External Thermalization of Carriers With Luminescent Down Shifting for Lower Operating Solar Cell Temperature

Luminescent down shifting (LDS) is a light management technique that can be used to exploit more efficiently the short-wavelength photons of the solar spectrum, to which most solar cell technologies exhibit relatively poor response. In practice, LDS is a thermalization process of carriers that takes place outside the solar cell itself and, therefore, has the potential of reducing its operating temperature, and thus increasing its electrical power output in field applications. In this study, we use ray-tracing and an electric-like thermal circuit to calculate the temperature variation of both multicrystalline silicon (mc-Si) and cadmium telluride (CdTe) photovoltaic modules containing LDS layers. We find that the dominant factors for the final operating cell temperature under the modified spectrum are reduced light reflection and parasitic absorption in the encapsulants. LDS, in practice, results in only a small variation compared with standard non-LDS modules, of up to +0.1 °C for the case of mc-Si and -0.6 °C for the CdTe. Although lowering operating cell temperature by means of LDS does not constitute in itself a strong reason for adopting the technology, this study paves the way for using optically active encapsulation layers with this purpose in mind.