The transition to renewable energy, led by photovoltaic (PV) energy, is critical for a sustainable future. However, the current linear ”take-make-waste” economy, also used for PV modules, presents a significant challenge to long-term sustainability, creating a massive future waste stream and reliance on virgin materials. The primary obstacle to achieving a circular economy for solar modules is the use of permanently cross-linked solid encapsulants like Ethylene Vinyl Acetate (EVA), which bond all components together and severely hinder repair, reuse, and high-value recycling. This thesis examines liquid encapsulation as a promising alternative design-for-recycling concept, enabling simple disassembly and material recovery. The primary objective was to determine if liquid encapsulation is a viable alternative from an optical perceptive, compared to conventional solid (EVA) and gas-filled (air) module designs. To achieve this, three sub-goals were formulated and completed. First, a comprehensive selection strategy was developed based on critical optical, electrical, chemical, and thermal criteria, identifying seven candidate liquids for analysis: deionised water, glycerol, SolaPro Ennogreen glycol, Polydimethylsiloxane (PDMS), and three industrial dielectric oils (Shell Diala S4 XZI, Midel 7131, Mivolt). Material compatibility tests with polyisobutylene (PIB) immersed in Midel 7131 and Shell Diala, confirmed that Shell, and therefore mineral oils in general, are incompatible with the use of PIB as a sealant. Second, the complex refractive index (n and k) of these liquids was experimentally measured over the 300–1200 nm solar spectrum using a novel hybrid method. This involved a specialised ellipsometer and dual cuvette measurements with spectrophotometry, generating the nk data needed for detailed optical modelling. Measurements made by Semilab’s liquid-specialised ellipsometer using a 2-term Cauchy model yielded excellent fits (R2 > 0.97) for all liquids, in good agreement with literature values. The dual cuvette method revealed extremely high transparency for all liquids, even slightly yellowish fluids Midel and Shell Diala. A SNR analysis established a confidence threshold at k ≈ 5 ∗ 10−8. Finally, these optical properties were used as inputs for detailed optical modelling and simulation, in GenPro4, to quantify and compare the photocurrent generated by liquid encapsulation compared to standard EVA and air, in various solar module configurations. The optical model and its simulated output are validated through experiments and datasheets, showing excellent agreement around the Δ Jph = 0.2 mA/cm2. The results revealed a fundamental trade-off: while the liquids have lower refractive indices, leading to higher initial reflection losses compared to conventional EVA with UV blockers, their superior transparency resulted in lower parasitic absorption. This balance allowed top-performing liquids, notably Mivolt (highest photocurrent and lowest reflector, Jph = 40.90 41.81 mA/cm2) and PDMS (lowest absorber, Jph = 40.85 41.75 mA/cm2), to generate a photocurrent comparable to, and in some cases higher than, UV-transparent EVA (Jph = 40.92 41.81 mA/cm2). However, the optical performance of the other liquids was very close (especially Midel and Shell, but also glycerol and glycol, followed within 0.17 mA/cm2), meaning that based on optics alone, they should not be excluded, as other design benefits might justify their selection. A critical insight emerged from annual energy yield simulations, which demonstrated that PDMS delivered the highest yearly energy output (0.07% higher than EVA-UVT, 0.086% to Mivolt), due to its extremely low absorption. The simulations showed that mitigating reflection losses through tailored Anti-Reflection Coatings (ARCs) or glass texturing can further unlock the full potential of liquid-encapsulated modules. In conclusion, this thesis provides the first comprehensive optical validation for liquid encapsulation in standard silicon PV modules. It successfully demonstrates that, from an optical standpoint, liquids are a highly viable technology, worthy of further research. Their primary drawback of higher reflection is compensated by superior transparency and can also be further mitigated with existing ARC and glass texturing technologies. This work establishes a robust foundation for future research, confirming that liquid encapsulation is not only a promising pathway toward a circular economy for PV but is also an optically competitive alternative to established solid encapsulants.

With the enormous rise in installed photovoltaic (PV) modules over the past decade, it is to be expected that soon, a massive increase in decommissioned PV modules will arise. Current PV modules are difficult and energy-intensive to recycle, leading to some of the most valuable materials going to waste. To prevent this, new PV module structures have been proposed, with the most promising structure containing a layer of air between the module’s front glass and the solar cell. Due to this replacement of the ethylene vinyl acetate (EVA) layer, the air-filled modules are easier to disassemble and recycle. However, it lowers the module efficiency due to a mismatch in the refractive index of the front glass and air. To overcome the refractive index mismatch of air-filled modules, this study evaluates the performance and degradation behaviour of self-manufactured, liquid-filled PV modules, which are subjected to humidity freeze accelerated ageing and their results are compared to air-filled and EVA-laminated mod-
ules. To achieve this, suitable liquids are selected. Subsequently, several one-cell mini-modules are hand-manufactured, which are filled with air, the selected liquids, and laminated with EVA. The results are obtained by subjecting the modules to 30 cycles of humidity freeze testing and by measuring their electrical characteristics under standard testing conditions. Initial performance measurements show that all four tested liquids, including water (3.7%), polydimethylsiloxane (PDMS) (6.2%), mono propylene glycol (MPG) (5.1%), and glycerol (5.1%), offer substantial efficiency improvements over air-filled modules, with PDMS even slightly outperforming EVA (5.5%). A major point of failure is the PIB edge seal, especially at the liquid injection points, indicating a need for improved manufacturing techniques. The module failures also allowed for disassembly trials, which show that liquid-filled modules can be completely disassembled with ease, allowing for full material recovery. This highlights the reusability potential of liquid-filled designs due to the absence of more permanent encapsulant layers like EVA. The humidity freeze accelerated ageing, subjects the modules to extremely low and high temperatures of -40 °C and 85 °C, whilst also subjecting them to 85% relative humidity. Intermediate visual and electroluminescence inspections revealed mechanical failure in air-filled modules due to edge seal flattening and cell breakage. Whilst after the full 30 humidity freeze cycles the relative degradation in module efficiency in both PDMS and glycerol encapsulated modules (both 5.2%) are comparable to that of an air-filled module (5.5%) but worse than that of EVA (3.9%), whilst the module encapsulated with MPG shows the lowest degradation (2.8%). These results highlight the potential of MPG as a stable encapsulant and underscore the importance of redesigning the liquid injection method for reliability of the polyisobutene edge seal


The humidity freeze accelerated ageing subjects the modules to extremely low and high temperatures of -40 °C and 85 °C, whilst also subjecting them to 85% relative humidity. Intermediate visual and electroluminescence inspections revealed mechanical failure in air-filled modules due to edge seal flattening and cell breakage. Whilst the full 30 humidity freeze cycles show that relative degradation in module efficiency in PDMS and glycerol encapsulated modules (both 5.2%) are comparable to those of an air-filled module (5.5%) but worse than that of EVA (3.9%), whilst the module encapsulated with MPG shows the lowest degradation (2.8%). These results highlight the potential of MPG as a stable encapsulant and underscore the importance of redesigning the liquid injection method for reliability of the polyisobutene edge seal.