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The optimization of photovoltaic devices for versatile conditions is necessary to improve the energy capture for indoor applications, such as self sufficient sensors. However, the design rules of standard outdoor solar cells are not applicable for cells which are used indoors due to differing conditions from the standard testing conditions (STC). We will discuss the substantial influences on cell efficiencies and their impact on the design of photovoltaic cells with indoor applications. We show that in order to reduce losses due to recombination the influence of impurity recombination outweighs the Auger recombination. Therefore, good quality material and a reduction of the doping level are favorable. Thedo pant reduction implies an improvement of the saturation current density J_01and is realizable because the seriesresistance R_s has no influence on the efficiency at indoor intensities. The crucial parameter is the shunting resistance R_sh and it has to have a value of at least 50 k?cm2.