Two‐Step Cooling Strategy for Synergistic Control of Cu_Zn and Sn_Zn Defects Enabling 12.87% Efficiency (Ag,Cu)₂ZnSn(S,Se)₄ Solar Cells

Abstract

Abundant intrinsic defects and defect clusters in Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells lead to severe nonradiative recombination and limited photoelectric performance. Therefore, developing effective method to suppress the detrimental defects is the key to achieve high-efficiency solar cell. Herein, a convenient two-step cooling strategy in selenization process is reported to suppress the Cu Zn and Sn Zn defects and defect clusters synergistically. The results show that rapid cooling during section from selenization temperature to turning temperature can inhibit the volatilization of Sn and restrain the corresponding Sn-related defects, while slow cooling during the subsequent temperature section can reduce the degree of Cu-Zn disorder. Benefitting from the synergistic effect of two-step cooling, a significantly lowered concentration of Sn Zn and Cu Zn defect and their defect clusters [2Cu Zn +Sn Zn ] in absorber is observed, meanwhile, a reduced band tailing effect and promoted carrier collection efficiency of the photovoltaic device is obtained. Finally, a device with improved open-circuit voltage (V oc ) of 505.5 mV and efficiency of 12.87% is achieved. This study demonstrates the impact of cooling process on defects controlling for the first time and provides a simple and effective new strategy for intrinsic defect control, which may be universal in other inorganic thin film solar cells.

9.2% Efficient Cu2ZnSn(S,Se)4 Thin Film Solar Cell Based on Inkjet-Printed Absorber

“…The photoluminescence (PL) spectrum measured at 137 K shows a main peak centered at 1.090 eV (black line in the inset of Figure b), which is only 5 meV lower than the band gap obtained from EQE. Wu et al reported a decrease of the difference between the PL emission and the optical band gap from 20 to 2 meV by developing a two-step cooling strategy during selenization to suppress the defect states . The energy difference between the PL emission and the optical band gap in our finding is quite small, suggesting that there is a low band tail state density in the inkjet-printed CZTSSe absorber.…”

“…Wu et al reported a decrease of the difference between the PL emission and the optical band gap from 20 to 2 meV by developing a two-step cooling strategy during selenization to suppress the defect states. 30 The energy difference between the PL emission and the optical band gap in our finding is quite small, suggesting that there is a low band tail state density in the inkjet-printed CZTSSe absorber. In summary, we demonstrate that compact and crack-free CZTSSe thin films with high crystallinity and a low band tail state density can be achieved by inkjet printing of the preoptimized precursor ink under ambient condition.…”

Progress and prospectives of solution-processed kesterite absorbers for photovoltaic applications

“…140 In 2022, an efficiency of 12.87% was achieved using a two-step cooling strategy, which can suppress the Cu Zn and Sn Zn defects and defect clusters synergistically. 141…”

“…140 In 2022, an efficiency of 12.87% was achieved using a two-step cooling strategy, which can suppress the Cu Zn and Sn Zn defects and defect clusters synergistically. 141 Unlike amine-thiol, DMSO and other solvents, the fabrication of CZTSSe solars by EGME solvent is not only insensitive to oxygen and water in the air but also does not show decomposition or uneven morphology. Moreover, the precursor solution configuration process, including the spin coating process and annealing process by this solvent system, can be operated in the air.…”

Crown Ether-Assisted Colloidal ZnO Window Layer Engineering for Efficient Kesterite (Ag,Cu)2ZnSn(S,Se)4 Solar Cells

“…In the current research stage, greater focus has been paid to the CZTSSe absorber layer itself. Researchers have continuously explored to improve the CZTSSe crystal quality through bulk phase regulation, , element doping, , selenization/sulfurization modification, , solvent engineering, , and so on. Over 14% efficiency has been achieved for kesterite solar cells by regulating the phase evolution kinetics of Ag-alloyed CZTSSe in a positive pressure .…”