Approaching high efficiency wide range silicon solar cells

Photovoltaic micro energy harvesting for self-sufficient sensor system applications is a promising new market for silicon photovoltaics. Therefore, silicon solar cells need to work under weak light conditions both outdoors, e.g. in the forest, or indoors. Hence, the spectral distribution of the given conditions differs as well with the application. We present a new investigation of real conditions and a first evaluation for a frequently used office. Even during winter the contribution of the artificial light sources does not exceed 35%. The spectrum is mainly determined by sun light. In order to proof the feasibility of solar cells for micro energy harvesting simulations of the efficiency limits for different spectra and intensities were made. The simulation of the theoretical efficiency limits show that silicon, which is best suited for AM1.5, can achieve even higher efficiencies for artificial light sources. Concerning the technological feasibility, PC1D simulation show that a PERC structure can be optimized resulting in efficiencies of 20% at an intensity of 1 sun and still 14% at an intensity of 1/1000 sun. The efficiencies even rise for artificial spectra of energy saving lamps, halogen bulbs or LEDs.