| Work Detail |
Estonian researchers first applied the short-range sublimation deposition (CSS) technique to fabricate antimony trisulfide (Sb2S3)-based solar cells.
A team of researchers from Tallinn University of Technology (TalTech) in Estonia has developed a solar cell based on antimony trisulfide (Sb2S3) using near-range sublimation (CSS), which is a physical vapor deposition commonly applied to cadmium telluride (CdTe) thin-film solar cells.
Sb2S3 is a promising candidate for the PV community due to the abundance of terrestrial and environmentally friendly constituent elements, together with suitable optoelectronic properties, such as a desirable bandgap of about 1.7 eV, a large absorption coefficient of about 105 cm-1, and long-term stability. Currently, the maximum efficiency of these photovoltaic devices is 8%.
“Our work demonstrated for the first time a proof-of-concept solar cell with CSS Bi2S3 and provided an in-depth analysis of the interrelationship between grain structure, interface recombination, and device performance,” he told pv . magazine the lead author of the research, Mykhailo Koltsov. “Using low-temperature-dependent photoluminescence (PL), we provide the first new and complementary insights into potential defects and recombination mechanisms in green and soil-rich Bi2S3 photovoltaic material.”
The scientists initially developed several Bi2S3 absorber films deposited on various substrates. Using scanning electron microscopy (SEM) they later investigated their properties and morphology, in order to identify those with optimal growth.
Using the best Bi2S3 absorber film, the scientists built a cell based on a glass substrate and fluorine-doped tin oxide (FTO), an electron transport layer (ETL) with titanium oxide (TiO2), the Sb2S3 absorber itself, and gold (Au) metal contacts. The Bi2S3 absorber was deposited at 450 °C. They also built a similar device based on a cadmium sulfide (CdS) 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.
“For both device configurations, processed with Bi2S3 at CSS substrate temperatures below 400 ºC, the efficiencies tend to zero,” the researchers stated. "The source temperature of 550 ºC and the substrate temperature of 400-450 ºC were identified as optimal temperatures that allowed a reasonable deposition rate and the fabrication of uniform Bi2S3 films."
According to Koltsov, the development of Bi2S3 photovoltaic technology would mean lower processing temperatures and reduced processing time compared to more advanced industrial thin-film technologies, particularly the use of thinner absorbers deposited by single-pass processes.
“This represents a significant reduction in energy requirements for manufacturing, ensuring a smaller CO2 footprint and lower environmental impact,” he added. "The environmental impact is also reduced by the absence of toxic or dangerous materials in the manufacturing process."
The potential for reducing energy production costs can be understood by considering compatibility with already established thin-film CdTe technology. Existing infrastructure could be used to reduce the cost per watt of CdTe modules with equivalent efficiency.
“Cadmium and tellurium currently cost about $3.3/kg and $70/kg, respectively,” he explains. “Bismuth and sulfur – the two compounds that make up Bi2S3 P – currently cost $8.6/kg and up to $0.5/kg, respectively. Furthermore, the Bi2S3 absorber is less than 1µm thick, while the CdTe absorber is usually 2µm”.
Koltsov believes that Bi2S3 technology has the potential to reduce the price of photovoltaic electricity, with a target of production costs below 0.20 euros ($0.224)/W.
The solar cell fabrication technique is described in the article “ Development of Bi2S3 thin film solar cells by close-spaced sublimation and analysis of absorber bulk defects via in-depth photoluminescence analysis ”, recently published in Solar Energy Materials and Solar Cells .
Other Taltech researchers presented in April an antimony trisulfide (Sb2S3)-based solar cell that uses fluorene-based hole transport materials (HTMs) with thiophene end units. The champion device built has a power conversion efficiency of 4.94%, an open circuit voltage of 0.68 V, a short circuit current of 13.7 mA/cm2, and a fill factor of 0.53. |
