Silicon Concentrator Solar Cells: Fabrication, Characterization and Modeling for Future Improvements

Small size silicon concentrator solar cells have been developed showing good performance in low and medium concentration range. In this work we describe the fabrication technology, characterization and modeling of these cells. The cell conversion efficiency, Internal Quantum Efficiency (IQE), Open Circuit Voltage (VOC) and Short Circuit Current Density (JSC) were evaluated in the 1-200 Suns concentration range. The conversion efficiency is of 20.8% at 60 Suns and higher than 18.6% up to 200 Suns. The dependence of JSC on the concentration factor has been observed to be super-linear, with an 8% excess JSC at 200 Suns. Numerical simulations, calibrated and optimized to take into account the carrier recombination and mobility in high injection condition, match the experimental measurements and correctly predict the JSC super-linearity. This effect has been further investigated and explained by the enhancement of electric field in the base region, allowing an improvement of the minority carriers collection efficiency. Finally, numerical simulations, validated by the experimental measurements, were applied to optimize the cell design in terms of front metal finger pitch for different concentration levels.