Amorphous/crystalline silicon heterojunctions under intensive illumination

We study amorphous/crystalline silicon heterojunctions (Si HJ) in both p-type and n-type c-Si solar cells under high level of photon injection using concentrated light up to 55 suns. The performance of the cells under intensive light is similar to other types of crystalline Si solar cells. The open circuit voltage (V_oc) increases logarithmically with light intensity for both n-type and p-type base cells and best 760 mV at 48 suns. The best cell efficiency peaks around 10 suns at 19.6% on an untextured p-type Si HJ cell. It represents an 11% increase of the efficiency relative to the one at 1 sun. The decrease of cell efficiency at a higher light intensity is mainly due to the decrease of fill factor (FF). We also found that the FF decreases much quickly in the cell with an n-type wafer compared to a p-type wafer. After more experiments with controlled front finger space, wafer bulk resistivity, and the area of the cells, we conclude that there is a difference in carrier collection for the heterojunction emitters of the n-type and of the p-type c-Si solar cells under intensive illumination.