Contributions of D 0 and non-D 0 Gap States to the Kinetics of Light Induced Degradation of Amorphous Silicon under 1 su
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Contributions of D0 and non-D0 Gap States to the Kinetics of Light Induced Degradation of Amorphous Silicon under 1 sun Illumination J. Pearce, X. Niu, R. Koval, G. Ganguly1, D. Carlson1, R.W. Collins, and C.R. Wronski Center For Thin Film Devices, The Pennsylvania State University, University Park, PA, 16801 1 BP Solar, 3601 Lagrange Parkway, Toano, VA 23168 ABSTRACT Light induced changes to 1 sun degraded steady state (DSS) have been investigated on hydrogenated amorphous silicon (a-Si:H) p-i-n solar cells and corresponding films fabricated with and without hydrogen dilution of silane. Striking similarities are found for the degradation NLQHWLFVEHWZHHQWKHHOHFWURQPRELOLW\OLIHWLPH
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creation of non-D defects is also clearly indicated by the temperature dependence of the kinetics DQGWKHFKDQJHVLQWKHVKDSHRI ( ZLWKWKHUHVXOts suggesting the presence of more than one mechanism for the creation of light induced defects associated with the Staebler-Wronski effect (SWE). INTRODUCTION There is great interest in understanding the Staebler-Wronski effect (SWE) in high quality a-Si:H materials as well as in correlating it with the degradation in the corresponding solar cells. Protocrystalline materials and cells, fabricated with hydrogen dilution of silane, have been found to have not only improved stability but also degradation kinetics such as reaching the degraded steady state (DSS) at 25Û&LQOHVVWKDQKRXUVDVFRPSDUHGWRWKHKRXUVRU more for their undiluted counterparts [1,2,3]. The differences between such intrinsic materials offer the possibility of obtaining new insights into the nature of light induced defects and the mechanisms responsible for their creation. Such insights have been obtained by L. Yang [4] from results on solar cell recoveries after high intensity light induced degradation, where the differences in the annealing kinetics revealed the presence of “fast” and “slow” states and their dependence on the different microstructure in the materials. The presence of multiple light induced defects in a-Si:H has also been indicated by a variety of results on thin films. This includes the necessity to invoke such defects in self-consistent analysis of the changes in photoconductivity [5,6] as well as the great difficulties in explaining the annealing kinetics of light induced changes in terms of only dangling bond defects [7,8]. Recently, Koval et. al. [9] reported results on 1 sun light induced changes of protocrystalline Si:H films and Schottky barrier solar cell structures fabricated with hydrogen dilution which identified several inconsistencies with inter
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