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Indian researchers have proposed building tandem solar cells based on a CIGS top cell and a bottom cell with a single-walled carbon nanotube (SWCNT) absorber. SWCNTs were previously used in solar research as an alternative to conventional metal grid contacts or hole transport layers (HTL), as they combine optoelectronic properties, flexibility, chemical stability and simple transfer protocols.
Scientists led by the MMM University of Technology in Gorakhpur, India, have developed a tandem solar cell based on an upper copper-indium-gallium-diselenide (CIGS) cell and a lower one relying on a single-walled carbon nanotube absorber. (SWCNT).
“To the best of our knowledge, this is the first attempt to build tandem solar cells based on CIGS and SWCNT,” Alok Patel, corresponding author of the research, told pv magazine . “In the upper cell we use an ultra-thin WSeTe, a compound belonging to the group of transition metal chalcogenides, as a buffer layer to reduce absorption loss. “In the bottom cell, we use a buffer layer of zirconium disulfide (ZrS2), which also belongs to the group of transition metal dicalkogenides.”
SWCNTs have previously been used in solar research as an alternative to conventional metal grid contacts or hole transport layers (HTLs), as they are said to combine optoelectronic properties, flexibility, chemical stability and simple transfer protocols to cover large surfaces.
In the study “ Design and performance investigation of CIGS/SWCNT tandem solar cell for efficiency improvement ,” published in Optics Communication , the research group explains who numerically optimized the solar cell using the SCAPS-1D solar cell capacitance software, developed by Ghent University, to simulate the novel thin film cell design.
The academics designed the top cell with a CIGS as an absorber, a WSeTe-based electron transport layer (ETL), an aluminum contact, and a zinc oxide (i-ZnO) window layer. As for the bottom cell, it was planned to be based on the SWCNT absorber, the ZrS2 buffer layer and an indium tin oxide (ITO) window layer. The bottom cell has a bandgap of 1.24 eV and the top device 1.18 eV, which the scientists say ensures that the bottom device absorbs the higher wavelengths transferred from the top cell.
The CGIS cell with a 2,000 nm thick absorber achieved a maximum power conversion efficiency of 23.69%, an open circuit voltage of 0.7437 V, a short circuit current density of 40.25 mA/cm2, and a fill factor of 79.15%. The SWCNT device with a 2,000 nm thick absorber achieved a maximum power conversion efficiency of 17.10%, an open circuit voltage of 0.5653 V, a short circuit current density of 40.36 mA/cm2, and a fill factor of 74.96%.
For the tandem cell, the scientists used a version of the CIGS cell with an efficiency of 22.82% and a sample of the SWCNT device with an efficiency of 16.05%, bringing their combined efficiency to 38.91%. . “This research work can help fabricate efficient tandem photovoltaic cells based on CIGS and SWCNT materials,” the researchers say. |
