Hydrogel-Based Passive Cooling for Photovoltaic Systems: Mechanisms, Materials Design, and Performance Benchmarking

The power conversion efficiency of photovoltaic (PV) solar cells deteriorates markedly as operating temperatures rise above ambient, with silicon-based modules losing roughly 0.45% of efficiency per degree Celsius of excess heat. Conventional active cooling—water spraying, forced-air circulation— restores performance but consumes electricity and complicates installation. Passive evaporative cooling by hydrogels presents a zero-energy alternative that exploits the large latent heat of water vaporization (approximately 2450 J g⁻¹). This seminar paper synthesizes three recent studies that collectively advance the design, characterization, and deployment of hydrogel-based cooling systems for photovoltaics. Li et al. (Small, 2026) engineered a spectrally tailored, Janus-structured, LiCl- embedded two-layer membrane capable of simultaneous evaporative and radiative cooling from the front surface of both rigid silicon and flexible polymer solar cells, achieving a maximum efficiency improvement of 21.3% under outdoor conditions. Tadano et al. (Journal of Applied Polymer Science, 2024) demonstrated that macroporous polyacrylamide hydrogels fabricated by slow-rate freeze casting sustain stable, capillary-fed evaporative cooling even under airflow, reducing target temperatures by up to 72°C relative to the uncooled baseline. Lapsirivatkul et al. (Advanced Materials Technologies, 2025) showed that semi-interpenetrating polymer networks of poly(N-isopropylacrylamide) and polyacrylamide combine a swelling ratio of 30 with a rapid water release rate and a specific cooling power of 1.86 W g⁻¹, cooling silicon PV cells by 23°C while requiring only 5.1 kg m⁻² of material— approximately 90% less than conventional phase-change materials. Together, these works reveal how hydrogel architecture, porosity, hygroscopic salt loading, optical properties, and thermoresponsive phase transitions can be co-engineered to maximize photovoltaic performance under realistic operating conditions.