Researchers at the University of Toledo in the United States fabricated antimony sulfide (Sb2S3) thin film solar cells that achieved a champion power conversion efficiency of 6.89%, which was subsequently improved to 7.69% after a light soaking step.
Investigation of this particular thin film PV absorber has several drivers. “Considering the need for low-cost, earth-abundant, and non-toxic photovoltaic material alternative to other chalcogenides materials like cadmium telluride (CdTe) and copper indium gallium selenide (CIGS), antimony sulfide (Sb2S3) is an emerging material with suitable band gap, high absorption coefficients, excellent optoelectronic properties and robust material stability making it an attractive candidate for single junction solar cells or top-cell in dual junction tandem solar cells,” Alisha Adhikari, corresponding author of the research, told pv magazine.
In the study, “Process Optimization and Light Soaking to Enhance Photovoltaic Performance of Antimony Sulfide Solar Cells,” published in ACS Applied Energy Materials, the research team specified that carrying out hydrothermal growth at 135 C for 225 min, combined with post-annealing at 350 C for 10 min in a tightly controlled process resulted in a device with champion power conversion efficiency of 6.89%, which increased to 7.69% after light soaking.
Adhikari explained that it was expected that after the optimization of the growth process and post-annealing treatments there would be an improvement in device performance of the Sb2S3 solar cells. “However, we were surprised by the extent of improvement in the device performance of Sb2S3 solar cells from 6.89% to 7.69% via light soaking,” she added.
The experimental solar cell stack was as follows: fluorine-doped tin oxide (FTO) substrate with cadmium sulfide (CdS) coating, the Sb2S3 thin film, a spiro-OMeTAD hole transport layer (HTL), and gold (Au) back contacts.
Using atomic force microscopy (AFM) imaging the team observed how surface roughness was flattened after annealing the various samples. “The changes in the grain size and structure correspond to the phase transfer from reddish amorphous metastibnite to black polycrystalline stibnite, which was confirmed by X-ray diffraction (XRD) measurement,” said the team.
The Sb2S3 films reportedly had high absorption coefficients with an absorption band edge of ∼720 nm, corresponding to a bandgap of around 1.7 eV.
“We find that controlling the hydrothermal growth time and post-annealing temperature is crucial to obtaining high-quality Sb2S3 films with the desired film thickness, morphology, and more preferred grain orientations, which leads to improved solar cell performance,” the researchers said.
The light soaking with one-sun irradiance at 70 C had a duration of 120 min. “The improved PCE after light soaking mainly resulted from increased short-circuit current and fill factor,” said Adhikari.
Furthermore, after long-term storage of the light-soaked devices, the efficiency was higher than pristine cells without light soaking. “After 10 months of storage, the cells exhibited a moderate reduction in fill factor, a slight decrease in pen-circuit voltage and negligible change in short-circuit current, retaining more than 95% of their initial efficiencies,” said Adhikari.
Light soaking at an appropriate elevated temperature facilitates the oxidation of spiro-OMeTAD, enhancing its hole extraction and transport properties. “Our findings demonstrate that light soaking is a facile and effective approach to enhance the performance of Sb2S3 solar cells,” concluded the team.
When asked about the future direction of research, Adhikari said that the group is planning to explore stable and cost-effective hole transport layers to further boost the efficiency of Sb2S3 solar cells.
This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: editors@pv-magazine.com.
By submitting this form you agree to pv magazine using your data for the purposes of publishing your comment.
Your personal data will only be disclosed or otherwise transmitted to third parties for the purposes of spam filtering or if this is necessary for technical maintenance of the website. Any other transfer to third parties will not take place unless this is justified on the basis of applicable data protection regulations or if pv magazine is legally obliged to do so.
You may revoke this consent at any time with effect for the future, in which case your personal data will be deleted immediately. Otherwise, your data will be deleted if pv magazine has processed your request or the purpose of data storage is fulfilled.
Further information on data privacy can be found in our Data Protection Policy.