Spectrally Engineered Coatings for Steering the Solar Photons

Abstract

The spectral properties of radiative cooling (RC) and photovoltaic (PV) govern their capacity to utilize solar photons at distinct energy levels. However, spectral mismatches with the solar spectrum result in significant inefficiencies: non-photovoltaic heat losses in PV panels and wasted energy from reflected solar radiation in RC systems. To address this, a photoluminescent RC coating with spectrally selective reflectivity is developed to be integrated it with bifacial photovoltaic (biPV) panels. The high reflectivity of the RC coating directs photons to the rear side of the PV panels, while its spectral selectivity optimizes the energy distribution of photons reaching the rear side, resulting in a 32% increase in the overall power output of the bifacial PV system. Additionally, the incorporation of photoluminescent materials enables the conversion of absorbed photons into luminescence rather than heat by suppressing non-radiative transitions. This reduces effective solar absorption by 14% and enhances radiative cooling performance. Simulated urban rooftop deployment demonstrates that this dual-harvesting system meet ≈18.1% of Hong Kong's annual electricity demand, offering a scalable pathway toward carbon-neutral cities.