THE SATURATION OF LIGHT-INDUCED DEFECTS IN HYDROGENATED AMORPHOUS-SILICON

The saturation light-induced defect density, N(sat), of a-Si:H obtained by sufficiently high photon flux with a Kr+ laser is introduced. N(sat) is insensitive to light intensity and to temperature, and is therefore independent of spatial or temporal variations of the light-soaking conditions. In addition, N(sat) is correlated with the defect growth rate at typical sunlight intensity, and the defect growth rate from N(sat) can be estimated. Therefore, N(sat) is a robust criterion for the stability of a-Si:H. The entire light-soaking history of a material can be evaluated in a few hours, and feedback on stability can be provided quickly to the deposition laboratory. In electronic-grade samples obtained from many different laboratories and deposited by different techniques, N(sat) rises with the Tauc gap, E(Tauc), or E04 and with the total hydrogen concentration, c(H), but is not correlated with the initial defect density or the Urbach energy. The N(sat) values measured so far lie between 4 x 10(16) and 2 x 10(17) cm-3. It is demonstrated that the defect history inferred from N(sat) may be used to predict the degradation of solar cells. The temperature dependence of N(sat) can be explained by a limited number of defect sites coupled with an annealing process within the defect pool model.