Intrinsic and light induced gap states in a-Si:H materials and solar cells—effects of microstructure

Abstract

The effects of microstructure on the gap states of hydrogen diluted and undiluted hydrogenated amorphous silicon (a-Si:H) thin film materials and their solar cells have been investigated. In characterizing the films the commonly used methodology of relating just the magnitudes of photocurrents and subgap absorption, α(E), was expanded to take into account states other than those due to dangling bond defects. The electron mobility-lifetime products were characterized as a function of carrier generation rates and analysis was carried out of the entire α(E) spectra and their evolution with light induced degradation. Two distinctly different defect states at 1.0 and 1.2 eV from the conduction band and their contributions to carrier recombination were identified and their respective evolution under 1 sun illumination characterized. Direct correlations were obtained between the recombination in thin films with that of corresponding solar cells. The effects of the difference in microstructure on the changes in these two gap states in films and solar cells were also identified It is found that improved stability of protocrystalline Si:H can in part be attributed to the reduction of the 1.2 eV defects. It is also shown that ignoring the presence of multiple defects leads to erroneous conclusions being drawn about the stability of a-Si:H and SWE.

Effect of light soaking on CPM absorption spectra in silicon films with mixed amorphous‐nanocrystalline structure

“…For these films α rel (1.0 eV) decreases with increasing R H . This result is consistent with CPM absorption [7] and EPR [2] data on defect concentration in amorphous silicon films with embedded nanocrystallites. These amorphous silicon films are referred to as protocrystalline silicon films.…”

“…Microstructure of silicon films can be controlled from highly amorphous to predominantly crystalline by varying the dilution of silane source gas with hydrogen during the rf plasma enhanced chemical vapor deposition [7]. In this work we report a systematic study of hydrogenated silicon films prepared for different hydrogen dilutions.…”

Electrical and optical properties of boron‐doped nanocrystalline silicon films deposited by PECVD

“…It has been reported 17, 18 that a lower density of interface states results in higher σ . A faster deposition rate is beneficial to the large‐scale production.…”

Defect-state engineering in a-Si:H: An effective tool for studying processes during light-induced degradation

“…The contributions of the individual D h , D z , and D e components to overall EDOS determined from the fitting procedure were estimated via the decomposition of the EDOS into three Gaussian distributions. This decomposition stems from the experimental observation of three groups of defects reported also by other authors [10][11][12][13]. Each Gaussian distribution was determined by three parameters: the position of the peak, the height, and the standard deviation of the Gaussian distribution.…”