Defect density and recombination lifetime in microcrystalline silicon absorbers of highly efficient thin-film solar cells determined by numerical device simulations

Abstract

The absorber layers of microcrystalline silicon thin-film solar cells with p-i-n structure deposited by plasma-enhanced chemical vapor deposition at 200 °C are characterized regarding the defect density and the recombination lifetime. The characterization is based on a comparison of experimentally determined solar cell characteristics with results from numerical device simulations. Evaluation of the dark reverse saturation current indicates a strong dependence of the recombination lifetime τ on the hydrogen dilution during the deposition. Close to the transition region to amorphous growth, where the highest solar cell efficiencies are observed, τ is maximum within the crystalline deposition regime and equals around 80 ns. The aspect of a spatially varying defect density within the absorber layer is also addressed by numerical simulations. The results from the analysis of the dark current are compared with electron spin resonance data determined on single layers, which allows conclusions to be drawn regarding the capture cross section of the dominant recombination site in microcrystalline silicon.

Influence of contact effect on the performance of microcrystalline silicon thin-film transistors

“…The determined defect density ͑3.5ϫ 10 16 cm −3 is in the range of the values obtained from the electron spin resonance and detailed device analysis. 15 This underlines that Eq. ͑5͒ can be applied to describe the subthreshold current of the c-Si: H TFTs.…”

Exploring dark current voltage characteristics of micromorph silicon tandem cells with computer simulations

“…At high forward voltages there is some consensus in that the dark J-V characteristic is controlled by series resistance when contacts do not hinder hole injection. 12,13,30 The measurement of the dark J-V at high forward voltages is particularly difficult in c-Si: H p-i-n devices due to the high current densities that could be achieved. Experimental setups are supplied with appropriate electronics to protect the equipment of excessive currents that might also damage the sample.…”

“…[12][13][14]30 Similarly, the two voltages V R and V E can be defined in the exponential region. At high forward voltages there is some consensus in that the dark J-V characteristic is controlled by series resistance when contacts do not hinder hole injection.…”

“…9,10 Dark J-V characteristics of single c-Si: H based p-i-n devices have also been studied in the literature but in less extent than in case of a-Si: H based devices. [11][12][13][14] The current at low forward voltages is a strong function of the silane ͓SiH 4 ͔ concentration ͑SC͒, defined as SC = ͓SiH 4 ͔ / ͓͑SiH 4 ͔ + ͓H 2 ͔͒, used in the gas phase to deposit in the intrinsic layer, the current being lower for higher values of SC. 12,13 The current at low forward voltages for these devices is always higher than in a-Si: H based p-i-n devices due to the lower band gap of c-Si: H ͑Refs.…”

Influence of low temperature thermal annealing on the performance of microcrystalline silicon thin-film transistors

“…Furthermore, the defect densities are similar to values estimated by electron spin resonance and detailed numerical analysis of microcrystalline silicon solar cells. 15,16 In the second case, the shift of the device threshold voltage is caused by a change in work function difference as a result of the change of energy diagram of the metal-oxide-semiconductor ͑MOS͒ structure formed by Al, SiO 2 , and c-Si: H. The thermal treatment leads to a modification of the Al/ SiO 2 interface, which affects the energy diagram of the MOS structure.…”