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EBSDCharacterisation of all-oxide solar cells using AZtec® LayerProbe®

Application NoteEDSIntroduction

Composition and thickness measurements with AZtec LayerProbe

The layer structure of the all-oxide solar cell stack.

Photograph of the sample with the analysed area indicated by the rectangle.

AZtec LayerProbe measures layer thicknesses and compositions by fitting a user

defined model of the sample to an EDS spectrum obtained using the software.

As the thickness and composition is calculated from an EDS spectrum acquired

from the sample surface, LayerProbe is inherently non-destructive. This enables

subsequent testing and analysis of the sample, in this case, allowing the electrical

performance to be correlated with layer properties. LayerProbe’s high spatial

resolution permits analysis of features down to 200 nm wide with thicknesses

between 2 nm and 2000 nm. LayerProbe suggests the optimum SEM conditions for

a given analysis so that the highest quality results may be achieved.

Analysis of an All-Oxide Solar Cell Combinatorial Library

Photovoltaic (PV) cells are an attractive option for generating low carbon renewable energy but traditional

designs often include undesirable toxic compounds and must be manufactured under special conditions. The

all-oxide approach to photovoltaic cells is thus very attractive as it circumvents many of these issues and offers a

potential method of creating a lower cost, more widely used product. AZtec LayerProbe was used to characterise

a combinatorial library sample with varying layer thicknesses and compositions in order to determine which

combination is most effective [1].

The sample investigated here consisted of a glass substrate, a transparent

conductive oxide (TCO) layer (Fluorine doped SnO2), and as the active layers, a

TiO2 layer with a constant thickness gradient and a top layer with varying CuxNiyOz

composition and thickness. As such, the complete structure formed a combinatorial

library of PV devices each with a unique combination of active layer composition

and layer thickness.

In order to characterise layers in the sample, 208 EDS spectra were acquired from

the top of the sample over an area of 42 x 36 mm. LayerProbe was then used to

process the spectra. The starting model comprised of the layer sequence in the

sample and the composition of all layers bar the CuxNiyOz. The parameters which

were determined by LayerProbe were the thicknesses of the TCO and TiO2 layers,

and both the thickness and composition of the top CuxNiyOz layer.

The surface plots show the results of the LayerProbe measurements. The thickness

of the TCO layer was constant across the measured area, whereas that of the TiO2

layer varies linearly along the horizontal axis. The thickness of the CuxNiyOz layer has

a more complex profile which corresponds to the shading which can be seen in the

photograph of the sample (right).

EBSDApplication NoteEBSD

The materials presented here are summary in nature, subject to change, and intended for general information only. Performances are configuration dependent. Additional details are available. Oxford Instruments NanoAnalysis Quality Management System is certified to meet ISO 9001: 2008. INCA is a Registered Trademark of Oxford Instruments plc , all other trademarks acknowledged.© Oxford Instruments plc, 2013. All rights reserved. Document reference: OINA/PV/0912

EDSAsbestos analysis in the TEM

www.oxford-instruments.com/layerprobe

Conclusion

The use of LayerProbe here has allowed the rapid and cost effective quantification of layer thickness and composition at 208

points in a non-destructive manner. As the combination of thickness and composition is different at each of these points, a

large library of combinations has been analysed in a single sample. This data, combined with electro-optical characterisation

of individual solar cell devices enables the rapid testing and development of new combinations of materials thereby bringing

forward the release of increasingly economically viable devices.

References:[1] S Rühle et al, J. Phys. Chem. Lett. 3 (2012) p. 3755.

This work was carried out in collaboration with S. Rühle, A. Y. Anderson and A. Zaban from the All-Oxide Photovoltaics Project, Bar Ilan Center for Nanotechnology and Advanced Materials, Bar Ilan University, Ramat Gan 52900, Israel.

Surface plots show the layer thickness obtained using LayerProbe of the TCO layer, the TiO2 layer and the CuxNiyOz layer respectively. The Cu/Ni ratio is that in the CuxNiyOz layer.