Importance of charge defects in a-Si:H materials and solar cell structures

Detailed results and their analysis are presented for establishing the types and densities of gap states in a-Si:H, deposited from silane diluted with hydrogen, in the annealed and the degraded stabilized states. For ~1 μm thick films the dependence of both the electron mobility-lifetime products (μτ) and subgap absorption measured with the dual beam photoconductivity (DBP) method over wide generation rates is self consistently fitted using an improved subgap absorption model (SAM). The self-consistent analysis of all the results could be carried out only by including donor-like D⁺, D^o and acceptor-like D^- defect states. “Operational” parameters of these states were derived for a three-gaussian distribution using AMPS with virtually identical gap state parameters. Excellent fits were then obtained for the far forward I-V characteristics of corresponding Schottky barrier cell structures in both the annealed and stabilised degraded states after changing by more than three to four orders of magnitude