Towards Circular Photovoltaic Modules: Selective Material Recovery and Bio-Based Encapsulant Development

Abstract

Abstract As cumulative photovoltaic (PV) installations approach 75 TW by 2050, the industry faces an end-of-life (EoL) material burden projected to reach 54-160 Mt. Conventional mass based recycling effectively downcycles these modules, recovering bulk glass and aluminium while discarding the metallic fractions that concentrate most of the recoverable value. This thesis addresses chemistry, process, and material solutions at three points along the module life cycle. First, a sequential aqueous chemistry was developed to recover silver and aluminium from monocrystalline silicon cells without bulk dissolution. Sodium hydroxide (NaOH) removes the rear aluminium contact and ferric chloride (FeCl3) then detaches the silver busbars as intact metallic strips, recovered by filtration at 93% yield. Benchmarked against the conventional nitric acid (HNO₃) process and a choline chloride (ChCl) process, life cycle assessment (LCA) shows a 75% reduction in climate-change burden (ReCiPe 2016 midpoint, kg CO₂ eq/kg) relative to the conventional process, while techno-economic assessment (TEA) at 10,000 tonnes per year identified a net deficit of €1.56 per module, with silver accounting for 45% of revenue. This work then demonstrates laser-assisted of EVA delamination on multicrystalline silicon modules aged 10 to 13 years in outdoor service. A 1064 nm pulsed fibre laser is used here to disrupt the EVA–silicon interface directly, separating the laminate into three streams: intact EVA film, isolated busbars, and a silicon-rich powder. The powder is then processed through sequential alkaline and chloride-based leaching, recovering silver at greater than 99% selectivity for the REC240PE module and greater than 95% for the CS6P-245P. Finally, a castor oil polyurethane crosslinked with an aliphatic hexamethylene diisocyanate (HDI) trimer was synthesised as an encapsulant. The cured network absorbed 0.31% water (three times lower than a fossil-based control). Under 1 Sun illumination, encapsulated passivated emitter and rear contact (PERC) cells retained their open-circuit voltage and fill factor, with an optical reduction in power conversion efficiency (2.6% relative to the bare cell). Accelerated ageing over 1000 h (QUV at 60 °C; dark dry heat at 80 °C) identified thermo-oxidative attack on the castor oil double bonds as the dominant degradation pathway. Laser debonding at 1064 nm released the cured polyurethane largely intact within a 30–35% power window, with the sintered silver grid preserved and the pyramidal silicon texture largely retained. This work provides process and material evidence to assist in implementing scalable circularity for crystalline silicon PV ahead of these projected waste volumes.