High efficiency a-Si solar cells with ZnO films

In this study special importance is attached to the ZnO/p and n/ZnO interfaces. a-Si solar cells with a structure of glass/ZnO/delta doped p/buffer/i/n/ZnO/Ag/Al have been fabricated. By optimizing the grain size of the films along with their electrical and optical properties, a high conversion efficiency of 12.5% was obtained under AM-1.5 illumination. The collection efficiency of the cell at 700 nm reached 60%. Furthermore, effects of interface states represented by a barrier E_n at the n/metal contact were investigated. It was found that this barrier affected the performance of the cells, particularly when the n-layer became thin. Finally, to demonstrate the electrical role of the ZnO at back contact, p-i-n a-Si solar cells having thin n-layer combined with ZnO back contact were fabricated. It was surprisingly found that the performance of the cells with ZnO at back contact did not deteriorate though the thickness of the n-layer was reduced to 3 nm