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Researchers in Bangladesh have designed a double junction tandem solar cell with a bottom device based on iron disilicide (FeSi2), an emerging absorbent material known for its high thermal stability and good optoelectronic properties. Their simulation demonstrated the advantage of combining the larger bandgap of the upper cadmium telluride cell and the smaller bandgap of the lower FeSi2 cell.
Researchers at the University of Rajshahi (Bangladesh) have simulated a double-junction tandem solar cell based on two photovoltaic devices that are built on cadmium telluride (CdTe) and iron disilicide (FeSi2) absorbers.
FeSi2-based inorganic solar cells have recently attracted much attention from the scientific community, as these devices offer superior thermal stability and good optoelectronic properties compared to conventional solar cells. Furthermore, the Fe and Si used to form FeSi2 are abundant in nature.
The scientists explained that their tandem cell takes advantage of the combination of the higher bandgap of the CdTe upper cell and the lower bandgap of the lower FeSi2 cell. “The upper cell transforms high-energy photons efficiently, while minimizing thermalization losses and transmitting the solar spectrum in the light of the near-infrared region to the lower cell,” they highlighted. “To improve light absorption, it is crucial to reduce unwanted junction losses resulting from surface Fresnel reflection.”
The scientists used the SCAPS-1D solar cell capacitance software, developed by Ghent University, to simulate the novel cell configuration. They assumed that the upper cell was constructed with an n-type cadmium sulfide (CdS) window layer, the CdTe absorber, and a molybdenum disulfide (MoS2) based back surface field (BSF). The bottom cell was designed with an n-type CdS window layer, the FeSi2 absorber, and a copper tin sulfide (Cu2SnS3) BSF.
In the simulation, the team took into account parameters such as energy bandgap, diffusion length and doping concentration. “CdTe has a bandgap of 1.5 eV and an electronic affinity of 4.28 eV, while the bandgap and electronic affinity of FeSi2 are 0.87 eV and 4.16 eV, respectively,” he specified. “For the electrical connection, an optimal and thin tunnel connection has been used that connects the upper and lower cells with monolithic architecture.”
Numerical analysis showed that the upper CdTe cell can reach a power conversion efficiency of 26.13%, while the lower FeSi2 cell can reach up to 35.25%. It was also shown that the tandem device can achieve an efficiency of 43.91%, an open circuit voltage of 1.928 V, a short circuit current of 25.338 mA/cm2, and a fill factor of 88.88%.
“These results suggest the practical feasibility of fabricating high-performance CdTe-FeSi2 double junction tandem solar cells for efficient solar energy conversion,” the scientists say.
The cell is described in the study “ Design and optimization of a high efficiency CdTe- FeSi2 based double-junction two-terminal tandem solar cell ” high efficiency), published in Heliyon . |
