Depth dependent optoelectronic properties of Cu(In,Ga)Se2 with lateral resolution in the micron/submicron scale from luminescence studies

Bauer, G.H.; Heise, Stephan J.; Knabe, Sebastian; Neumann, O.; Brüggemann, R.; Hariskos, Dimitrios; Witte, Wolfram

doi:10.1016/j.egypro.2011.10.179

Cited by 8 publications

(7 citation statements)

References 3 publications

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“…If we compare the full‐width‐half‐maximum (fwhm) of our QFL‐splitting with the results in Refs. (sample A) and (sample B), obtained on similar samples, we find that our evaluation shows a 50% smaller fwhm in both cases. This indicates that the authors used different calibration functions

C false(ℏ ω false)

and thus a

η \neq 1

during the evaluation procedure.…”

Section: Resultssupporting

confidence: 55%

See 1 more Smart Citation

Avoiding arbitrarily wrong microluminescence statistics due to a non-quantitatively calibrated setup

Sträter

Nilius

Brüggemann

2017

Phys. Status Solidi B

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Photoluminescence (PL) measurements on the normalμm scale are a powerful tool to examine thin film semiconductors with respect to lateral inhomogeneities of their opto‐electronic properties. For practical reasons, the determination of the standard deviation of the laterally resolved splitting of quasi‐Fermi levels (QFL) is often performed with an experimental setup that only has been calibrated spectrally but not with respect to the quantitatively emitted photon flux. We show that the omission of the absolute PL photon flux can lead to arbitrarily wrong distributions of the QFL‐splitting and correlations between the QFL‐splitting and other opto‐electronic properties. For a better understanding, we present a algebraical formalism of the dependence on the absolute calibration and demonstrate the effect of a wrong calibration using two different thin film absorbers. Finally, a method to estimate the true statistics with sufficient accuracy is presented.

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C false(ℏ ω false)

and thus a

η \neq 1

during the evaluation procedure.…”

Section: Resultssupporting

confidence: 55%

“…Nevertheless, for comparison of the lateral inhomogeneities of several samples or different positions on one sample, as shown in Refs. , an estimation of the quantitative calibration has to be taken into account. Despite wrong absolute numbers, even general trends can be flipped for totally wrong values of

η

.…”

Section: Mathematical Frameworkmentioning

confidence: 99%

Avoiding arbitrarily wrong microluminescence statistics due to a non-quantitatively calibrated setup

Sträter

Nilius

Brüggemann

2017

Phys. Status Solidi B

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“…The resulting PL spectra revealed no energy shift of the peak, underlining our findings that the luminescence originates from the band gap notch inside the absorber film. Furthermore, Bauer et al conducted etching and subsequent PL experiments on absorbers, whose band gap showed a minimum inside the bulk but no surface band gap minimum and came to a similar conclusion [23]. To summarize, the exfoliation experiments have shown that the PL is originating from the band gap minimum inside the bulk of the CIGS absorbers.…”

Section: Origin Of Photoluminescencementioning

confidence: 87%

Influence of Sodium and Rubidium Postdeposition Treatment on the Quasi-Fermi Level Splitting of Cu(In,Ga)Se₂Thin Films

Wolter

Bissig

Avancini

et al. 2018

IEEE J. Photovoltaics

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The influence of sodium and rubidium postdeposition treatment on the quality of Cu(In,Ga)Se 2 thin-film absorbers is investigated. The quasi-Fermi level splitting (QFLS), measured via photoluminescence (PL), is used as the metric of quality of the absorber. To evaluate the QFLS values in the graded absorber of state-of-the-art devices, it is necessary to know at which location the luminescence is generated. Here we show, by measuring the PL in different geometries, that the photons originate from the global band gap minimum inside the bulk. We use this knowledge to compare the QFLS in different absorbers, where our results show that the QFLS is higher in absorbers that were treated with NaF + RbF than in absorbers that were only treated with NaF or not treated at all. We attribute this increase to a reduced nonradiative recombination, even before cadmium sulfide deposition. A decreased difference between QFLS and open-circuit voltage in the corresponding finished solar cells also reveals an improved CdS/CIGS interface. Both effects ultimately lead to a higher efficiency. I. INTRODUCTION T HE beneficial effects of alkali elements, especially sodium, on the performance of chalcopyrite solar cells based on Cu(In,Ga)Se 2 (CIGS) absorbers were discovered more than 20 years ago [1]. It was found that Na naturally diffuses from the alkali containing soda lime glass (SLG) substrate into the absorber during the high-temperature growth process. In solar cells grown on alkali-free substrates, such as the flexible polyimide films, the alkali elements would need to be added extrinsically in order

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“…Photoluminescence measurements in a confocal arrangement or with a scanning near‐field optical microscope allow to record lateral fluctuations in the micron and submicron range . From such PL studies, local spectral absorption/absorption coefficients and the local splitting of the quasi‐Fermi levels of electrons and holes, E Fn − E Fp , can be extracted according to Planck's generalized law , where E Fn − E Fp = k B T ln( np / n i 2 ) with Boltzmann constant k B , temperature T , electron concentration n , hole concentration p and intrinsic carrier concentration n i 2 = N C N V exp(− E g / k B T ) including the effective densities of states N C and N V .…”

Section: Depth‐dependent Characterization Of Lateral Inhomogeneities mentioning

confidence: 99%

“…Figure depicts the distributions of E Fn − E Fp (a) and ε g (b) of the glass/CIGS/CdS samples from the etch series with a Ga gradient of the as‐grown sample on glass (not shown here) very similar to the gradient depicted in Figure (c) on glass/Mo. These etched samples are expected to exhibit different CIGS/CdS interfaces compared to the as‐grown absorber ( d = 2.2 µm) and consequently different quasi‐Fermi level splitting . The distributions shift energetically with decreasing thicknesses of the absorber layer (black arrows).…”

Section: Depth‐dependent Characterization Of Lateral Inhomogeneities mentioning

confidence: 99%

Gallium gradients in Cu(In,Ga)Se₂thin-film solar cells

Witte

Abou‐Ras

Albe

et al. 2014

Prog. Photovolt: Res. Appl.

133

100

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The gallium gradient in Cu(In,Ga)Se2 (CIGS) layers, which forms during the two industrially relevant deposition routes, the sequential and co‐evaporation processes, plays a key role in the device performance of CIGS thin‐film modules. In this contribution, we present a comprehensive study on the formation, nature, and consequences of gallium gradients in CIGS solar cells. The formation of gallium gradients is analyzed in real time during a rapid selenization process by in situ X‐ray measurements. In addition, the gallium grading of a CIGS layer grown with an in‐line co‐evaporation process is analyzed by means of depth profiling with mass spectrometry. This gallium gradient of a real solar cell served as input data for device simulations. Depth‐dependent occurrence of lateral inhomogeneities on the µm scale in CIGS deposited by the co‐evaporation process was investigated by highly spatially resolved luminescence measurements on etched CIGS samples, which revealed a dependence of the optical bandgap, the quasi‐Fermi level splitting, transition levels, and the vertical gallium gradient. Transmission electron microscopy analyses of CIGS cross‐sections point to a difference in gallium content in the near surface region of neighboring grains. Migration barriers for a copper‐vacancy‐mediated indium and gallium diffusion in CuInSe2 and CuGaSe2 were calculated using density functional theory. The migration barrier for the InCu antisite in CuGaSe2 is significantly lower compared with the GaCu antisite in CuInSe2, which is in accordance with the experimentally observed Ga gradients in CIGS layers grown by co‐evaporation and selenization processes. Copyright © 2014 John Wiley & Sons, Ltd.

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Depth dependent optoelectronic properties of Cu(In,Ga)Se2 with lateral resolution in the micron/submicron scale from luminescence studies

Cited by 8 publications

References 3 publications

Avoiding arbitrarily wrong microluminescence statistics due to a non-quantitatively calibrated setup

Avoiding arbitrarily wrong microluminescence statistics due to a non-quantitatively calibrated setup

Influence of Sodium and Rubidium Postdeposition Treatment on the Quasi-Fermi Level Splitting of Cu(In,Ga)Se₂Thin Films

Gallium gradients in Cu(In,Ga)Se₂thin-film solar cells

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Depth dependent optoelectronic properties of Cu(In,Ga)Se2 with lateral resolution in the micron/submicron scale from luminescence studies

Cited by 8 publications

References 3 publications

Avoiding arbitrarily wrong microluminescence statistics due to a non-quantitatively calibrated setup

Avoiding arbitrarily wrong microluminescence statistics due to a non-quantitatively calibrated setup

Influence of Sodium and Rubidium Postdeposition Treatment on the Quasi-Fermi Level Splitting of Cu(In,Ga)Se2Thin Films

Gallium gradients in Cu(In,Ga)Se2thin-film solar cells

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Product

Resources

About

Influence of Sodium and Rubidium Postdeposition Treatment on the Quasi-Fermi Level Splitting of Cu(In,Ga)Se₂Thin Films

Gallium gradients in Cu(In,Ga)Se₂thin-film solar cells