The role of plasma induced substrate heating during high rate deposition of microcrystalline silicon solar cells

A 13.56 MHz parallel plate hydrogen-diluted silane plasma, operated at high pressure and high power, was used to deposit microcrystalline silicon solar cells with efficiencies of 6-9% at high deposition rates of 0.4-1.2 nm/s. In this regime new challenges arise regarding temperature control, since the high plasma power causes the substrate to heat up significantly during film deposition. We investigated this effect of plasma-induced substrate heating experimentally by means of pyrometric substrate temperature measurements and spectroscopic gas temperature measurements. The substrate temperature was observed to increase by up to 100 K during film deposition, depending on power density and deposition time. Performance of deposited solar cells decreased whenever the plasma induced heating caused a drift outside the ideal temperature window, of around 475 K (similar to 206 degrees C). Further analysis related this decrease in performance to the substrate temperature's influence on film crystallinity and open circuit voltage. (c) 2005 Elsevier B.V. All rights reserved.