Hole drift mobility measurements in amorphous silicon-carbon alloys

Gu, Qing; Wang, Qi; Schiff, E. A.; Li, Yuan Min; Malone, Charles T.

doi:10.1063/1.358508

Cited by 48 publications

(45 citation statements)

References 9 publications

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“…1; L is the photocarrier displacement at the transit time ͑d / 2, if the entire sample is traversed͒, and E is the electric field ͑including an estimate of the effective, internal field͒. 7 The transit times were calculated using photocharge techniques 8,9 for the ratio L / E =7ϫ 10 −8 cm 2 / V. For reference, we show a multiple-trapping extrapolation of the hole drift mobility for one sample of a-Si: H; 10 it has not been feasible to directly measure D in a-Si: H for this value of L / E because of hole deep trapping by dangling bonds.…”

Section: Hole Drift-mobility Measurements In Microcrystalline Siliconmentioning

confidence: 99%

Hole drift-mobility measurements in microcrystalline silicon

Dylla

Finger

Schiff

2005

Applied Physics Letters

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We have measured transient photocurrents on several p-i-n solar cells based on microcrystalline silicon. For two of these samples, we were able to obtain conclusive hole drift-mobility measurements. Despite the predominant crystallinity of these samples, temperature-dependent measurements were consistent with an exponential-bandtail trapping model for transport, which is usually associated with noncrystalline materials. We estimated valence bandtail widths of about 31meV and hole band mobilities of 1–2cm2∕Vs. The measurements support mobility-edge transport for holes in these microcrystalline materials, and broaden the range of materials for which mobility-edge transport corresponds to an apparently universal band mobility of order 1cm2∕Vs.

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Section: Hole Drift-mobility Measurements In Microcrystalline Siliconmentioning

confidence: 99%

Hole drift-mobility measurements in microcrystalline silicon

Dylla

Finger

Schiff

2005

Applied Physics Letters

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“…However, the parameters were chosen so that the results can easily be adapted to hydrogenated amorphous silicon, for which DE V E48 me V [21,23]. The principal difficulty in applying the results from the last section is that the photogeneration in a solar cell is certainly not uniform, as was assumed; in this section we adapt the model to the case of solar illumination.…”

Section: Implications For Solar Conversion By Amorphous Siliconmentioning

confidence: 99%

“…These three parameters may be obtained from hole time-of-flight measurements such as the 1994 paper of Gu et al [23]. This paper proposed DE V =48 meV, m h 0 =0.27 cm 2 /V s, and an attempt-to-escape frequency n=7.7 Â 10 10 s; the product N V b T is equal to n. Unpublished work from Syracuse University [27] indicates that hole drift mobilities have increased in more modern samples, although no detailed description yet exists for how and why the three timeof-flight parameters vary in differing forms of a-Si:H. For simplicity, we use a valence band mobility m h 0 =1 cm 2 /V s and n=10 11 /s; the bandtail width is treated as a variable in the present work.…”

Section: Appendix D Solar Cell Modeling Parameters (With Valence Banmentioning

confidence: 99%

03/02418 Low-mobility solar cells: a device physics primer with application to amorphous silicon

2003

Fuel and Energy Abstracts

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The properties of pin solar cells based on photogeneration of charge carriers into lowmobility materials were calculated for two models. Ideal p-and n-type electrode layers were assumed in both cases. The first, elementary case involves only band mobilities and direct electron-hole recombination. An analytical approximation indicates that the power in thick cells rises as the 1 4 power of the lower band mobility, which reflects the buildup of space-charge under illumination. The approximation agrees well with computer simulation. The second model includes exponential bandtail trapping, which is commonly invoked to account for very low hole drift mobilities in amorphous silicon and other amorphous semiconductors. The two models have similar qualitative behavior. Predictions for the solar conversion efficiency of amorphous silicon-based cells that are limited by valence bandtail trapping are presented. The predictions account adequately for the efficiencies of present a-Si : H cells in their ''asprepared'' state (without light-soaking), and indicate the improvement that may be expected if hole drift mobilities (and valence bandtail widths) can be improved. r

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“…The empty dot is taken from Penchina (1965) in order to be consistent with the present data obtain by co-planar geometry. Please refer to Jiang, et al (1998) (Gu, et al, 1994) and for "triode" plasma deposited a Si:H from Electrotechnical Laboratory. The upper two regression lines represent the triodematerial; the open symbols represent prior measurements of Ganguly, et al (1996).____________________ 35 Fig.…”

Section: "High-field Electron-drift Measurements and The Mobilitymentioning

confidence: 99%

“…The hole mobilities are limited by trapping processes involving the valence bandtail. Remarkably, for the entire class of plasmadeposited amorphous silicon-germanium and amorphous silicon-carbon alloys deposited in "diode" reactors, representing many years of materials research, it has been found that the hole drift mobility remains nearly constant, with a best value of 2 × 10 -3 cm 2 /Vs under standard conditions (Gu, Wang, Schiff, Li, and Malone, 1994, and references therein).…”

Section: Introductionmentioning

confidence: 99%

Research on High-Bandgap Materials and Amorphous Silicon-Based Solar Cells, Final Technical Report, 15 May 1994-15 January 1998

Schiff¹,

Gu²,

Lin³

et al. 1998

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or DOE Information Bridge http://www.doe.gov/bridge/home.html Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste 1 Preface This research project had four broad objectives involving a variety of technical approaches:• We sought a deeper understanding of the open circuit voltage V OC in amorphous silicon based solar cells, and in particular for cells employing wide bandgap modification of amorphous silicon as their absorber layer. Our technical approach emphasized the development of electroabsorption measurements as a tool for probing the built-in potential of a-Si:H based solar cells.• We sought a better understanding of the optical properties of amorphous silicon and of microcrystalline silicon materials such as used in the p + layer of some advanced a-Si:H based solar cells. Electroabsorption spectroscopy appears to be useful for this purpose, and was a natural extension of the built-in potential research.• We sought to improve our understanding of the fundamental electron and hole photocarrier transport processes in the materials used for amorphous silicon based solar cells. Our technical approach was been to develop photocarrier time-of-flight measurements in solar cells.• We aimed to improve V OC in wide bandgap cells by searching for superior materials for the p-type "window layer" of the cell, and explored thin-film boron phosphide for this purpose.In addition to the authors of this report, we have reported work which includes the contributions of several collaborators, in particular Reinhard Schwarz, Stefan Grebner, and We have also benefitted from the cooperation and interest of several other scientists and organizations. In particular we thank Christopher Wronski at Pennsylvania State University, Steve Hegedus at the Institute of Energy Conversion, University of Delaware, and Murray Bennett at Solarex Corp. Thin Films Division. Summary• The built-in potential is a crucial device parameter for solar cells, and one which is only roughly known and understood for a-Si:H based cells. We have developed a technique based on electroabsorption measurements for obtaining quantitative estimates of the built-in potential in aSi:H based heterostructure solar cells incorporating microcrystalline or a-SiC:H p layers. This heterostructure problem has been a major limitation in application of the electroabsorption technique. The new technique only utilizes measurements from a particular solar cell, and is thus a significant improvement on earlier techniques requiring measurements on auxiliary films.• Using this new electroabsorption technique, we confirmed previous estimates of V bi ≈ 1.0 V in a-Si:H solar cells with "conventional" intrinsic layers and either microcrystalline or a-SiC:H p layers. Interestingly, our measurements on high V oc cells grown with "high hydrogen dilution" intrinsic layers yield a much larger value for V bi ≈ 1.3 V. We speculate that these results are evidence for a 2 significant interface dipole at the p/i heterostructure interface. Although we believe that i...

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Hole drift mobility measurements in amorphous silicon-carbon alloys

Cited by 48 publications

References 9 publications

Hole drift-mobility measurements in microcrystalline silicon

Hole drift-mobility measurements in microcrystalline silicon

03/02418 Low-mobility solar cells: a device physics primer with application to amorphous silicon

Research on High-Bandgap Materials and Amorphous Silicon-Based Solar Cells, Final Technical Report, 15 May 1994-15 January 1998

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