Lithium-based water-absorbent hydrogel with a high solar cell cooling flux

The lifetime and photovoltaic conversion efficiency of the solar cell will decline as the temperature rises. Herein, a versatile hydrogel allowing atmospheric water harvesting and evaporative cooling is introduced to passively reduce the working temperature of the solar cell. As a flexible substrate, the lithium-rich and highly absorbent polyacrylamide hydrogel is employed to satisfy these specifications. Preferentially, the water-saturated hydrogel, which is bonded to the backside of the solar cell, collects the waste heat produced by the cell and dissipates it into the atmosphere by water evaporation. Importantly, the hydrogel naturally gathers atmospheric vapor at night or on overcast days to revive its cooling ability. This configuration endows the PV cell with a cooling flux of up to 529 W m−2 and thus reduces the working temperature of a polycrystalline silicon cell by 26 °C at 1 sun (=1 kW m−2) illumination. More importantly, the hydrogel arrangement supports 6.2 % and 17 % improvements in average open-circuit and maximum power output (or photovoltaic efficiency), respectively. This is devoid of limits on access to liquid water resources, making it a potential option for efficient and sustainable solar cell power generation.