Nano-Micro Letters: Synergistically stabilized buried interface via fluorine and sulfonic acid groups to obtain perovskite cells with over 24% efficiency based on a two-step method

• Interface defects and unsatisfactory interface energy band matching are the main causes of non-radiative recombination at the interface. In addition, the poor crystallinity of the lead iodide thin film and the perovskite thin film limits the further improvement of the photovoltaic performance of the device prepared by the two-step method. In view of this, a buried interface stabilization strategy based on the synergistic effect of fluorine (F) and sulfonyl (S=O) functional groups is summarized.

• Fluorine (F) and sulfonyl (S=O) functional groups can realize various chemical bonds with perovskite components such as hydrogen bonds, coordination bonds, and ionic bonds, which enhance the interface contact and defect passivation effects. The chemical interaction between modified molecules and perovskite and SnO2 is continuously enhanced with the increase of S=O and F numbers. The defect passivation effect is positively correlated with the chemical interaction strength. Perovskite crystallization kinetics are regulated by a balance between the strength of chemical interactions and the wettability of the substrate. All non-halogen anions perform better in terms of crystallization optimization, energy band tuning, and defect passivation than Cl-.

  
  

  Correlations between molecular structure, defect passivation, interfacial band alignment, perovskite crystallization, and device performance are established. The device modified by KFSI achieved an efficiency of 24.17%.

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• Fig. 1aMolecular structures of potassium salts used for modifying buried interface and schematic illustration of the interaction of modifiers and functional layers.bSn 3d andcO 1s XPS spectra of the control and modified SnO2 layers.dFTIR spectra of pure KMS, KTFSI and KFSI and the SnO2films without and with KMS, KTFSI and KFSI.eXPS spectra of the control and modified perovskite films.fFTIR spectra of the PbI2films with or without KMS, KTFSI and KFSI. XRD patterns of thegPbI2 films andhperovskite films deposited on SnO2ETLs without or with KCl, KMS, KTFSI and KFSI.
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• Fig. 2a,bTop-view andccross-sectional SEM images of the control and modified perovskite films.
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• Fig. 3aUV-vis absorption spectra of the perovskite films with or without modifiers.b,dSSPL andc,eTRPL spectra of the perovskite films prepared on non-conductive glass without and with modifiers by measuring from theb,cglass side ord, eperovskite side.fPL mapping images of the perovskite films deposited on non-conductive glass without and with modifiersgDark I–V curves of the electron-only devices.

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• Fig. 4aSSPL andbTRPL spectra of the perovskite films deposited on SnO2 films without and with modifiers. PL mapping images of the perovskite films prepared on thecbare SnO2 and SnO2 modified bydKCl,eKMS,fKFSI andgKTFSI.hMott–Schottky analysis,iVOC as a function of light intensities for the control and modified PSCs,jTPC andkTPVlNyquist plots of the control and modified devices measured at a bias of 0.8 V in the frequency range of 1 MHz to 0.01 Hz in the dark. An enlarged view of the high-frequency region is shown in the inset.

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• Fig. 5aStatistical distribution of the PCEs of the PSCs based on the SnO2 films without and with KCl, KMS, KTFSI and KFSI. The statistical data were obtained from 20 individual cells for each kind of device.bJ–Vcurves andcEQE spectra of the best-performing devices based on bare SnO2 film and KCl, KMS, KTFSI and KFSI modified SnO2 films. J–Vcurves were measured under simulated AM 1.5G one sun illumination of 100 mW/cm2.dSteady-state current density andePCE versus time for the best-performing devices employing pristine and modified SnO2 films measured at the maximum power point.fJ-V curves of the KFSI-modified champion PSCs with PEAI posttreatment. PCE evolution of the unencapsulated control and modifiedgunder 25%-30% relative humidity at room temperature in the dark,hat 60 ℃ in the dark in the nitrogen-filled glovebox. Error bars represent the standard deviation of five devices.

• References

  
  Cheng Gong, Haiyun Li, Cong Zhang, Qixin Zhuang, Zhiyuan Xu, Huaxin Wang, Ru Li, Hua Yang, Jiangzhao Chen,* and Zhigang Zang*. Stabilizing buried interface via synergistic effect of fluorine and sulfonyl functional groups toward efficient and stable perovskite solar cells. Nano-Micro Letters.15,1 (2022).
  https://doi.org/10.1007/s40820-022-00992-5
  https://link.springer.com/10.1007/s40820-022-00992-5