Design of radiative cooler based on porous TiO₂ for improving solar cells' performance

It is widely known that the conversion efficiency and lifetime of solar cell modules decrease with higher operating temperatures. To maximize both efficiency and reliability, solar cell modules benefit greatly from the use of daytime passive radiative cooling techniques. In this study, we introduce a simple, low-cost, double-layer coating based on porous TiO₂ as a daytime passive radiative cooling system to achieve sub-ambient operating temperatures in a solar cell module. The top and bottom layers of the implemented design are porous TiO₂ and BK7 (glass), respectively. This solar cell/radiative cooling hybrid design is capable of achieving both high solar absorption in the photovoltaic conversion band 0.3-1.1 µm and high emissivity over 0.96 in the atmospheric transparency window 8-13 µm, while rejecting parasitic solar absorption. At 800W/m² solar heating power, we found that adding the proposed cooling design on top of mono-crystalline silicon (m-Si), the solar cell panel lowered its operating temperature by 18.04°C, leading to a relative (effective) efficiency advantage of 21.56%. Additionally, at steady-state temperature (325 K), the power conversion efficiency of our radiative-cooler-coated m-Si solar cell is estimated to reach 20.46%, in contrast to 16.83% for an uncoated silicon solar cell. When compared with an uncoated silicon solar cell, optoelectronic simulations of our coated silicon solar cell show a short-circuit current density J as high as 5.07mA/cm², and the open circuit voltage V increased from 771.78 to 776.3 mV.