Metal-halide perovskites (MHPs) have emerged as leading candidates for next-generation photovoltaics owing to their high efficiencies, low-cost processing, and compatibility with tandem architectures. However, their sensitivity to moisture, oxygen, heat, and ultraviolet radiation can induce performance losses through phase transitions, ion migration, and electrode corrosion. In addition, the intrinsic mechanical fragility of perovskite and charge-transport layers makes reliable encapsulation a critical challenge. Encapsulant materials must therefore provide effective environmental protection while remaining chemically, mechanically, and optically compatible with MHP devices and enabling low-temperature lamination.

To address this challenge, we evaluated several commercial photovoltaic encapsulants, including poly(ethylene-co-vinyl acetate) (EVA), polyolefin elastomers (POEs), thermoplastic polyolefins (TPOs) and polydimethyl siloxane (PDMS) for application with MHP solar cells and modules. The materials were first characterized in their unlaminated state through water vapor transmission rate (WVTR), dynamic moving die rheometer (D-MDR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) measurements. These properties were used to optimize lamination conditions prior to encapsulation of glass/glass laminates containing small-area single-junction (SJ) and perovskite/silicon (MHP/c-Si) tandem solar cells.

Post-lamination characterization revealed that residual crosslinkers remained present in all crosslinking encapsulants (EVA, POE) at a relatively low lamination temperatures (135°C) required to avoid damage to MHPs, even after curing times were extended beyond 3 times the standard duration. Reliability was then assessed through indoor accelerated aging - damp heat (85 °C / 85% relative humidity), thermal cycling (−40 to 80 °C), and light and temperature exposure (2 Suns at 70°C) - as well as outdoor monitoring under maximum power point tracking in Neuchâtel, Switzerland.

Two major incompatibility mechanisms were identified: first, a UV-blocking POE formulation reacted chemically with copper electrodes, causing yellow discoloration from copper oxide formation - observed under both indoor and outdoor conditions. Second, mechanical incompatibility between some encapsulants and the fragile MHP device stack led to interfacial delamination. Taken together, these results show that both encapsulant chemistry and mechanical properties play a decisive role in perovskite device durability.

Ongoing work focuses on clarifying the contributions of residual crosslinkers, acetic acid, and additives to device degradation, and to define practical selection criteria for MHP encapsulation.