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The Chinese Academy of Sciences (CAS) has used a new selenization method to build a kesterite solar cell with better charge transport and power conversion efficiency. The National Metrology and Testing Center of the Photovoltaic Industry of China (NPVM) has certified the results.
Researchers led by the Chinese Academy of Sciences (CAS) have designed a kesterite (CZTSSe) solar cell using a new selenization approach that reportedly facilitates the direct and rapid formation of the kesterite phase, thereby improving charge transport in the absorbent film.
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 devices by the Japanese thin film producer Solar Frontier in 2013.
The scientists said they implemented a dual-temperature zone selenization approach to realize a synergistic solid-liquid/solid-gas selenization reaction strategy.
“The introduction of a large amount of liquid selenium (Se) has facilitated a solid-liquid reaction pathway, while the high chemical potential of Se has promoted the direct and rapid formation of the Kesterite phase,” they explained. “In the later phase, a synergistic regulation of Se condensation and volatilization has led to better crystal growth and greater removal of organic residues.”
They also explained that the strategy requires predepositing a sufficient amount of liquid selenium into the precursor film to facilitate liquid phase-assisted phase evolution and crystal growth. The following synergistic control of selenium volatilization aims to balance film crystallization and organic removal.
The research team constructed the cell with an absorber based on Kesterite films with reduced bulk and interface defects, a cadmium sulfide (CdS) buffer layer, a zinc oxide (i-ZnO) window layer, an indium tin oxide (ITO) layer and an anti-reflective coating (ARC) based on magnesium fluoride (MgF2). The device has an aperture area of ??0.2627 cm2 and a designated illuminated area of ??1.066 cm2.
Tested under standard lighting conditions, the cell achieved a maximum power conversion efficiency of 13.6%. The National Metrology and Testing Center of the Photovoltaic Industry of China (NPVM) has certified an efficiency of 13.44% for the device.
When tested on a large surface area device of 1.09 cm2, the cell technology achieved a certified efficiency of 12.1%.
The scientists presented the new cell design in the study “ Controlling Selenization Equilibrium Enables High-Quality Kesterite Absorbers for Efficient Solar Cells ,” published in Nature Communications . .
Looking to the future, they aim to develop novel strategies to control solid-gas/solid-liquid reactions in kesterite materials. “Taken together, our work represents a positive effort to precisely control the selenization reaction process and multiphase reaction pathways,” they conclude. |
