High-rate deposition of microcrystalline silicon p-i-n solar cells in the high pressure depletion regime

Hydrogenated microcryst. silicon films (micro c-Si:H) deposited at high deposition rates (.apprx.2 nm/s) by means of the very-high-frequency deposition technique in the high pressure depletion regime have been integrated into single junction p-i-n solar cells. It is demonstrated that micro c-Si:H solar cells can be optimized using a twofold approach. First the bulk properties, deposited under steady-state plasma conditions, are optimized by monitoring the presence of cryst. grain boundaries in micro c-Si:H. These hydrogenated cryst. grain boundaries can easily be detected via the cryst. surface hydrides contribution to the narrow high stretching modes by IR transmission spectroscopy. The cryst. grain boundaries suffer from post-deposition oxidn. which results in a reduced red response of the solar cell. The absence of these cryst. surfaces in an as-deposited micro c-Si:H matrix reflects the device grade microcryst. bulk material. Second, the prevention of silane back-diffusion from the background during the initial growth is a necessity to deposit a uniform micro c-Si:H phase over the entire film thickness. The initial growth is optimized while preserving the optimized bulk properties deposited under steady-state conditions, using initial profiling of plasma parameters such as the silane flow and the very-high-frequency power d. Solar cell devices with efficiency of 8.0% at a micro c-Si:H deposition rate of 2.0 nm/s are obtained using the presented approach