Carrier-Resolved Photo-Hall Analysis of Selenium Thin Films and Solar Cells

Selenium has reemerged as a promising absorber material for a range of applications due to its elemental simplicity, unique structural features, and exceptional optoelectronic properties. With a wide direct bandgap of 1.8-2.0 eV, selenium is an ideal candidate for indoor solar cells and as the top cell in tandem photovoltaic devices^[1]. Furthermore, research activity on selenium is accelerating, as evidenced by the rapidly increasing device efficiencies being reported^[2]. However, despite this renewed focus, the carrier properties of selenium remain poorly understood, limiting the realization of its full potential as a high-efficiency photovoltaic material.
Here, we build on our fundamental understanding of both the majority and minority carriers by simultaneously mapping their properties using a high-sensitivity, variable-temperature photo-Hall system^[3]. The results are compared and integrated with those from other advanced characterization tools, including transient THz spectroscopy, capacitance-based techniques, and voltage-dependent quantum efficiency measurements. To systematically resolve the identified discrepancies, we construct semiconductor physics models that account for non-idealities at interfaces and surfaces, perform device simulations, and accurately reproduce experimental JV-curves and EQE-spectra. By providing a holistic view of carrier dynamics and non-idealities in state-of-the-art selenium thin films, we reveal the current performance limitations and delineate pathways to significantly enhance the efficiency of selenium solar cells.

[1] R. Nielsen, A. Crovetto, A. Assar, O. Hansen, I. Chorkendorff, P. C. K. Vesborg, Monolithic Selenium/Silicon Tandem Solar Cells, PRX Energy 3 (1), 013013 (2024)
[2] W. Lu, M. Feng, Z. Li, B. Yan, S. Wang, X. Wen, Z. An, S. Liu, J. Hu, D. Xue, Ordering one-dimensional chains enables efficient selenium photovoltaics, Joule 8 (5), 1430-1442 (2024)
[3] R. S. Nielsen, O. Gunawan, T. Todorov, C. B. Møller, O. Hansen, P. C. K. Vesborg, Variable Temperature and Carrier-Resolved Photo-Hall Measurements of High-Performance Selenium Thin-Film Solar Cells, arXiv:2409.12804 (2024)