Radiative cooling technologies toward enhanced energy efficiency of solar cells: Materials, systems, and perspectives

Solar cells (SCs) convert sunlight directly into electricity via the photovoltaic (PV) effect, paving a fossil fuel-free way to meet the increasing demand for renewable sources. However, most solar radiation (~ 80%) is transformed into thermal parasites that heat solar panels, significantly degrading the efficiency and life span of SCs. Passive sky radiative cooling (RC), which cools terrestrial objects by dissipating excessive thermal emission into the ultracold (~ 3 K) space, appears as an emerging cooling technology and has attracted considerable attention. As SCs are predominantly engaged in PV conversion during daytime, the incorporation of RC technology enables temperature decrease, subsequently boosting solar-to-electricity efficiency. Besides, integrating RC into SCs allows night cold harvesting that could be employed for daytime thermal management, further improving energy efficiency. Therefore, integrating RC with SCs represents a promising, energy-free way towards enhanced energy efficiency. This review commences with the energy balance within SCs and fundamental principles of RC technologies, summarizes remarkable daytime RC materials for temperature reduction and efficiency improvement of SCs, continues with innovative PV systems that integrate nighttime RC technologies, and finally ends with challenges and perspectives towards enhanced energy efficiency in PV systems via passive RC technologies.