Compositional engineering of Perovskite materials to replace toxic lead (Pb) in photovoltaic applications

Abstract

Solar energy is a renewable and environmentally friendly power source that is free from pollution and noise, making it a promising alternative to conventional non-renewable energy sources. Solar cells are extensively used to efficiently harness and convert sunlight into electricity, offering substantial potential for sustainable energy generation. Among the various types of solar cells, Organolead halide perovskite solar cells have garnered considerable attention in recent years due to their superior optoelectronic properties. However, Pb is highly toxic, and the dissolution of lead (Pb) in water poses serious environmental and health risks and long-term instability, hindering commercialization. Thus, the development of stable, lead-free perovskites is critical. The thesis presents a first-principles Density Functional Theory (DFT) investigation of the structural, electronic, and optical properties of bismuth-based halide perovskites, chalcogenide halide perovskites, and chalcohalides as Pb alternavites. A detailed theoretical and numerical analysis is conducted on materials including CH3NH3BiI2Se, CH3NH3BiI2S, Sb1-xBixSeI, Cs3Bi2I9 and CH3NH3Bi2I9. Among these, CH3NH3BiI2Se exhibited a higher absorption coefficient, broader spectral absorption, and superior charge carrier mobilities compared to CH3NH3BiI2S, with corresponding power conversion efficiencies (PCEs) of 24.06% and 21.85%, respectively. The bandgap tuning in Sb1- xBixSeI, achieved through increased Bi content, enhanced light absorption and carrier transport, making Sb0.4Bi0.6SeI a promising absorber material for thin-film solar cells. Additionally, numerical simulations of Cs3Bi2I9 and CH3NH3Bi2I9 based perovskite solar cells revealed the significant influence of defect densities on device efficiency, with optimized Cs3Bi2I9 based PSCs achieving a PCE of 13.81%. Above findings from the compositional engineering of materials contribute to a deeper understanding of structure and property relationships in bismuth-based chalcohalides and provide valuable insights for the design of lead-free, non-toxic, and sustainable optoelectronic devices. This work paves the way for the development of environmentally friendly materials tailored for next- generation photovoltaic technologies