Estonian researchers used the CSS coating technology for the first time to manufacture solar cells based on antimony trisulfide (Sb2S3). The resulting devices have so far shown limited power conversion efficiency, but the researchers claim that the new process paves the way for the future development of soil-abundant inorganic photovoltaic materials.
Sb2S3 is a promising candidate for the photovoltaic community because it contains abundant earth and environmentally friendly structural components, as well as appropriate optoelectronic properties such as a desirable bandgap of about 1.7 eV and a large absorption coefficient of about 105 cm-1, and long-term stability. The highest efficiency of such photovoltaic devices is currently 8%
“For the first time in our work, a concept solar cell with CSS Bi2S3 presented and provided an in-depth analysis of the relationship between grain structure, interface recombination and device performance,” said Mykhailo Koltsov, lead author of the study. pv magazine. “Using low-temperature dependence of photoluminescence (PL), we presented for the first time new and complementary insights into the potential defects and recombination mechanisms of green and earth-abundant Bi.2S3 PV material.”
The scientists initially developed several Bi2S3 absorber films deposited on different substrates. They then used a scanning electron microscope (SEM) to study their properties and morphology to identify those with optimal growth.
With the best Bi2S3 absorbing film, the researchers built a cell based on a substrate made of glass and fluorine-doped tin oxide (FTO), an electron transfer layer (ETL) using either titanium oxide (TiO2), Sb.2S3 the absorber itself and the gold (Au) metal contacts. The Bi2S3 absorbent was deposited at 450C. They also built a similar device based on cadmium sulfide (CdS)-based ETL.
The first cell achieved a power conversion efficiency of 0.1%, an open circuit voltage of 10 mV, a short circuit current of 3.5 mA/cm2, and a fill factor of 23.0. The second device achieved an efficiency of 0.3%, an open circuit voltage of 190 mV, a short circuit current of 4.6 mA/cm2, and a fill factor of 32.0.
“Both device assemblies treated with Bi2S3 at CSS substrate temperatures below 400 ◦C generally have zero efficiencies,” the researchers noted. “A source temperature of 550 C and a substrate temperature of 400-450 C were identified as optimal temperatures that allowed reasonable deposition rates and the production of uniform Bi2S3 films.”
According to Koltsov, the development of Bi2S3 PV technology would mean lower processing temperatures and reduced time compared to state-of-the-art thin film industry technologies, especially the use of thinner absorbers deposited by one-step processes.
“This significantly reduces manufacturing power requirements and ensures lower CO emissions2 footprint and environmental impact,” he continued. “Environmental impacts are also reduced by the fact that there are no toxic or dangerous substances in the manufacturing process.”
The potential for reducing the cost of power generation can be understood by considering compatibility with the established thin film CdTe technology. Existing infrastructure could be used to lower the cost per watt of the CdTe module to achieve equivalent efficiency.
“Cadmium and telluride are currently around $3.3/kg and $70/kg, respectively,” he said. “Bismuth and sulfur—the two compounds that make up Bi2S3 P – currently costs $8.6/kg and up to 0.5/kg. In addition, Bi2S3 the thickness of the absorber is less than 1 μm, while the thickness of the CdTe absorber is usually 2 μm.
Koltsov believes that Bi2S3 the technology has the potential to lower the price of solar electricity by aiming for production costs below €0.20 ($0.224)/W.