Designing, fabricating and testing multi-junction silicon solar cells

Photovoltaic research and technology have grown exponentially in recent years due to the continuing and increasing global demand for energy. However, to be economical for global production and utilization, the efficiency of solar cells must increase without escalating manufacturing costs. Because of the abundance of silicon and vast knowledge obtained from silicon study, exhaustive exploitation of silicon-based solar cell design is vital to meet both criteria. Positive thermal control and improved photon recycling are two methods to increase solar cell efficiency. A recently developed hybrid multi-junction silicon (HMJ-Si) solar cell architecture was designed to positively manage these two factors, as well as the common resulting photonic interference pattern generated from the electrical contact gratings. Because of the integrated air gap between two stacked silicon substrates, this sandwiched-cavity imparted a 1.70C differential temperature. The top and bottom substrates were electrically connected in parallel via a copper o-ring with a thickness of 385μm which was the optimal, calculated air gap distance for photon propagation wavelengths of 800nm-1100nm. The HMJ-Si solar cell was tested using a solar simulator with an air mass 1.5 full spectrum sunlight output and a class II pyranometer with a spectral response of 310nm-2800nm. The HMJ-Si solar cell demonstrated photovoltaic efficiency of 8-10%.