Tandem solar cell based on cadmium telluride, iron disilicide promises 43.9% efficiency

Researchers at the University of Rajshahi in Bangladesh have simulated a dual-junction tandem solar cell based on two PV devices reyling on absorbers made of cadmium telluride (CdTe) and iron disilicide (FeSi2).

Inorganic FeSi2-based solar cells have recently drawn a lot of attention from the scientific community as these devices offer superior thermal stability and good optoelectronic properties compared to conventional solar cells. Furthermore, Fe and Si used to form FeSi₂ are abundant in nature.

The scientists explained that their tandem cell takes advantage of combining the larger bandgap of the top CdTe cell and the smaller bandgap of the bottom FeSi2 cell. “The top cell transforms photons with elevated energy efficiently while minimizing thermalization losses and transmitting the solar spectrum in the close-infrared region light to the lower cell,” they highlighted. “In order to improve light absorption, it is crucial to reduce the undesired losses at the junction resulting from Fresnel surface reflection.”

The scientists used the SCAPS-1D solar cell capacitance software, developed by the University of Ghent, to simulate the novel cell configuration. They assumed the top cell to be built with an n-type cadmium sulfide (CdS) window layer, the CdTe absorber, and a back surface field (BSF) based on molybdenum disulfide (MoS₂). 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 considered parameters such as energy bandgap, diffusion length, and doping concentration. “CdTe has featured a 1.5 eV bandgap and a 4.28 eV electron affinity, while the bandgap and electron affinity of FeSi₂ are 0.87 eV and 4.16 eV, respectively,” it specified. “An optimal, slender tunnel junction connecting the upper and lower cells with monolithic architecture has been assumed for the electrical linkage.”

The numerical analysis showed that the top CdTe cell may potentially achieve a power conversion efficiency of 26.13%, while the FeSi₂ bottom cell may reach up to 35.25%. It also demonstrated that the tandem device may 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 affirmed.

The cell was described in the study “Design and optimization of a high efficiency CdTe–FeSi₂ based double-junction two-terminal tandem solar cell,” published in Heliyon.