Device physics of nanocrystalline silicon solar cells

We investigate the electronic properties of nanocrystalline silicon solar cells. It is shown that the material behaves very similarly to crystalline silicon but with mobility and minority carrier lifetimes being significantly lower than in c-Si. Mobility is shown to increase with grain size. Minority carrier lifetime was measured and shown to be inversely proportional to defect density. The recombination defects are shown to be approximately 0.4 eV below the conduction band. It is also shown that the fundamental optical absorption itself depends upon the grain size. We also show that a gradient of ppm levels of doping can improve the performance of solar cells by introducing a built infield. We also show that a post-deposition H anneal can reduce the defects and improve performance of devices made at higher temperatures.