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The simulated tandem cell integrates a hole transport layer made of kesterite and lead-free perovskite materials. Its creators claim that the combined device performs more than the individual cells it integrates.
An international group of researchers has designed a perovskite-perovskite tandem solar cell that integrates a hole transport layer (HTL) made of kesterite (CZTSe).
Kesterite is one of the most promising light-absorbing materials for possible use in low-cost thin film solar cells. Kesterite includes common elements such as copper, tin, zinc and selenium. Unlike CIGS compounds, no supply bottlenecks are anticipated in the future. However, kesterite is still less efficient than CIGS in mass production. The world record for this type of cell is 12.6%, achieved in large surface devices by the Japanese thin film producer Solar Frontier in 2013.
“Copper-based materials offer excellent chemical stability, conductivity, and hole transport mobility, making them ideal for HTL in perovskite devices,” the scientists say. “In addition, CZTSe is terrestrial, non-toxic, inorganic and environmentally friendly, with a high absorption coefficient of around 104 cm-1, an optimized direct energy band gap of 0.95 eV and outstanding stability” .
The scientists used the SCAPS-1D solar cell capacitance software, developed by Ghent University, to simulate the novel cell configuration. For the upper cell they used a broadband perovskite material known as MAGeI3, while for the lower device they considered a narrow band perovskite known as FAMASnGeI3. Both materials are lead-free mixed cation perovskites.
The simulated tandem device was constructed with a fluorine-doped tin oxide (FTO) substrate, a strontium titanate (STO)-based electron transport layer (ETL), the MAGeI3 absorber, a tunnel junction, the FAMASnGeI3 absorber, the HTL CZTSe and a gold (Au) metal contact. The ideal thickness of the MAGeI3 and FAMASnGeI3 absorbers was 450 nm and 400 nm, respectively. That of the tunnel junction was 4 nm.
The simulation showed that the tandem device has the potential to achieve a power conversion efficiency of 23.32%, an open circuit voltage of 0.970 V, a short circuit density of 28.46 mAcm-2, and a fill factor of 84.43%.
“It was observed that the efficiency of the cell depends on the thickness of the tunnel junction and the selection of the work function of the face contact,” the academics stated. “Therefore, it can be determined that the mixed cationic perovskite/Pb-free CZTSe tandem device performs better than the single junction device.”
The novel cell concept can be found in the study “ Enhancing Solar Cell Efficiency through Tandem Structures Utilizing Lead-Free Mixed Cation Perovskites and CZTSe Absorber Layers ” and CZTSe absorbing layers), published in Chemical Physics Impact . The research team consisted of scientists from Princess Nourah bint Abdulrahman University, Al-Baha University and Taibah University in Saudi Arabia, as well as Faisalabad University in Pakistan and Punjab University. Academics from the Ettore Majorana University of Astronomy in Catania (Italy) also participated. |
