Effect of forming gas annealing on hydrogen content and surface morphology of titanium oxide coated crystalline silicon heterocontacts

Crystalline silicon (c-Si) heterojunction solar cells using carrier-selective contacts have drawn considerable attention due to their high power conversion efficiency with a simple fabrication process. Titanium oxide (TiOx) is one of the most promising materials that can provide excellent surface passivation as well as carrier-selective transport. In this study, the authors fabricate the TiOx/SiOx/c-Si heterocontacts by atomic layer deposition (ALD) and investigate the effect of the forming gas annealing (FGA) on hydrogen content and surface morphology by utilizing nuclear reaction analysis (NRA) and atomic force microscope (AFM) measurements, respectively. The highest effective carrier lifetime (tau(eff)) of 891 mu s is realized for TiOx/SiOx/c-Si heterocontacts after FGA at 400 degrees C for 3 min, indicating that high surface passivation performance is obtained. NRA clarifies that the hydrogen content in the TiOx/SiOx/c-Si heterocontacts decreases with increasing FGA temperature and duration. With increasing FGA temperature and duration, also the surfaces of the TiOx/SiOx/c-Si heterocontacts are roughened, which means enhanced crystallization of the TiOx/SiOx/c-Si heterocontacts. From the NRA and AFM analyses, the authors conclude that there is a trade-off relationship between the hydrogen content in the TiOx/SiOx/c-Si heterocontacts and the crystallization of the TiOx layers.