Oxygen and nitrogen impurities in microcrystalline silicon deposited under optimized conditions: Influence on material properties and solar cell performance

Abstract

The influence of oxygen and nitrogen impurities on the performance of thin-film solar cells based on microcrystalline silicon (mu c-Si:H) has been systematically investigated. Single mu c-Si:H layers and complete mu c-Si:H solar cells have been prepared with intentional contamination by admitting oxygen and/or nitrogen during the deposition process. The conversion efficiency of similar to 1.2 mu m thick mu c-Si: H solar cells is deteriorated if the oxygen content in absorber layers exceeds the range from 1.2 x 10(19) to 2 x 10(19) cm(-3); in the case of nitrogen contamination the critical impurity level is lower ([N](critical)=6 x 10(18)-8 x 10(18) cm(-3)). It was revealed that both oxygen and nitrogen impurities thereby modify structural and electrical properties of mu c-Si:H films. It was observed that the both contaminant types act as donors. Efficiency losses due to oxygen or nitrogen impurities are attributed to fill factor decreases and to a reduced external quantum efficiency at wavelengths of >500 nm. In the case of an air leak during the mu c-Si:H deposition process, the cell performance drops at an air leak fraction from 140 to 200 ppm compared to the total gas flow during i-layer deposition. It is demonstrated that oxygen and nitrogen impurities close to the p/i-interface have a stronger effect on the cell performance compared to impurities close to the n/i-interface. Moreover, thick mu c-Si:H solar cells are found to be more impurity-sensitive than thinner cells

Microcrystalline silicon films and solar cells deposited at high rate by Matrix Distributed Electron Cyclotron Resonance (MDECR) plasma

“…and thus, these values are now below the corresponding critical thresholds of deterioration of cell performance of 1.2 to 2 × 10 19 cm −3 and 6 to 8 × 10 18 cm −3 respectively reported in [9]. Additionally, C C = 1.4 × 10 19 cm −3 , and C F = 4.2 × 10 17 cm −3 , which is probably still too high for carbon but this cannot explain the very limited efficiencies of the cells.…”

Limitations of high pressure sputtering for amorphous silicon deposition

“…In the figure we can observe two bands at 647 cm ) modes. At 1050 cm −1 it is expected the Si-O related band [19], but for these samples it is almost negligible. The behavior of all these bands is in full agreement with the results of the composition and OES measurements.…”

Low temperature processed p‐type bottom gate microcrystalline silicon thin film transistors

“…Our best p-type BG TFTs exhibit a field effect mobility of ~ 1. channel by nitrogen, which can lead to an unintentional ntype doping the following layers (intrinsic and p-doped µc-Si) were deposited in a different reactor [10]. Moreover, as p-type channels TFTs are very sensitive to any residual gases, special attention was paid to outgas the reactor before µc-Si deposition.…”