Amorphous silicon solar cells with graded low-level doped i-layerscharacterised by bifacial measurements

Bifacial spectral response characterization of solar cells under near operating condition illumination is used in conjuncture with a novel bifacial DICE analysis to establish the collection efficiency as a function of i-layer position in p-i-n amorphous silicon solar cells. A significant portion of solar cell degradation can be explained in terms of electric field distortions which increase recombination losses. Unlike carrier lifetime reductions, the field distortions can be reduced. The numerical model is used to guide the intentional doping of the i-layer to counteract the field distortions caused by charged dangling bonds, and thus to optimize the electric field for the degraded state. Solar cells with graded low-level boron doping in the i-layer are analysed in detail. Increasing conversion efficiency during light-soaking, and enhanced stabilized n-side performance show the viability of the electric field optimization.