Direct determination of total hemispherical emittance of perovskite and silicon solar cells

The performance and lifetime of a solar cell is sensitive to its operating temperature. In applications such as building-integrated photovoltaics, an accurate knowledge of the total hemispherical emittance as a function of temperature is required to calculate total radiative heat transfer and hence solar cell operating temperature. Here, we report a direct and absolute calorimetric method based on Stefan-Boltzmann's law for determining total hemispherical emittance of a surface. This method is applied to measure front and rear total hemispherical emittance of silicon and perovskite solar cells with and without encapsulation. Results show that the encapsulation material and the type of rear electrode strongly influence the emittance of the cell. Additionally, total hemispherical emittance values of solar cells determined in this work are considerably lower than spectral emittance values previously measured. These findings demonstrate the importance of front and rear materials selection in the optimization of radiative cooling for efficiency and lifetime.