Optimal bandgap of a single-junction photovoltaic cell for the mobile Internet-of-Things.

The procedure for determining the maximum power of a single-junction photovoltaic cell operating in various types of lighting is presented. This is a key issue for photovoltaics powering the mobile Internet-of-Things (IoT). The simulations performed are based on the detailed balance principle, without any of the simplifying assumptions included in the Shockley-Queisser model. Optimal energy bandgap for diffuse solar light was found to be 1.64 eV with a cutoff generated power of 37.3 W/m. For the LED lighting considered in this work, the optimal energy bandgap and maximum power limit are 1.86 eV, 1.63 W/m, and 1.79 eV, 1.51 W/m for cool and warm lighting, respectively, at 900 lux. Considering that the maximum power limit of diffuse solar radiation is much higher than the limit for LED lighting, we concluded that 1.64 eV is the optimal bandgap for most mobile IoT devices operating outdoors all or almost all the time.