Monolithic Selenium/Silicon Tandem Solar Cells

Abstract

Selenium is experiencing renewed interest as a promising candidate for the wide bandgap photoabsorber in tandem solar cells. However, despite the potential of selenium-based tandems to surpass the theoretical efficiency limit of single-junction devices, such a device has never been demonstrated. In this study, we present the first monolithically integrated selenium/silicon tandem solar cell. Guided by device simulations, we investigate various carrier-selective contact materials and achieve encouraging results, including an open-circuit voltage of Voc=1.68V from suns-Voc measurements. The high open-circuit voltage positions selenium/silicon tandem solar cells as serious contenders to the industrially dominant single-junction technologies. Furthermore, we quantify a pseudo fill factor of more than 80% using injection-level-dependent open-circuit voltage measurements, indicating that a significant fraction of the photovoltaic losses can be attributed to parasitic series resistance. This work provides valuable insights into the key challenges that need to be addressed for realizing higher efficiency selenium/silicon tandem solar cells. Published by the American Physical Society 2024

Increasing the Collection Efficiency in Selenium Thin-Film Solar Cells Using a Closed-Space Annealing Strategy

“…Our previous work highlighted the necessity of crystallizing the as-deposited selenium thin film prior to the deposition of MoO x to avoid the formation of cracks in the absorber. 8 Therefore, we annealed the SLG/FTO/ ZnMgO/a-Se structure for 4 min at 190 °C to transform the amorphous selenium (a-Se) into a polycrystalline selenium (poly-Se) thin film of the desired trigonal phase, followed by the deposition of MoO x and the gold electrode. Given that the MoO x thin film only partially covers the poly-Se thin film, we expect the unprotected edges of the absorber to sublimate during higher-temperature annealing processes.…”

“…To assess the effectiveness of MoO x as an encapsulating material, we deposited each thin film in our devices with successively smaller aperture areas, as illustrated in Figure B. Our previous work highlighted the necessity of crystallizing the as-deposited selenium thin film prior to the deposition of MoO x to avoid the formation of cracks in the absorber . Therefore, we annealed the SLG/FTO/ZnMgO/a-Se structure for 4 min at 190 °C to transform the amorphous selenium (a-Se) into a polycrystalline selenium (poly-Se) thin film of the desired trigonal phase, followed by the deposition of MoO x and the gold electrode.…”

“…Selenium is experiencing renewed interest as an inorganic photovoltaic material for the next generation of thin-film solar cells. , With a direct bandgap of 1.95 eV and high absorption coefficient in its trigonal phase, selenium is potentially an ideal candidate for the photoabsorbing layer in indoor solar cells, − as well as the top cell in tandem devices. , Furthermore, as selenium crystallizes at approximately 120 °C and melts at 220 °C, the temperatures needed for processing are relatively low in comparison with other chalcogenide-based absorber materials . This makes selenium compatible with most substrates and bottom cell candidates and facilitates the production of low-cost solar cells.…”

Testing a New Solar Sandwich

“…One challenging but promising way to increase this efficiency is to make solar cells from multiple materials with different photon-absorption properties, which would allow them to absorb more sunlight. Rasmus Nielsen of the Technical University of Denmark and his colleagues have done just that, demonstrating a solar cell that combines silicon with selenium, the first photovoltaic material to be discovered [1]. The researchers say that with updates, the performance of their selenium/silicon device could soon rival today's best silicon cells.…”