In-situ Raman spectroscopy used to study and control the initial growth phase of microcrystalline absorber layers for thin-film silicon solar cells

Muthmann, Stefan; Köhler, Florian; Meier, Matthias; Hülsbeck, Markus; Carius, R.; Gordijn, A.

doi:10.1016/j.jnoncrysol.2011.12.061

Cited by 4 publications

(4 citation statements)

References 23 publications

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“…This property is indeed an advantage over PL and facilitates the estimation of the volume fraction between small and large Si-NCs. 16,19 In the literature, a number of models are developed to describe influence of nanocrystal size on the broadening and shift of the phonon peak. 12,20,21 Two models to describe the nanocrystal size according to the shift of the phonon peak are the bond polarizability model (BPM), 21 and the modified one-phonon confinement model (PCM).…”

Section: Introductionmentioning

confidence: 99%

Direct characterization of nanocrystal size distribution using Raman spectroscopy

Doğan

Sanden

2013

Journal of Applied Physics

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We report a rigorous analytical approach based on one-particle phonon confinement model to realize direct detection of nanocrystal size distribution and volume fraction by using Raman spectroscopy. For the analysis, we first project the analytical confinement model onto a generic distribution function, and then use this as a fitting function to extract the required parameters from the Raman spectra, i.e., mean size and skewness, to plot the nanocrystal size distribution. Size distributions for silicon nanocrystals are determined by using the analytical confinement model agree well with the one-particle phonon confinement model, and with the results obtained from electron microscopy and photoluminescence spectroscopy. The approach we propose is generally applicable to all nanocrystal systems, which exhibit size-dependent shifts in the Raman spectrum as a result of phonon confinement.

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Section: Introductionmentioning

confidence: 99%

Direct characterization of nanocrystal size distribution using Raman spectroscopy

Doğan

Sanden

2013

Journal of Applied Physics

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“…In association with the substrate nature, the nucleation of μc-Si:H as well as the initial growth of a-Si:H thin-films has been mainly attributed to the substrate chemistry, thereby considering e.g. crystallinity, conductivity, surface free energy [9][10][11][12][13][14][15][16][17][18][19], and the impact of plasma-surface interactions [12,20]. On the other hand, optimized light trapping schemes result in enhanced light absorption by manipulating the optical path length of the incoming light [21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Nucleation of microcrystalline silicon: on the effect of the substrate surface nature and nano-imprint topography

Palmans

Faraz

Verheijen

et al. 2016

J. Phys. D: Appl. Phys.

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The nucleation of microcrystalline silicon thin-films has been investigated for various substrate natures and topographies. An earlier nucleation onset on aluminium-doped zinc oxide compared to glass substrates has been revealed, associated with a microstructure enhancement and reduced surface energy. Both aspects resulted in a larger crystallite density, following classical nucleation theory. Additionally, the nucleation onset was (plasma deposition) condition-dependent. Therefore, surface chemistry and its interplay with the plasma have been proposed as key factors affecting nucleation and growth. As such, preliminary proof of the substrate nature's role in microcrystalline silicon growth has been provided. Subsequently, the impact of nano-imprint lithography prepared surfaces on the initial microcrystalline silicon growth has been explored. Strong topographies, with a 5-fold surface area enhancement, led to a reduction in crystalline volume fraction of ~20%. However, no correlation between topography and microstructure has been found. Instead, the suppressed crystallization has been partially ascribed to a reduced growth flux, limited surface diffusion and increased incubation layer thickness, originating from the surface area enhancement when transiting from flat to nanostructured surfaces. Furthermore, fundamental plasma parameters have been reviewed in relation with surface topography. Strong topographies are not expected to affect the ion-to-growth flux ratio. However, the reduced ion flux (due to increasing surface area) further limited the already weak ion energy transfer to surface processes. Additionally, the atomic hydrogen flux, i.e. the driving force for microcrystalline growth, has been found to decrease by a factor of 10 when transiting from flat to nanostructured topography. This resulted in an almost 6-fold reduction of the hydrogen-to-growth flux ratio, a much stronger effect than the ion-to-growth flux ratio. Since previous studies regarding crystalline growth stated the necessity for enhanced ion-and atomic hydrogen-to-growth flux ratios, reduction of the latter is suggested to be the main cause of suppressed crystallization kinetics.

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“…Muthmann et al reported on the capabilities of that technique to study the Raman crystallinity during the initial growth phase and to observe the effect of an adjusted silane to hydrogen ratio. 32 Here, we monitor the evolution of the Raman crystallinity throughout the entire intrinsic layer. The inhomogeneous absorber layer growth is successively compensated by an iterative readjustment of the process settings and the impact on the solar cell parameters is discussed.…”

Section: Introductionmentioning

confidence: 99%

Interplay between crystallinity profiles and the performance of microcrystalline thin-film silicon solar cells studied by in-situ Raman spectroscopy

Fink

Muthmann

Mück

et al. 2015

Journal of Applied Physics

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The intrinsic microcrystalline absorber layer growth in thin-film silicon solar-cells is investigated by in-situ Raman spectroscopy during plasma enhanced chemical vapor deposition. In-situ Raman spectroscopy enables a detailed study of the correlation between the process settings, the evolution of the Raman crystallinity in growth direction, and the photovoltaic parameters η (solar cell conversion efficiency), JSC (short circuit current density), FF (fill factor), and VOC (open circuit voltage). Raman spectra were taken every 7 nm of the absorber layer growth depending on the process settings. The Raman crystallinity of growing microcrystalline silicon was determined with an absolute error of approximately ±5% for total absorber layer thicknesses >50 nm. Due to this high accuracy, inherent drifts of the Raman crystallinity profiles are resolvable for almost the entire absorber layer deposition. For constant process settings and optimized solar cell device efficiency Raman crystallinity increases during the absorber layer growth. To compensate the inhomogeneous absorber layer growth process settings were adjusted. As a result, absorber layers with a constant Raman crystallinity profile — as observed in-situ — were deposited. Solar cells with those absorber layers show a strongly enhanced conversion efficiency by ∼0.5% absolute. However, the highest FF, VOC, and JSC were detected for solar cells with different Raman crystallinity profiles. In particular, fill factors of 74.5% were observed for solar cells with decreasing Raman crystallinity during the later absorber layer growth. In contrast, intrinsic layers with favorable JSC are obtained for constant and increasing Raman crystallinity profiles. Therefore, monitoring the evolution of the Raman crystallinity in-situ provides sufficient information for an optimization of the photovoltaic parameters with surpassing depth resolution.

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In-situ Raman spectroscopy used to study and control the initial growth phase of microcrystalline absorber layers for thin-film silicon solar cells

Cited by 4 publications

References 23 publications

Direct characterization of nanocrystal size distribution using Raman spectroscopy

Direct characterization of nanocrystal size distribution using Raman spectroscopy

Nucleation of microcrystalline silicon: on the effect of the substrate surface nature and nano-imprint topography

Interplay between crystallinity profiles and the performance of microcrystalline thin-film silicon solar cells studied by in-situ Raman spectroscopy

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