Investigating ZnO thin films as moisture barrier to enhance the long-term stability of solar cells under humid conditions

Enhancing the operational stability of solar cells under humid conditions remains a critical challenge for their large-scale commercialization. Here, we report RF-sputtered ZnO thin films (∼80 nm) as effective encapsulation layers for mitigating moisture-induced degradation. The films were deposited at different operating pressures to investigate the role of microstructural evolution on barrier performance. The ZnO-encapsulated solar cells exhibit significantly improved stability under accelerated ageing conditions of 50 °C and 80% relative humidity for 100 days, in contrast to rapid degradation observed in unencapsulated devices. Thin films deposited at higher pressure exhibit an improved and denser microstructure, along with a higher contact angle. This combination suppresses moisture diffusion, enabling the film to function effectively as an encapsulation layer. ZnO deposition as an encapsulant significantly improves device stability, increasing efficiency retention from 28% (bare cell) to 75% (H 0.04) after exposure. Overall, this work establishes sputtered ZnO thin films as a scalable and efficient encapsulation strategy, offering a promising route toward improving the environmental durability and lifetime of solar cell technologies.