en.Wedoany.com Reported - A research team from Shandong Police College in China has developed a novel soft chemical treatment method aimed at improving the efficiency of copper-zinc-tin-selenide (CZTSe) solar cells.
The research team stated that the mechanism of alkali metal treatment for CZTSe solar cells still requires in-depth investigation. Sodium or potassium treatment can significantly enhance the performance of thin-film solar cells, exerting important effects on the device by passivating the absorber layer surface, reducing grain boundary defects, optimizing crystal quality, and increasing carrier concentration.
This method uses a potassium fluoride (KF) solution to treat the absorber layer. The research team fabricated CZTSe cells on soda-lime glass (SLG) substrates coated with a molybdenum (Mo) back contact layer. Copper (Cu), zinc (Zn), and tin (Sn) precursor layers were deposited via magnetron sputtering and adjusted to a copper-poor, zinc-rich composition. Subsequently, the precursors were immersed in KF solutions with concentrations of 0, 3, 6, or 9 mmol/L for 20 minutes and dried at 80°C for 20 minutes.
The samples were then selenized in a selenium atmosphere at 550°C to form the CZTSe absorber layer. The cells were completed by depositing a 50 nm thick cadmium sulfide (CdS) buffer layer, along with intrinsic zinc oxide (i-ZnO), aluminum-doped zinc oxide (AZO), and nickel/aluminum (Ni/Al) front contact electrodes. The final device structure was SLG/Mo/CZTSe/CdS/i-ZnO/AZO/Ni:Al.
After fabrication, the team characterized the devices using scanning electron microscopy, current density-voltage (J-V) measurements, external quantum efficiency (EQE) measurements, and capacitance-voltage (C-V) measurements. The results showed that CZTSe performance improved when the KF concentration was increased to an optimal value of 6 mmol/L, but further increase to 9 mmol/L led to performance degradation.
The device treated with 6 mmol/L KF achieved an efficiency of 8.04%, an open-circuit voltage of 0.392 V, a short-circuit current density of 34.3 mA/cm², and a fill factor of 59.7%. In comparison, the reference device without KF treatment had values of 6.59%, 0.332 V, 33.7 mA/cm², and 58.8%, respectively.
To investigate the underlying mechanism, the team used the wxAMPS simulation software to study the impact of interface defects and carrier density on device performance. By varying parameters, they found that reducing interface defects significantly improved efficiency and open-circuit voltage by suppressing carrier recombination, while increasing carrier density reduced performance.
The research team concluded that potassium promotes CZTSe grain growth during high-temperature selenization and reduces the formation of voids during film growth. The soft KF treatment also provides an excess potassium source, effectively suppressing surface decomposition, particularly by reducing tin loss through decreased desorption of SnSe(g), thereby improving the CdS/CZTSe interface.
The findings were published in the journal Materials Today Communications under the title "Potassium processing interface engineering for carrier regulation of efficient CZTSe solar cells."
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