Abstract
Research on improved amorphous silicon-based devices has focused on materials prepared at high temperatures and/or those grown under very reactive conditions. The use of these conditions for device applications requires the development of more robust transparent conductive oxide (TCO) substrates. A thin (<10 nm) ZnO coating on a SnOx-coated glass substrate could withstand RF (13.56 MHz) and very high frequency (VHF: 144 MHz) hydrogen plasma treatments; however, the TCO was strongly reduced by a higher density, higher energy electron cyclotron resonance (ECR) hydrogen plasma or a higher temperature. Ga-doped ZnO (GZO) TCO substrates exhibited greater resistance to hydrogen plasma induced reduction. RF magnetron sputter deposited crystalline GZO thin films were deposited and optimized at temperatures higher than 150°C on glass substrates. The electron mobility and the Ga doping efficiency were improved with increasing GZO deposition temperature. The performance of a-Si:H solar cells fabricated under standard conditions (∼220°C) on these GZO substrates increased with increased GZO deposition temperature. The performance of a-Si:H solar cells prepared under more reactive and/or at higher deposition temperatures on 250°C deposited GZO was also examined. Both high temperature (280°C)-deposited narrow-bandgap a-Si:H(Ar) and ECR hydrogen plasma deposited a-Si:H(Cl) based solar cells were significantly improved using high temperature deposited GZO substrates.