This dissertation explores the eco-design concepts for emerging PV cells. By conducting life cycle assessment (LCA) method, I addressed the following questions: (1) What is the environmental impact of a scalable perovskite PV cell? (2) How important are the metal emissions from the emerging thin film devices during the use phase? (3) What are the environmental impacts and costs of the materials used in emerging PVs? These questions are addressed in the analyses presented in the Chapters two, three and four, respectively.
Chapter two assesses the environmental impacts of perovskites PVs that have device structures suitable for low cost manufacturing. A structure with an inorganic hole transport layer (HTL) was developed for both solution and vacuum based processes, and an HTL-free structure with printed back contact was modeled for solution-based deposition. The environmental impact of conventional Si PV technology was used as a reference point. The environmental impacts from manufacturing of perovskite solar cells were lower than that of mono-Si. However, environmental impacts from unit electricity generated were higher than all commercial PV technology mainly because of the shorter lifetime of perovskite solar cell. The HTL-free perovskite generally had the lowest environmental impacts among the three structures studied. Solution based methods used in perovskite deposition were observed to decrease the overall electricity consumption. Organic materials used for preparing the precursors for perovskite deposition were found to cause a high marine eutrophication impact. Surprisingly, the toxicity impacts of the lead used in the formation of the absorber layer were found to be negligible.
Chapter three addresses the life cycle toxicity of metals (cadmium, copper, lead, nickel, tin and zinc) that are commonly used in emerging PVs. In estimating the potential metal release, a new model that incorporates field conditions (crack size, time, glass thickness) and physiochemical properties (diffusion coefficient and solubility product) was introduced. The results showed that the use phase toxicity of copper and lead can be more toxic than that of the extraction phase. Thus, precautionary loss limits to manage toxic impacts from the use phase was proposed. Also, the toxicity from different layers of perovskite, copper zinc tin sulphide (CZTS), and quantum dot (QD) type of solar cells was compared. It was found that cadmium sulphide (compared to zinc oxide and tin oxide) and lead (II) sulphide (compared to lead (II) iodine and CZTS) were less toxic alternatives for electron selective layer and light absorber, respectively. Finally, in comparing the toxic metal releases of the PVs to today’s coal power plants, it was seen that the metal emissions from PVs are expected to be several times less than the emissions from coal.
Chapter four aims to create inventories that offer insight into the environmental impacts, and cost of all the materials used in emerging PV technologies. The results show that CO2 emissions associated with the absorber layers, are much less than the CO2 emissions associated with contact and charge selective layers. CdS (charge selective layer) and ITO (contact layer) have the highest environmental impacts compared to Al2O3, CuI, CuSCN, MoO3, NiO, P3HT, PCBM, PEDOT:PSS, SnO2, Spiro-OMeTAD, and TiO2 (charge selective layers) and Al, Ag, FTO, Mo, ZnO:In, and ZnO/ZnO:Al (contact layers). The cost assessments show that the organic materials such as polymer absorber, CNT, P3HT and Spiro-OMeTAD are the most expensive materials. Inorganic materials would be more preferable to lower the cost in solar cells. All the remaining materials have a potential to be used in commercial PV market. Finally, the eco-efficiency analysis showed that absorbers made from polymer, and CNT, charge selective layers made from Spiro-OMeTAD, PCBM and CdS and contact layers made from ITO, ZnO:In, and ZnO:ZnO:Al materials should be excluded from emerging PV market to lower the cost and environmental impacts from solar cells.