A Lightweight Hydrogel System for Passive Cooling of Solar Cells

Abstract The power conversion efficiency (PCE) of photovoltaics (PVs) or solar cells is significantly affected by the temperature. Under 1‐sun solar irradiance, the PV temperature can reach up to 65–70 °C; consequently, the PCE and power output can be reduced by as much as 18%. Herein, highly efficient PV passive cooling based on thermoresponsive poly( N ‐isopropylacrylamide) (PNIPAM) semi‐interpenetrating polymer networks (semi‐IPNs) containing poly(vinyl alcohol) (PVA), poly(ethylene glycol) (PEG), or polyacrylamide (PAM), is demonstrated. Crucially, the measurements of water release ratio and differential thermal analysis (DTA) reveal that the cooling performance of hydrogels not only depends on how much water they absorb but also on how fast they can release water. The DTA experiments allow the quantification of specific cooling power (SCP). The optimal composition of PNIPAM/PAM hydrogels with 15 wt.% PAM shows the largest swelling ratio of 30 and highest SCP of 1.86 W g ⁻¹ . Employed in the cooling application of silicon PV cells, a large temperature reduction of 23 °C is achieved (from 70 to 47 °C), resulting in a relative increase in PCE by 12.3%. Remarkably, only 5.1 kg m ⁻² of the hydrogels is required, 90% lower than what is typically required of phase change materials for passive PV cooling.