Relationship between carrier diffusion lengths and defect density in hydrogenated amorphous silicon

Sakata, Isao; Yamanaka, Mitsuyuki; Sekigawa, Toshihiro

doi:10.1063/1.363888

Cited by 18 publications

(6 citation statements)

References 16 publications

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“…Typically, (mt) maj increases with decreasing E c À E f [39] accompanied by a decrease in (mt) min . This anticorrelated behavior is also seen when the electrons are the minority carriers in p-type a-Si:H, where (mt) min decreases with increasing E c À E f > 0.8 eV [36,40,41,46].…”

Section: Fermi-level Positionmentioning

confidence: 71%

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Steady‐State Photocarrier Grating Method

Brüggemann

2011

Advanced Characterization Techniques for Thin Film Solar Cells

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The excess-carrier properties of a photoexcited semiconductor are important indicators of its quality with respect to applications in optoelectronic devices or for studying the recombination physics. In contrast to the majority-carrier properties, which can be determined rather straightforwardly by stationary photocurrent measurements, the minority-carrier properties can only be revealed by more sophisticated methods. In this respect the steady-state photocarrier grating (SSPG) method has had an enormous impact since it was suggested by Ritter, Zeldov, and Weiser, named RZW hereafter, in 1986 [1].The SSPG method is based on the carrier diffusion under the presence of a spatial sinusoidal modulation in the photogeneration rate G, which induces a so-called photocarrier grating. From photocurrent measurements at different grating periods L, the ambipolar diffusion lengthL can be determined by an analysis that assumes ambipolar transport and charge neutrality.The proposal by RZW, following papers on the analysis [2, 3] and the simple setup triggered a rapid widespread application [4][5][6][7][8]. In parallel, critical and more in-depth accounts on the underlying theory were given to put the technique on a firm ground or to describe its limits when applied to semiconductors with traps. Ritter et al. [9], Balberg et al. [10, 11], Li [12], and Shah et al. [13] analyzed the transport equations, also with respect to the lifetime or relaxation time regimes. In the lifetime regime, the carrier lifetimes are longer than the dielectric relaxation time. The previous publications were later criticized by Hattori et al. [14] who performed a second-order perturbation approach and pointed out deficiencies of other earlier analyses. Nevertheless, Hattori et al. showed that under the conditions in the lifetime regime the analysis and evaluation of the SSPG method are correct. These authors also suggested a correction method to avoid incorrect values of L.A novel aspect was introduced by Abel and Bauer [15] who numerically solved the transport and Poisson equations and compared the solutions with a generalized theory which enables to study the SSPG results by the variation of L and/or electric j177 field E. These authors derive their expressions in terms of the mobility-lifetime product ðmtÞ min of the minority carriers, which can be determined from the SSPG method and related to L.More recently, Schmidt and Longeaud [16] developed a generalized derivation of the solution of the SSPG equations at low E. They identified the shortcomings in the previous derivations which differ from the numerical solution. Their approach also allows the SSPG experiment to be used for the density-of-states (DOS) determination.An important aspect is the above-mentioned association of L with the ðmtÞ min product of the minority carriers. Together with the majority-carrier mobility-lifetime product ðmtÞ maj at the same G from the photoconductivity s ph via s ph ¼ eGðmtÞ maj , where e equals 1.6 Â 10 À19 C, the excess-carrier properties can be related to e...

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Section: Fermi-level Positionmentioning

confidence: 71%

“…Sakata et al [46] argued that errors have been made in the determination of L by Wang and Schwarz [45] because the measured L by SSPG should be corrected. They maintain that there is a drop in the true diffusion length also in the initial stages of degradation.…”

Section: Defects and Light-induced Degradationmentioning

confidence: 99%

Steady‐State Photocarrier Grating Method

Brüggemann

2011

Advanced Characterization Techniques for Thin Film Solar Cells

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“…Here, we scanned the monitor height with its width unchanged (i.e., P = 380 nm) in the single‐pass case and obtained L abs = 261.5 and 90.6 nm in our solar cell [Figure (a)] and in the conventional planar one [Figure (b)]. As mentioned before, the hole diffusion length is only 50 nm after light soaking , which throughout the paper is set to the a‐Si:H layer thickness to avoid significant Staebler–Wronski effect . It is clearly seen that L abs is about 4.23 times (only about 0.81 times) larger than the hole diffusion length in our solar cell design (in the conventional planar design).…”

Section: Simulation Results and Discussionmentioning

confidence: 87%

“…The p‐i‐n a‐Si:H layers are deposited in sequence on the TCO electrode, whose nanopattern is assumed to be uniformly transformed into the a‐Si:H layers. In this paper, the a‐Si:H layer thickness, h Si , is set to 50 nm, i.e., h Si = 50 nm, which is equal to the hole diffusion length after light soaking with assumption of an average defect density of about 1 × 10 16 cm ‐3 due to the dangling bonds in the a‐Si:H layers . In this case, the photocarriers generated in the i‐type region can completely transport to the n‐type and p‐type regions of the a‐Si:H layers, and thus the light‐induced Staebler–Wronski effect can be reduced efficiently.…”

Section: Structure and Numerical Simulation Methodsmentioning

confidence: 99%

Optimal design of ultra‐broadband, omnidirectional, and polarization‐insensitive amorphous silicon solar cells with a core‐shell nanograting structure

Yang

Okuno

et al. 2012

Progress in Photovoltaics

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We systematically investigated the optical behaviors of an amorphous silicon solar cell with a core‐shell nanograting structure. The horizontally propagating Bloch waves and Surface Plasmon Polariton waves lead to significant absorption enhancements and consequently short‐circuit current enhancements of this structure, compared with the conventional planar one. The perpendicular carrier collection makes this structure optically thick and electronically thin. An optimal design is achieved through full‐field numerical simulation, and a physical explanation is given. Our numerical results show that this configuration has ultra‐broadband, omnidirectional, and polarization‐insensitive responses and has a great potential in photovoltaics. Copyright © 2012 John Wiley & Sons, Ltd.

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“…For good collection, thickness of device should be lesser than drift length ( ). For example, amorphous silicon has very low diffusion length [126][127][128], hence it's not possible to have 100 micrometer thick films. Nevertheless amorphous silicon has high absorption coefficient and thin film solar cells with thickness ~ 1um can be made using PIN structures.…”

Section: Field Based Collectionmentioning

confidence: 99%

Vapor grown Perovskite solar cells

Abbas¹

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Relationship between carrier diffusion lengths and defect density in hydrogenated amorphous silicon

Abstract: Defect density and atomic bond structure of tetrahedral amorphous carbon (ta-C) films prepared by filtered vacuum arc process

Cited by 18 publications

References 16 publications

Steady‐State Photocarrier Grating Method

Steady‐State Photocarrier Grating Method

Optimal design of ultra‐broadband, omnidirectional, and polarization‐insensitive amorphous silicon solar cells with a core‐shell nanograting structure

Vapor grown Perovskite solar cells

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