Photovoltaic energy harvesting for smart sensor systems

Commercial photovoltaic cells used in energy harvesting applications suffer from low power conversion efficiencies at low light intensities. Typical efficiencies are in the range of 2 to 5% at 100 Lux. This is because the cells are typically optimized and specified with respect to the AM 1.5 sun spectrum at 1000 W/m2 light intensity, which is far away from the required operating range. This paper infers design rules for photovoltaic cells with special attention to the low intensity range. It discusses the major parameters for the optimization of photovoltaic cell for different material classes like crystalline silicon, amorphous silicon and III-V materials. Measurement results for an optimized silicon cell with more than 15% efficiency at 100 Lux are presented.