Photoemission studies on undoped SnO₂ buffer layers for CdTe thin film solar cells

Intermediate highly resistive layers of transparent undoped oxide materials are known to improve the characteristics of thin film solar cells, as observed for SnO₂ used in CdTe solar cells with reduced CdS layer thickness. Comparative photoemission spectroscopy studies were carried out on commercial undoped and fluorine doped SnO₂ prepared by spray-pyrolysis, revealing that the Fermi level positions of the surfaces of both commercial samples are identical and degenerate. The commercial SnO₂ was compared to SnO₂ prepared by RF magnetron sputtering under different oxidation conditions. The sputtered samples were only weakly n-doped. Additionally, the influence of different sample treatments was investigated.