| This thesis presents a new methodology for characterizing the gap defect states in intrinsic a-Si:H materials in the annealed and 1sun degraded steady states by combining results on thin films with those on metal Schottky barrier cell structures. An improved gap state distribution, consisting of five gaussians to represent positively charged (D+, D+*), negatively charged (D−, D−*), as well as neutral dangling bond (D0) states, is successfully used to self-consistently analyze a wide range of cell characteristics in Schottky barrier cells with different thickness. Using AMPS (Analysis of Microelectronic and Photonic Structures) to model the Schottky barrier cell structures and SAM (subgap absorption model) to model the concurrent results on thin films, “operational” parameters are obtained for the energy, density, and carrier capture cross-sections of the various gap states. This is achieved by “reiterative” fitting of a wide range of characteristics, including forward I-V, light I-V, and quantum efficiency, on Schottky barrier cell structures having thickness from 0.2 to 1.1μm. These “operational” parameters are also applied to the analysis of the characteristics of p(a-SiC:H)-i(a-Si:H)-n(μc-Si:H) solar cell structures. Excellent agreement is obtained between results of the simulations and the experimental results of cells having high quality p/i interface regions without introducing arbitrary p/i interface regions as has been done in the past.; Studies on the light induced changes with different light intensities and different temperatures were also carried out on the Schottky barrier cells in order to obtain new insights into the nature of the light induced defects in the intrinsic bulk materials. Results of these studies further confirm the presence of more than one type of defect in the a-Si:H materials and indicate competing mechanisms between generation and annealing in all these states, rather than just D0, in obtaining the degraded steady state. Furthermore, the large, rapid 1sun light induced changes in the thin films are also observed in far forward bias currents in the Schottky barrier cells and have been correlated with the creation of light induced defects in their bulk region and not at the n/i or metal/i interfaces. |
