An international research team used the ultrasonic jet pyrolysis (USP) method to fabricate an antimony trisulfide PV cell with high power conversion efficiency and remarkable average visible transmittance. The active surface area of the cell is 7.06 mm2.
“HTMs were systematized and developed in the research group of Kaunas University of Technology professor Vytautas Getautis,” said researcher Ilona Oja Acik. pv magazine.
“Sb2S3 is a promising candidate for the photovoltaic community due to its abundance of 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 (about 10).5 cm-1) and long-term stability,” the researchers explained, noting that the highest efficiency of such PV devices is now 8%. “Overall efficiency is quite limited by open-circuit voltage deficiencies (VO.C), due to self-trapping of carriers due to lattice deformations and/or internal defects, which sets the maximum achievable VO.C to 0.8 V.”
Using the ultrasonic jet pyrolysis (USP) method, the research team built a cell with an active surface area of 7.06 mm.2. The device is based on a substrate made of glass and fluorine-doped tin oxide (FTO), titanium oxide (TiO2) electron transfer layer (ETL), Sb.2S3 absorber, fluorene-based hole transport materials (HTMs) with terminated thiophene units, and gold (Au) metal contacts.
“Sb2S3 The solar cells with the new HTMs are fabricated in a standard superstrate configuration, where USP coats the ETL and absorber, while the HTMs are spin-coated, followed by thermal evaporation of the Au,” they explained. “The deposited Sb2S3 films were annealed at approximately 250–260 C for 5 min under nitrogen.”
The built master device has a power conversion efficiency of 4.94%, an open circuit voltage of 0.68 V, and a short circuit current of 13.7 mA/cm2, and a fill factor of 0.53. This cell uses fluorene-based molecules known as V1385. The researchers said this could ensure a plausible fabrication of Sb2S3 solar cells with an efficiency of almost 5% much cheaper.
In comparison, Sb2S3 solar cells built from conventional hole transporting layers (HTL). the polymer Regioregular poly(3-hexylthiophene) (P3HT) has so far achieved an efficiency of up to 4.7% at the research level.
“However, they have had lower transparency (26%) due to parasitic absorption losses in P3HT,” the researchers said. “New cost-effective and transparent fluorene-based thiophene-terminated hole transport materials are demonstrated for the first time in semitransparent Sb2S3 solar cells with a power conversion efficiency of 4.5–4.9 percent and an average visible transmittance of 30–33 percent (without metal) in the 400–800 nm range.
They introduced the solar cell “4.9% Effective Sb2S3 Solar cells from semitransparent absorbers with fluorene-based thiophene-terminated hole conductors”, published recently ACS Publications.