Degradation Behavior of a-Si:H Pin Solar Cells With Intentionally O-Contaminated i-Layers

The discussion about the influence of oxygen on the degradation be-havior of a-Si:H pin solar cells is now as before controversial. Therefore, we prepared a-Si:H pin solar cells having different amounts of O contami-nation in the i-layer by adding O2 gas to the silane gas during the glow-discharge deposition of the i-layer. The admixture of O2 gas was in the 0 ppm to 1000 ppm range resulting in an O concentration in the i-layer of 1.10190/cm3 to 3.1020 0/cm3 determined by SIMS measurements. Then we inves-tigated the long-term degradation behavior of these cells, exposing them for about 270 h to white light of 100 mW/cm2 intensity. During the first 20 h the cell efficiencies dropped relatively fast to about 80 % of the initial value and then more slowly to about 60 % after 270 h. The degradation of the cells may be slightly different during the first 20 h, but this has nothing to do with the O concentration. The normalized efficiency values meet all at the 60 % level after the long-term light exposure for 270 h. We there-fore conclude that the degradation behavior of pin a-Si:H solar cells after long-term exposure is not dependent on the O concentration in the range investigated. At O concentrations higher than about 5.1020 cm−3, the den-sity of states increases rapidly and the electrical properties of the solar cells deteriorate, making it difficult to clarify the true influence of oxygen on the degradation behavior.