Developed by an international research team, the cell features a cadmium sulfide electron transport layer produced using a novel ozone doping strategy. This treatment improves the purity and stability of the material while increasing the energy band gap of cadmium sulfide.
A group of researchers from China’s Fujian Normal University and the University of Surrey in the United Kingdom have developed a carbon-based antimony trisulfide (Sb2S3) solar cell that achieved a record-breaking energy conversion efficiency of 9.0%.
“We set a new benchmark for this cheap and stable device architecture,” said the study’s lead author, Guilin Chen pv magazinenoting that the result represents a world record for this cell type.
Although Sb2S3 devices have a theoretical efficiency limit of 26% under radiation conditions, defects in the absorber material typically limit their performance to approximately 8%. “Our work provides a facile, scalable, and multifunctional engineering strategy for the electron transport layer (ETL) that not only breaks a performance bottleneck but also significantly improves device stability, representing an important step toward commercially viable, low-cost Sb2S3 solar photovoltaics,” Chen explained.
Sb₂S₃ cells are typically constructed with a cadmium sulfide (CdS) ETL, but the doping and layer thickness often affect both open-circuit voltage and short-circuit current.
“Through Situ Ozone Treatment (IOT), we have developed a one-step method for oxygen doping of the CdS electron transport layer (ETL) during the standard chemical bath deposition (CBD) process, eliminating the need for complex, high temperature or post-deposition treatments.,” Chen explained.
The proposed approach is said to suppress the typical Sb2O3 impurities, because it induces a hexagonal to cubic phase transition in CdS, which thermodynamically adversely affects the epitaxial growth of the harmful Sb2O3 impurity phase during absorber deposition, leading to a purer, higher quality absorber.
Furthermore, it reportedly creates an oxygen-rich, graded Cd layer at the buried interface between the CdS layer itself and the substrate made of glass coated with fluorine-doped tin oxide (FTO), which strengthens adhesion and reduces interfacial recombination centers.
“IOT promotes a gradient oxygen distribution within CdS by exploiting the competition between oxygen and sulfur species. This increases the effective band gap, thereby reducing parasitic light loss,” the scientists said, noting that the The CdS band gap was increased from 2.19 eV to 2.26 eV, which reduced the parasitic absorption of shortwave light and increased the photocurrent.
The cell was built with the glass FTO substrate, the CdS ETL, the Sb2O3 absorber, a lead sulfide (Pbs) layer and a carbon contact.
Tested under standard lighting conditions, the device achieved an efficiency of 9.0%, an open-circuit voltage of 0.4908 V, a short-circuit current density of 26.88 mA/cm2 and a fill factor of 68.19%.
“The cell showed remarkable stability without encapsulation, maintaining performance for 8 months in ambient air and retaining 70% of its initial efficiency after 1,000 hours of severe humid heat testing, significantly outperforming conventional Spiro-OMeTAD/Au-based devices,” said Chen.
The cell was described in “9% certified efficiency record for carbon-based Sb2 (S,Se)3 solar cells enabled by gradient oxidized treatment of CdS electron transport layer”, published in Advanced functional materials.
“Our study provides extensive experimental evidence, using Raman, transmission, and XPS depth profiling, that the IOT creates a longitudinal oxygen-sulfur gradient within the CdS film, with the highest oxygen concentration at the critical FTO/CdS interface,” Chen concluded. “Through advanced characterization and modeling, the study quantitatively demonstrates that optimal interfacial oxygen doping significantly enhances the adhesion energy between CdS and FTO, leading to superior carrier transport and reduced recombination.”
In July 2024, another international research team outlined a new Sb2S3 solar cell design that can reportedly result in 30% higher efficiency compared to existing Sb2S3 concepts for solar cells.
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