Optical and photoconductive properties of discharge-produced amorphous silicon

Abstract

Optical and photoconductive properties of discharge-produced amorphous silicon (a-Si) of the type used in efficient thin-film solar cells have been studied as a function of a wide range of deposition conditions. The optical absorption, optical band gap, photoconductivity, hydrogen content, and the characteristics of the Si-H vibrational mode in a-Si were determined. Both substrate temperature in the range ∼200–400 °C and the type of discharge used are found to be important factors in determining the measured optical and photoconductive properties of a-Si. For films produced at substrate temperatures near 200 °C, dihydride bonding occurs, and the optical band gap is about 1.7 eV. As the substrate temerature increases, monohydride bonding is favored, the optical band gap decreases, the optical absorption increases, and the photoconductive properties improve. These properties are, in part, associated with the presence of bonded hydrogen. For substrate temperatures between 300 and 400 °C, the photoconductive properties are not strongly affected by changes in the substrate temperature, but are strongly influenced by the deposition technique. The Si-H bond is shown to be stable to thermal treatments at or below the deposition temperature. This is critical for the stability of a-Si properties in the fabrication of solar cells and other devices at elevated temperatures.

Stability of Polymer Solar Cells

“…The authors found the corresponding CN 18 O image for the 18 O 2 exposed device to be equivalent with the 18 O image, which they took as evidence that it was (at least) the nitrogen part of the molecule ( Figure 13) that was photo-oxidized. The phenomenon shown in Figure 15 has been mentioned by Norrman et al [203][204][205][206] in several of publications where TOF-SIMS was used in combination with isotopically labeled atmospheres.…”

Energy dependence of the carrier mobility-lifetime product in hydrogenated amorphous silicon

“…The gap electrode geometry yields the ambipolar secondary photoconductivity. [3][4][5][6][7][8] In this measurement, gap electrodes do not block either carrier. Hence, the photoconductivity is due to the secondary photocurrent of both carriers and will be denoted by SSPC (ie., §econdary electron and §econdary hole Qhoto.Qonductivity).…”

Structural origins of intrinsic stress in amorphous silicon thin films

“…2 allows the determination of the atomic and mass density of the film. 8,[10][11][12] From here, the total hydrogen content, as well as the content of hydrogen bonded as Si-H (2000 cm -1 ) and in nanovoid (2090 cm -1 ) configurations can be obtained, the latter providing us with a quantitative measurement of film porosity. For simplicity, and due to their inherent similarity, we will use the term "hydrogen void concentration" to refer to both the atomic concentration of hydrogen in the high stretching mode configuration and the film porosity.…”