The efficiency result represents one of the best performances achieved to date for this type of thin-film solar cells. The device is manufactured with a contact interface on the back that reportedly improves charge transport.
Researchers from Chonnam National University in South Korea have used vapor processing to deposit a germanium oxide layer on the back contact surface of thin-film tin mon sulfide (SnS) solar cells to improve the energy conversion efficiency of solar cells to 4.81%, up from 3.7% for the standard cell.
Although known as a cheap, plentiful material with promising properties for use in solar cells, tin monosulfide (SnS) has proven to be a challenging material to work with, and researchers have thus far struggled to achieve conversion efficiencies above 5% with this material, and interest from the research community has lagged behind that of kesterite, or copper-zinc-tin, solar cells.
The team fabricated the cell by depositing a 7-nanometer layer of germanium oxide (GeOx) between the molybdenum back contact and the SnS absorber layer in a process that involved interface engineering, defect passivation and contact optimization “to translate material advances into stable, high-performance devices suitable for scalable photovoltaic applications,” according to the study’s corresponding author Jaeyeong Heo.
“Our team in South Korea has been actively working on thin-film solar cells for many years, with a strong focus on earth-rich and environmentally friendly absorbers such as kesterite, SnS and related chalcogenides,” Heo said. pv magazine.
The group selected SnS not only for its abundant, non-toxic characteristics, but also because it has a “near-ideal bandgap” of ~1.3 eV and a “strong optical absorption” of ~104 cm-1, according to Heo, who also highlighted that SnS thin-film devices “have historically underperformed due to interface losses and defect-related recombination rather than intrinsic material limitations.”
The experimental device stack was as follows: soda lime glass, molybdenum contact layer, GeOx, SnS absorber, cadmium sulfide (CdS) buffer layer, intrinsic zinc oxide (i-ZnO), aluminum doped zinc oxide (AZO) window layer, aluminum metal contact.
During testing, the researchers noted that the vapor transport deposition process provided a way to passivate deep defects and suppress sodium diffusion on the substrate, enabling “larger, more uniform grains,” improved charge transport and a reduction in electrical losses to achieve the “substantial” increase in energy conversion efficiency,” yielding a PCE of 4.81%, one of the highest values reported for SnS-based “thin-film” solar cells, the researchers noted on.
As described in the study: “Backside passivation using a controlled germanium oxide (GeOₓ) interlayer”, published in Smallsubsequent stability testing of the device was performed three months after manufacture. A device without encapsulation retained more than 96% of its original efficiency, demonstrating “excellent long-term stability.”
Previous research addressed other performance bottlenecks through targeted interface and surface engineering. Last year, for example, the group reported Journal of Materials Chemistry A a sulfur prebaking approach, which clarified the “critical role of sulfur stoichiometry control” in improving film quality and photovoltaic performance.
“Looking ahead, our team plans to integrate these individual developments into unified device architectures by combining optimized source engineering, surface treatments and contact passivation into a single platform,” said Heo. Research topics include developing physics-based models, deposition technology and exploring SnS-based tandem, quantum dots-based or hybrid device concepts.
“Ultimately, our goal is to establish SnS as a competitive, earth-abundant thin-film technology that offers both high efficiency and long-term stability, making it suitable for real-world deployment,” Heo said.
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