According to foreign media reports, the United States Lehigh University (Lehigh University) researchers in a recently published research report claimed that they developed a new thin-film photovoltaic cell absorbing material, allegedly the average photovoltaic absorption rate of this material is 80%, its external quantum efficiency (EQE) of 190%.
The external quantum efficiency (EQE) is the ratio of the number of electrons collected by a PV cell to the number of incident photons. It defines the ability of a PV cell to convert photons into electrical current. Chinedu Ekuma, one of the lead authors of the study, said in a statement, "In conventional photovoltaic cells, the highest external quantum efficiency (EQE is 100 per cent, which represents the production and collection of one electron for each photon absorbed from sunlight."
In a paper published in the journal Science Advances titled "Chemically tuned intermediate band states of atomically thick CuxGeSe/SnS quantum materials for photovoltaic applications," the researchers explain that the new quantum material could be an ideal match for intermediate band photovoltaic cells (IBSCs).
Such photovoltaic cells have the potential to exceed the Shockley-Quayser limit (S-Q limit) - the maximum theoretical efficiency that can be achieved by a photovoltaic cell with a single p-n junction. It is calculated by examining the amount of electrical energy extracted from each incident photon.
The researchers explain: "The rapid increase in efficiency of this material is largely due to its unique 'intermediate band states', specific energy levels located within the material's electronic structure that make them ideal for photovoltaic conversion. The energy levels of these states are within the optimal subband gap - the energy range in which the material can efficiently absorb sunlight and generate charge carriers."
The new material is a two-dimensional van der Waals (vdW) material, meaning it has a crystalline planar structure held together by ionic bonds. It consists of a heterostructure of germanium (Ge), selenium (Se) and tin sulphide (Sns) with zero-valent copper (Cu) atoms inserted in the material layers.
The CuxGeSe/SnS quantum material has an intermediate energy band gap between 0.78 eV and 1.26 eV. Taking advantage of this, the researchers designed and modelled to simulate a thin-film photovoltaic cell using the material as the active layer.
In this modelling, the PV cell uses an indium tin oxide (ITO) substrate, a zinc oxide (ZnO)-based electron transport layer (ETL), a CuxGeSe/SnS absorber layer, and gold (Au) contacts. The research junior noted, "In our design, atomic-level thicknesses of GeSe and SnS are stacked vertically, contributing to the easy integration of the hybrid structure through van der Waals interactions."
The modelling results show that this PV cell has an external quantum efficiency (EQE) of 110% ~ 190%. The researchers also found that the optical activity of the photovoltaic cell increased in the wavelength range of 600 nm to 1200 nm by measuring the thickness of the absorber.
In their paper, the researchers concluded, "The fast response and increased efficiency of this material strongly suggests the potential of copper-inserted GeSe/SnS as a quantum material for advanced photovoltaic applications, providing a new avenue for improving the efficiency of photovoltaic conversion."
Looking ahead, the researchers say they need to conduct new research to identify a practical way to embed this new material into PV cells. However, they also point out that the experimental techniques used to fabricate these materials are already very advanced.