Tobechi Okoroafor

Thin film solar cells offer several benefits over conventional first-generation technologies including lighter
weight, flexibility, and a wider range of optoelectronic tunability. Their environmental impact however needs to be investigated comprehensively to provide a clear comparison point with the first generation photovoltaics currently dominating the market. The main objective of this review is to evaluate current Life Cycle Assessment (LCA) studies conducted on thin film solar cells, highlighting the key parameters considered including life cycle stages, impact categories, and geographical locations. This included both commercially available thin film solar cells (a-Si, CIGS, CIS, CdTe, GaAs and GaAs tandem) as well as emerging (PSC, PSC tandem, DSSC, OPV, CZTS, QD) ones. A critical assessment of the results of 58 LCA studies was conducted and compared with traditional silicon based solar cells. Results indicate that emerging thin film solar cells hold great promise, as they tend to perform better than commercially available ones in the specified indicators, especially for CZTS and OPV. The assessment demonstrated that overall thin film solar cells had less energy requirement and better environmental performance than conventional crystalline silicon solar cell systems. However, due to their lower efficiencies, their energy payback time was higher. This review provides a benchmark for the environmental LCA of different thin film solar cell technologies in order to highlight the relevance of these devices for sustainable energy generation and to give manufacturers and LCA experts information and a basis for future evaluation of solar cells.

Nano-structured fumed silica (FS) is the most used vacuum insulation panel (VIP) core material for building applications. However, the FS VIP core has the majority of the environmental burden associated with conventional VIP manufacture and FS-based VIPs are very expensive. This paper explores aluminium anodizing sludge (ALW), a residue from the aluminium industry, as a new substitute for FS in VIP cores. Al-rich sludge waste is thoroughly characterised, and 100%-based ALW and its hybrid core mixtures with FS are formulated to produce VIPs cores, which are then evaluated. ALW was observed as aggregated clusters of nanosized individual particles in round and smooth-shaped forms typical of hydrated gel-like pure amorphous materials. The microstructure system of the sole ALW VIP core is found to be dissimilar to that of an FS VIP core, with the pore size range of 0.1–0.8 μm for the former and 0.01–0.04 μm for the latter, but the overall volume of large pores being much higher for the FS than ALW cores. The hybridization of ALW and FS resulted in a restructure of the initial ALW core systems. While the thermal conductivity of the ALW VIP core is less proficient than that of the single FS core, the effective thermal conductivity of both ALW50FS50 and ALW25FS75 core compositions at 1 Pa even suppressed that of the sole FS core, presenting 5.8 mW m−1·K−1 against 6.3 mW m−1·K−1 respectively. A life cycle assessment (LCA) study of these hybrid core solutions was also conducted to illustrate the positive environmental benefit of ALW-based VIP compared to FS-based VIP production. The study highlights the potential of using industrial residue ALW in VIP production, contributing to developing more sustainable superinsulation materials.

Kesterite-based structures are being extensively studied for solar module productions due to their earth abundant and nontoxic nature, high absorption coefficient, and a wide variety of scalable deposition methods. Kesterites are mostly manufactured using thin-film technology. However, in the last decade, the monograin approach has gained further attention, providing a third alternative to mono-crystalline wafer and thin film methods. This is due to its high throughput, low-cost deposition techniques, flexibility, and light weight. Despite the technical advancements in the monograin technology, their environmental impacts have not been studied in the literature. This paper, for the first time, presents a cradle to gate environmental life cycle assessment of CZTS monograin module production. The analysis is designed to identify the environmental hotspots associated with materials, energy usage, and manufacturing processes. The results were compared to CZTS thin-film and the commercially available CIGS technologies. The analyses suggested that the front contact accounted for the majority of impact in all categories due to the use of silver. The normalisation results showed that the marine aquatic ecotoxicity impact category dominated the overall impact results. A comparison of CZTS monograin and thin film production demonstrated that monograin outperformed the thin film technology when silver was substituted with alternative materials and was proximate to CIGS even considering their higher achieved efficiency. The analysis presents considerable environmental benefits associated with the monograin technology. Further savings in emissions could be achieved with improved conversion efficiency and usage of renewable energy sources in the manufacturing stages.

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Perovskite solar cells (PSCs) have moved to the forefront of emerging thin-film solar cell research in just a
decade, demonstrating the most promising efficiency records. These technological advancements however, were primarily tested at laboratory scale and there remains significant issues in relation to the scalability of the deposition methods utilised. Inkjet printing, initially used for printed electronics, has recently been applied to solar cell production and demonstrated promising potential for scaling up. Despite various studies that have assessed the technical feasibility of utilising inkjet printing, their environmental performance has not been investigated. This paper, for the first time, presents a comprehensive Life Cycle Assessment (LCA) study of inkjet printing-based PSCs, on a cradle-to-gate basis using GaBi LCA software. The results were compared with those of spin-coating, as the most widely studied deposition method, and demonstrated significant improvement in all impact categories. Global warming potential (GWP) and cumulative energy demand (CED) were used as proxies to compare results obtained in this paper with available studies in the literature. The comparison demonstrated that inkjet printing of PSCs had a GWP and CED of 7.54 kg CO2eq/m2 and 200.18 MJ/m2 while spin-coating had a reported median value of 74.5 kg CO2eq/m2 and 1204 MJ/m2 respectively. This suggests considerable environmental advantage for the inkjet method. The paper also assesses a novel green solvent-based precursor ink investigating the environmental benefits of eliminating the toxic and hazardous solvent materials commonly used in wet chemical deposition of perovskite layers. The green solvent-based precursor ink results demonstrated
significant improvement over conventional solutions with up to six orders of magnitude lower impacts. The LCA results obtained in this paper contributes to forming a full assessment of the development of scalable deposition methods such as inkjet printing by highlighting their environmental hotspots and advantages. The paper also identifies potential opportunities for perovskite precursor ink material composition improvements for sustainable development of PSCs. This will assist in addressing their associated environmental concerns in relation to the use of high-impact toxic solvents.

Thin-film photovoltaics (PV) cells offer several benefits over conventional first-generation PV technologies, including lighter weight, flexibility, and lower power generation cost. Among the competing thin-film technologies, chalcogenide solar cells offer promising performance on efficiency and technological maturity level. However, in order to appraise the performance of the technology thoroughly, issues such as raw materials scarcity, toxicity, and environmental impacts need to be investigated in detail. This paper therefore, for the first time, presents a cradle to gate life cycle assessment for four different emerging chalcogenide PV cells, and compares their results with copper zinc tin sulfide (CZTS) and the commercially available CIGS to examine their effectiveness in reducing the environmental impacts associated with PV technologies. To allow for a full range of indicators, life cycle assessment methods CML 2001, IMPACT 2002+, and ILCD 2011 were used to analyse the results. The results identify environmental hotspots associated with different materials and components and demonstrate that using current efficiencies, the environmental impact of copper indium gallium selenide (CIGS) for generating 1kWh electricity was lower than that of the other studied cells. However, at comparable efficiencies the antimony-based cells offered the lowest environmental impacts in all impact categories. The effect of materials used was also found to be lower than the impact of electricity consumed throughout the manufacturing process, with the absorber layer contributing the most to the majority of the impact categories examined. In terms of chemicals consumed, cadmium acetate contributed significantly to the majority of the environmental impacts. Stainless steel in the substrate/insulating layer and molybdenum in the back contact both contributed considerably to the toxicity and ozone depletion impact categories. This paper demonstrates considerable environmental benefits associated with non-toxic chalcogenide PV cells suggesting that the current environmental concerns can be addressed effectively using alternative materials and manufacturing techniques if current efficiencies are improved.

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