A research group from Spain's Universitat Politècnica de Catalunya (UPC) has fabricated a transparent solar cell based on a light absorber made of amorphous hydrogenated silicon carbide (a-Si1-xCx:H) thin films.
“Our cell shows an outstanding transparency of over 50% for inorganic transparent photovoltaics,” the research's lead author, Gerard Masmitjà, told pv magazine, noting that solar cells based on amorphous silicon have regained interest in recent years as a promising option for implementing highly reliable transparent devices. “We demonstrated that tuning the a-Si1-xCx:H bandgap is possible, which is not only advantageous for transparent solar cells, but could also have applications in tandem devices.”
The 0.5 cm × 0.5 cm solar cell was also built with a substrate made of commercial glass coated with fluorine-doped tin oxide (FTO).
The 40-45 nm a-Si1-xCx:H absorber was deposited on a borosilicate glass substrate by a plasma-enhanced chemical vapor deposition (PECVD) with different SiH4/CH4 ratios, while a 45 nm aluminum-doped zinc oxide (AZO) hole transport layer was deposited by atomic layer deposition (ALD), which was also utilized to deposit a a 12 nm thick hole-selective contact of vanadium oxide (V2Ox).
For the electron transport layer (ETL), the research team used a wide-bandgap phosphorus-doped a-Si1-xCx:H film. Diethylzinc (DEZ), Trimethylaluminum (TMA) and DI-H2O were used as zinc, aluminum and oxidant precursors.
The scientists analyzed the microstructure of the a-Si1-xCx:H solar cell through scanning transmission electron microscope (STEM) images recorded from the JEOL bright-field (BF) and high-angle annular dark-field (HAADF) detectors. They used a JEOL F200 TEM ColdFEG operated at 200 kV, with samples being placed in a JEOL beryllium double-tilt holder for energy dispersive X-ray spectroscopy (EDS).
The best solar cell fabricated with the proposed architecture achieved a power conversion efficiency of 2.6%, an open-circuit voltage of of 748 mV, a short-circuit current of 5.2 mAcm2, and a fill factor of 68%. “Higher carbon content in a-Si1-xCx:H improves efficiency under indoor light conditions,” Masmitjà explained.
Some of the devices also showed average photopic transmittance (APT) values ranging 50 % and 70 %. This metric define transparency for the human eye rather than providing a simple arithmetic average. It recently became a critical benchmark for applications like solar windows and semi-transparent PV cells.
“This demonstrates that truly transparent, non-organic solar cells can be achieved while maintaining remarkable power conversion efficiencies,” the researchers said. “Beyond transparency, carbon incorporation also enhances the suitability of these devices for indoor applications, as their efficiency is better maintained under low-light conditions.”
The cell was described in “Transparent solar cells based on a-Si1-xCx:H alloys: from silicon to carbon-rich absorbers,” published in Renewable Energy.
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