Theoretical evaluation of metal release potential of emerging third generation solar photovoltaics

With rapid growth in solar industry, the potential fate and management of solar modules has raised concerns due to the presence of few toxic metals. Present work addressed this issue by (i) estimating potential release values (solubility product, Ksp at pH 7) of various compounds used in different layers of emerging solar cells in neutral water and landfill leachate conditions, and (ii) further comparing their metal release values (termed as loss factors, LFs, hereafter) with that of first and second generation photovoltaics. Top five compounds with highest metal release probability (probability>0.5) were found to be: PbI₂(highest LF)> CuI> Cd(OH)₂> CuSCN> CdO (smallest LF). Also, the identified compounds with lowest risk were: PbSe <Sb₂S₃ <CdSe <Al₂O₃ <SnS (lowest probability: 10⁻¹⁰ to 10⁻¹⁶). With respect to solar cells, perovskite solar cells were ranked first in terms of hazard as it mostly contains compounds like PbI₂, CuSCN, CuI, NiO, and Al₂O₃. Quantum dot solar cells were ranked second due to presence of category II compounds (i.e., ZnO). Further, the organic and dye-sensitized solar cells are of least concern as they do not contain compounds with high LF values. With respect to different layers of an emerging PV, electron- and hole-transport layers were found to be with highest risk for material release. With respect to third generation solar cells, metal LFs for first generation solar cells were less for lead, cadmium and copper. Following the conservative approach, the calculated conversion factors for metal loss values from neutral water (pH7) to landfill leachate (i.e., CFs = LF_{MSW leachate}/LF_pH7) for Pb (0.075), Cu (0.263), Ni (0.426), Zn (0.591) were used for estimating metal loss values from emerging solar cells in landfill leachate conditions. Among all generation solar PVs, mostly lead-containing compounds were found to be exceeding the LF cut-off values. Thus, perovskites solar cells with lead–based compounds might pose risk to groundwater or surface runoff due to lead.