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

A 13.56 MHz parallel plate hydrogen-dild. silane plasma, operated at high pressure and high power, was used to deposit microcryst. 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 temp. 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 exptl. by means of pyrometric substrate temp. measurements and spectroscopic gas temp. measurements. The substrate temp. was obsd. to increase by up to 100 K during film deposition, depending on power d. and deposition time. Performance of deposited solar cells decreased whenever the plasma induced heating caused a drift outside the ideal temp. window, of around 475 K (.apprx.200 °C). Further anal. related this decrease in performance to the substrate temp.'s influence on film crystallinity and open circuit voltage