Transparent silicon solar cells: Design, fabrication, and analysis

Transparent silicon can lead to increased conversion efficiency in a multi-junction assembly by transmitting near and below band gap energy photons to a lower band gap solar cell. With semi-empirical calculations from Gray et.al. potential efficiency gain from a lower band gap solar cell can be 4.9% absolute under concentration. The present work analyzes a 4-wire tandem system consisting of mono-crystalline silicon and a material of lower band gap filtered by a dichroic mirror under concentration. Optimization focuses on the thickness of the silicon, the band gap of the lower solar cell, and different levels of light concentration. Silicon devices are fabricated, tested outdoors, and analyzed to develop improved structures which are closer to the design goal for this transparent silicon solar cell of 8.2%. Devices fabricated for this work have high transparency to below band gap light and efficiency of 6.1% at 50X when filtered by the dichroic mirror. This compares favorably to the previously reported 5.4% for a transparent silicon solar cell as reported by Barnett et. al..