An ionic liquid assisted in-situ growth of large-area and high-crystal-quality perovskite single-crystal thin films

Min Liao^{¹^,^§}, Zhaojin Wang^{¹^,^§}, Chengwei Shan^{¹^,^§}, Dengfeng Luo^{¹^,²}, Zhongyuan Guan^¹, Qingqian Wang^{¹^,⁴}, Hongmei Zhu^¹, Zhulu Song^¹, Dan Wu^³(), Aung Ko Ko Kyaw^¹

(), Kai Wang^¹

()

1Department of Electronic and Electrical Engineering, Southern University of Science and Technology, Shenzhen 518055, China

2Peng Cheng Laboratory, Shenzhen 518055, China

3College of New Materials and New Energies, Shenzhen Technology University, Shenzhen 518118, China

4Institute of Physics, Henan Academy of Sciences, Zhengzhou 450046, China

^§ Min Liao, Zhaojin Wang, and Chengwei Shan contributed equally to this work.

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After introducing the cesium(I) bis(trifluoromethanesulfonyl)imide (CsTFSI) ionic liquid, the Cs⁺ ions enter the MAPbBr₃ lattice, reducing the formation energy, and the coordination between the lone pair electrons of O in TFSI^– and the empty orbital of Pb in MAPbBr₃ passivates the dangling bond defects of Pb, facilitating the formation of MAPbBr₃ single-crystal thin films (SCTFs) with high-crystal-quality. Moreover, the strong interaction between TFSI^– and the substrate can enhance wettability and reduce the contact angle, thereby promoting faster solute diffusion and enabling the growth of larger-area MAPbBr₃ SCTFs.

Abstract

In-situ growth of perovskite single-crystal thin films (PeSCTFs) on the transport layer is crucial for achieving high-performance perovskite optoelectronic devices, such as solar cells, light emitting diodes, photodetectors, etc. However, in-situ growing PeSCTF on the transport layer with large-area, high-crystal-quality, and low-trap-density simultaneously remains challenging. This work proposes a method for in-situ growing large-area and low-trap-density MAPbBr₃ SCTFs on the poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) transport layer with the assistance of cesium(I) bis(trifluoromethanesulfonyl)imide (CsTFSI) ionic liquid. After introducing the CsTFSI ionic liquid, the Cs⁺ ions enter the MAPbBr₃ lattice, reducing the formation energy, and the coordination between the lone pair electrons of O in TFSI^– and the empty orbital of Pb in MAPbBr₃ passivates the dangling bond defects of Pb, facilitating the formation of MAPbBr₃ SCTFs with high-crystal-quality. Moreover, the strong interaction between TFSI^– and the substrate can enhance wettability and reduce the contact angle, thereby promoting faster solute diffusion and enabling the growth of larger-area MAPbBr₃ SCTFs. Therefore, compared to the sample without CsTFSI addition, the MAPbBr₃ SCTFs with CsTFSI addition exhibit better thermal stability, larger area (increased from 1.79 to 19.68 mm², approximately a 10-fold increase), lower trap density (decreased from 6.86 × 10¹² to 5.39 × 10¹² cm^–3), and higher carrier mobility (increased from 0.72 to 0.84 cm²∙V^–1∙s^–1). Moreover, the performance of the photodetector with CsTFSI, including responsivity, external quantum efficiency (EQE), detectivity, and response speed, also increased significantly. This work provides an effective method for the in-situ growth of PeSCTFs with large-area, high-crystal-quality, and low-trap-density simultaneously on the transport layer.

Keywords

perovskite single-crystal thin films ionic liquid in-situ growth photodetector

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References

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