Microcrystalline silicon solar cells prepared by 13.56 MHz PECVD : prerequisites for high quality material at high growth rates

Topic of this thesis was the development of thin film solar cells based on microcrystalline silicon prepared by 13.56 MHz PECVD (plasma-enhanced chemical vapor deposition) at high deposition rates. Comprehensive solar cell studies, which were accompanied by material studies, resulted in the identification of the most important prerequisites for high quality solar cells at high growth rates. During the development of solar cells in various pressure regimes, a high deposition pressure emerged as key parameter for good solar cell performance at high deposition rates. Plasma ignition at high deposition pressures (>10 Torr) was only possible at low electrode distances. Other important factors were a high total gas flow and a substrate temperature, which should not exceed $\sim$200 °C. As alternative approach deposition by pulsed plasma excitation was investigated. At deposition rates up to $\sim$5 $\mathring{A}$/s efficiencies comparable to continuous excitation were achieved, at higher rates the efficiency significantly decreased. In summary we succeeded in developing high quality solar cells at high deposition rates. Highlights were solar cells with 9.1, 9.0 and 8.9 % efficiency for deposition rates of 1, 3 and 4 $\mathring{A}$/s, respectively. At 9 $\mathring{A}$/s still a high efficiency of 7.9 % was achieved. Furthermore we gained an understanding of the prerequisites regarding the plasma properties to achieve high growth rates and high quality material