On the Role of Color Temperature and Color Rendering Index of White-Light LEDs on the Theoretical Efficiency Limit of Indoor Photovoltaics

Abstract

As the Internet of Things (IoT) continues to grow, the demand for sustainable indoor power sources is increasing. Indoor photovoltaics (IPVs), which are currently in development, present a renewable solution but must be designed to match specific light sources to maximize efficiency. While previous studies have emphasized the role of white-light LED correlated color temperature (CCT) in determining IPV efficiency and optimum bandgap energy, the role of color rendering index (CRI) remains less understood. In this study, we employ detailed-balance calculations to assess the theoretical maximum efficiency and optimal bandgap energies of IPVs under commercial white-light LED illumination varying in both CCT (2200 K to 6500 K) and CRI (70, 80, and 90). Our results confirm that lower CCTs yield higher efficiencies and lower optimal bandgaps; however, contrary to prior assumptions that CRI has negligible impact on IPV material choice and performance, we demonstrate that high-CRI LEDs necessitate the use of materials with significantly lower bandgap energies for optimum efficiency due to the shift towards red in the higher CRI irradiance spectra. We also evaluate the performance of various IPVs at fixed bandgaps, revealing that while optimal IPV performance is achieved with wide-bandgap materials under lower CRI lighting, mature technologies like silicon and CdTe benefit from high-CRI illumination. These findings underscore the need to consider both CCT and CRI in the design, evaluation, and choice of IPVs for indoor IoT applications.

Updated version with a focus on illuminance rather than irradiance; 12 pages excluding supplementary materials, 4 main figures; supplementary materials attached at the end of the manuscript