Non-Uniform Excitation PL-Imaging
Photoluminescence Imaging with Spatially Non-Uniform Excitation
Photoluminescence (PL) imaging is a fast and contactless technique that provides qualitative spatial non-uniformity of sample’s recombination properties. In standard PL imaging, a light source with spatially uniform intensity is used to excite the sample and the PL emitted from the sample is captured by an infra-red camera. In this project, we aim to further extend the capabilities of PL imaging by using spatially non-uniform light to excite the sample.
On the one hand, spatially non-uniform excitation can be used to intentionally induce lateral current into the sample in a contactless manner. This lateral current can then be used to extract information which cannot be obtained from conventional PL imaging, for example, the series resistance of solar cells. Previously, series resistance imaging is usually obtained by electroluminescence (EL) imaging or PL imaging with carrier extraction, both of which require electric contacts. However, by inducing lateral current via spatial non-uniform excitation, the series resistance imaging can now be obtained in a contactless way (See Fig. 1 for example). Other applications with this concept can be found in Ref. [1].
On the other hand, spatially non-uniform excitation can also be used to counterbalance the lateral carrier flow in the sample due to the spatially non-uniform recombination properties of the sample. In conventional PL imaging, since uniform excitation is used, there is lateral carrier flow from the high lifetime regions to low lifetime regions. This lateral carrier flow smears out the resulted images and also impedes the accurate PL imaging based quantitative analysis. In this project, we proposed an approach to adaptively adjust the spatial non-uniform excitation until a uniform PL image is achieved for a non-uniform sample [2]. The lateral carrier flow within the sample is then inherently removed and the non-uniformity information of the sample can be extracted from the applied non-uniform excitation image. Since lateral carrier flow is removed, the resulted image is much sharper than conventional PL image and more accurate for further quantitative analysis. This part of the project is also in collaboration with Fraunhofer ISE.
Related publications are:
- Yan Zhu, Mattias K. Juhl, Thorsten Trupke, Ziv Hameiri, Photoluminescence imaging of silicon wafers and solar cells with spatially inhomogeneous illumination, IEEE J. Photovoltaics 7, 1087 (2017).
- Friedemann D. Heinz, Yan Zhu, Ziv Hameiri, Mattias K. Juhl, Thorsten Trupke, Martin C. Schubert, The principle of adaptive excitation for photoluminescence imaging of silicon: theory, Phys. Status Solidi - Rapid Res. Lett. 1800137, 1800137 (2018).
Funding:
ARENA 2014/RND097
ARENA 2017/RND001
ARC DE150100268
CCPV by the German Federal Ministry of Research and Education
