Spectrally and spatially resolved electroluminescence emission of crystalline silicon solar cells is interpreted in terms of two electro-optical reciprocity relations. The first relation links the photovoltaic quantum efficiency to the electroluminescence spectrum. Both methods contain information on recombination and the optical pathlength of the incident light, simultaneously. From the electroluminescence spectrum, we derive the pathlength enhancement factor of textured and untextured crystalline silicon solar cells. Further, we use local quantum efficiency measurements to quantitatively explain light induced current as well as panchromatic electroluminescence images. A second reciprocity relation connects open circuit voltage of a solar cell with the light emitting diode quantum efficiency of the same device. For a given quality of light trapping and a given open circuit voltage, we predict the attainable LED quantum efficiency and verify our results experimentally.
This device design approach combines sputter-deposited TiO2 antireflection layer (ARL) and plasma-enhanced chemical vapor deposition-grown SiOx intermediate-reflector layer (IRL) in superstrate a-Si∕μc-Si thin film solar cell. The loss of current from either the component cells with individual application of ARL and IRL has been recovered with their combined application. With both ARL and IRL in a-Si∕μc-Si cell, (a) the top cell current and (b) the sum of top and bottom cell current increases. An initial efficiency of 11.8% [Voc=1.42V, FF=0.74, Jsc (top)=11.5mAcm−2, Jsc (bottom)=11.2mAcm−2] is achieved from such an a-Si∕μc-Si cell with a total Si layer thickness less than 2μm.
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