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.