Indoor Photovoltaics for the Internet-of-Things - A Comparison of State-of-the-Art Devices from Different Photovoltaic Technologies

Photovoltaics (PV) is an attractive candidate for powering the rapidly growing market of smart devices in the Internet-of-Things (IoT) such as sensors, actuators, and wearables. Using solar cells and rechargeable batteries to power IoT devices avoids the expensive replacement of disposable batteries and reduces the environmental impact. IoT devices are often operated indoors under artificial light, which differs from (outdoor) sunlight as it is a much narrower, mainly visible spectrum with typically a factor of 500-1000 lower intensity. In this work, the performances of state-of-the-art devices of eight different PV technologies (amorphous and crystalline silicon, copper indium gallium selenide, cadmium telluride, III-V, organic, dye-sensitized, and perovskite) are compared under identical indoor illumination conditions. Their performance under low illuminances between 100 and 1000 lx is analyzed, and the crucial importance of sufficiently large parallel resistance is highlighted. Absorber materials with larger band gaps show less thermalization losses and thus reach higher power conversion efficiencies, in agreement with theoretical expectations. The best device, a gallium indium phosphide solar cell, with a band gap of 1.89 eV shows a record efficiency of 39.9% under 500 lx cold white LED light.