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Impact of the Annealing Temperature on the Local Se Distribution and Optical Properties in CdSexTe1−x Solar Cells by Multimodal X-ray Microscopy

Jackson L. Barp, Jr.1,2, Gero Falkenberg1,2, Giovanni Fevola1, Svenja Patjens1, Niklas Pyrlik1,2, Sven Hampel1, Eric Colegrove3, Andrea Mathew3,4, Jan Garrevoet5 et al.

Gerald Falkenberg5, Christian Strelow6, Tobias Kipp6, Christian G. Schroer1,2,7, and Michael E. Stuckelberger1,*

  • *Contact author: michael.stuckelberger@desy.de
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PRX Energy 5, 033011 – Published 13 August, 2026

DOI: https://doi.org/10.1103/56gn-4mgn

Abstract

The introduction of Se in CdTe solar-cell absorbers has led to multiple beneficial effects in the devices, including an increased short-circuit current and an extended charge-carrier lifetime. A critical manufacturing step of CdSexTe1−x solar cells is CdCl2 annealing at high temperatures, during which Se diffuses through the absorber layer. Understanding the local Se distribution in the absorber and its impact on optical properties of the material is key for the further development of this thin-film solar cell technology. In a multimodal x-ray scanning microscopy approach, we investigated the impact of the annealing temperature of CdSexTe1−x solar cells on the Se distribution and on optical characteristics of the material. For this purpose, we exploited an upgraded x-ray excited optical luminescence (XEOL) detection unit that enables simultaneous spectrally and temporally resolved XEOL mapping at synchrotron facilities that are ideal for studying thin-film solar-cell materials with hard x-rays featuring high penetration depth and lateral resolution.

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Modern thin-film solar cells based on cadmium telluride (CdTe) can be made more efficient by adding small amounts of selenium. This improves the efficiency of the cells and enhances the charge-carrier lifetime. A key step in manufacturing these solar cells involves heating them to high temperatures under a CdCl2 environment, which causes selenium to spread through the active layer of the device. However, until now, it has been difficult to directly observe how this selenium distribution varies across the solar cell and how it affects the device performance. In this study, the authors use advanced X-ray microscopy to visualize how selenium is distributed inside CdSeTe solar cells and how this distribution changes with the processing temperature. They reveal how local variations in selenium influence important material properties, such as band-gap energy and charge-carrier lifetime. These results provide new insight into how processing conditions shape the internal composition and performance of thin-film solar cells, helping guide the development of more efficient and reliable solar energy technologies.

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PRX Energy 5, 033011– Published 13 August, 2026
  • Received 30 December 2025
  • Revised 24 April 2026
  • Accepted 1 July 2026
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