprehensive analysis potential for commercialization of lead-free PSCs replace Pb-containing PSCs. Also, their great potential for commercialization, such as indoor solar cells, flexible electronics, and usage in space or desert regions are discussed. Finally, the development of lead-free perovskite solar cells with using emerging technologies to achieve higher efficiency, good stability, and environment-friendly counterparts.