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The solar cell was treated with multi-elemental alloy, which supposedly helped eliminate defects in the kesterite absorber, thus increasing the efficiency of the cell. Chinas National Photovoltaic Industry Testing and Measurement Center confirmed the results.
A group of researchers led by the Chinese Academy of Sciences (CAS) has manufactured a kesterite (CZTSSe) solar cell that achieves a maximum power conversion efficiency of 14.6% and a certified efficiency of 14.2%.
“The performance of kesterite solar cells is mainly limited by defect-induced charge loss,” Qingbo Meng, corresponding author of the research, told pv magazine . “We believe that a more comprehensive understanding of the mechanism of defect formation in this material system and more effective control of the defect formation process will allow us to make more progress in the future.”
Kesterite is one of the most promising light-absorbing materials for possible use in low-cost thin film solar cells. Kesterites include 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 area devices by the Japanese thin film producer Solar Frontier in 2013.
The Chinese research team used what it described as a kinetics-based approach to suppress the formation of deep defects in the CZTSSe absorber. It involved using multi-element alloying to remove tin (Sn) and zinc (Zn) defects in the final CZTSSe material by adding silver (Ag) and cadmium (Cd) through the precursor solution and germanium (Ge) from the back interface. “The elemental alloying has facilitated the exchange of Zn/Sn and Zn/Cu, leading to accelerated formation of the ordered kesterite phase,” the scientists explain.
They built the solar cell with a molybdenum (Mo)-coated soda-lime glass (SLG) substrate, the CZTSSe absorber, a cadmium sulfide (CdS) buffer layer, a zinc oxide (ZnO) window layer, and a indium tin oxide (ITO), and an anti-reflective coating based on magnesium fluoride (MgF2).
Tested under standard lighting conditions, the device achieved a power conversion efficiency of 14.6%, an open circuit voltage of 0.55 V, a short circuit current of 36.6 mA cm-2 and a fill factor of 72.4%. The National Center for Measurements and Testing of the Photovoltaic Industry of China certified that the cell reached an efficiency of 14.2%.
“The main discrepancy between the certified result and that of our laboratory, i.e. the filling factor, is attributed to the influence of the MgF2 antireflection layer on the electrical contact of the probe,” the academics explain. “These results indicate that the multilevel alloy can more effectively regulate the reaction kinetics to suppress deep defects in CZTSSe and thus create more favorable moderate reaction conditions to meet the requirements of large-scale and low-cost industrial manufacturing.”
The new solar cell concept was presented in the article “ Multinary alloying for facilitated cation exchange and suppressed defect formation in kesterite solar cells with above 14% certified efficiency ” of kesterite with a certified efficiency greater than 14%.), recently published in nature energy . “These insights and the data-driven analysis method presented here also provide further avenues for identifying and regulating defects in photovoltaic materials,” the research team concludes. |
