Abstract
Thin-film hydrogenated amorphous silicon solar (alpha-Si: H) cells are known to have better temperature coefficients than crystalline silicon cells. To investigate whether a-Si: H cells that are optimized for standard conditions (STC) also have the highest energy yield, we measured the temperature and irradiance dependence of the maximum power output (P-mpp), the fill factor (FF), the short-circuit current density (J(sc)), and the open-circuit voltage (V-oc) for four series of cells fabricated with different deposition conditions. The parameters varied during plasma-enhanced chemical vapor deposition (PE-CVD) were the power and frequency of the PE-CVD generator, the hydrogen-to-silane dilution during deposition of the intrinsic absorber layer (i-layer), and the thicknesses of the alpha-Si: H i-layer and p-type hydrogenated amorphous silicon carbide layer. The results show that the temperature coefficient of the V-oc generally varies linearly with the V-oc value. The J(sc) increases linearly with temperature mainly due to temperature-induced bandgap reduction and reduced recombination. The FF temperature dependence is not linear and reaches a maximum at temperatures between 15 degrees C and 80 degrees C. Numerical simulations show that this behavior is due to a more positive space-charge induced by the photogenerated holes in the p-layer and to a recombination decrease with temperature. Due to the FF(T) behavior, the P-mpp (T) curves also have a maximum, but at a lower temperature. Moreover, for most series, the cells with the highest power output at STC also have the best energy yield. However, the P-mpp (T) curves of two cells with different i-layer thicknesses cross each other in the operating cell temperature range, indicating that the cell with the highest power output could, for instance, have a lower energy yield than the other cell. A simple energy-yield simulation for the light-soaked and annealed states shows that for Neuchatel (Switzerland) the best cell at STC also has the best energy yield. However, for a different climate or cell configuration, this may not be true. (C) 2016 AIP Publishing LLC.