In perovskite solar cells, the interfaces between the perovskite and charge-transporting layers contain high concentrations of defects (about 100 times that within the perovskite layer), specifically, deep-level defects, which substantially reduce the power conversion efficiency of the devices1,2,3. Recent efforts to reduce these interfacial defects have focused mainly on surface passivation4,5,6. However, passivating the perovskite surface that interfaces with the electron-transporting layer is difficult, because the surface-treatment agents on the electron-transporting layer may dissolve while coating the perovskite thin film. Alternatively, interfacial defects may not be a concern if a coherent interface could be formed between the electron-transporting and perovskite layers. Here we report the formation of an interlayer between a SnO2 electron-transporting layer and a halide perovskite light-absorbing layer, achieved by coupling Cl-bonded SnO2 with a Cl-containing perovskite precursor. This interlayer has atomically coherent features, which enhance charge extraction and transport from the perovskite layer, and fewer interfacial defects. The existence of such a coherent interlayer allowed us to fabricate perovskite solar cells with a power conversion efficiency of 25.8 per cent (certified 25.5 per cent)under standard illumination. Furthermore, unencapsulated devices maintained about 90 per cent of their initial efficiency even after continuous light exposure for 500 hours. Our findings provide guidelines for designing defect-minimizing interfaces between metal halide perovskites and electron-transporting layers.
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The data that support the findings of this study are available from the corresponding authors on reasonable request.
The code used for this study is available from the corresponding authors on reasonable request.
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This work was supported by the Basic Science Research Program (NRF-2018R1A3B1052820) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (MSIP). This work was also supported by the Defense Challengeable Future Technology Program of the Agency for Defense Development, Republic of Korea, a brand project (1.200030.01) of UNIST, and Alchemist Project (2019309101046). We thank UCRF (UNIST central research facilities) for use of equipment and the beamline staff at Pohang Accelerator Laboratory.
The authors declare no competing interests.
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Extended data figures and tables
The black line is the analysis result for the Cl ions on the thin film obtained after spin coating with the SnCl2.2H2O solution dissolved in ethanol and then heat treatment at 190 °C for 1 h. The blue line is the result of Cl−ion analysis on a thin film obtained by spin coating a SnO2 colloid generated by heat treatment at 70 °C for 30 min after dissolving 0.1 mol of SnCl4 in deionised water.
Extended Data Fig. 2 Depth profiles analysed by ToF-SIMS with a PSC fabricated using a commercial SnO2 colloids as electron-transporting layer.
Extended Data Fig. 3 DFT simulation of the formation of the interlayer between the perovskite and SnO2.
a, back side view, b, right side view, and c, left side view of Fig. 1d in (a) 3-dimensional and (b) 2-dimensional shapes. [Pb (black), I (purple), Cl (green), C (brown), N (light blue), H (white), Sn (dark blue), and O (red)].
Extended Data Fig. 4 Theoretical simulation for the formation of an interlayer between Cl-TiO2 and Cl-cPP.
Extended Data Fig. 5 Wavelet transform of correlation between the Fourier-transformed peaks with k-space data for local geometric environments around Sn of SnO2, which was annealed at 120 °C for 1 h using a perovskite precursor without Cl- ions coated on a Cl-bSO electrode.
Extended Data Fig. 6 Simulation of the diffraction peaks by a, FAPbI3 (a = 6.351 Å, Pm-3m (#221) space group) and b, PbI2 (a = b = 4.555 Å, c = 6.964 Å, P-3m1 (#164) space group) using the Diffraction Pattern Calculator (DPC) toolkit.
Extended Data Fig. 7 1D GI-WAXD profiles for the out-of-plane (qz-cut; along qxy = 0) and in-plane (qxy-cut; along qz = 0).
Crystallographic information was empirically derived from the diffraction patterns. The crystal structure of this interlayer can be assumed to be tetragonal with a = b = 5.56 Å, c = 5.29 Å. If the (001) crystal plane is oriented parallel to the substrate, the observed characteristic diffraction peaks belong to (11l) and (22l) families.
Extended Data Fig. 9 Steady-state PLs of perovskites with and without the SnO2 or TiO2 electrode on the glass substrate.
Extended Data Fig. 10 Time-resolved photoluminescence (TRPL) spectra after excitation at 520 nm (P-C-520M) with repetition rate of 200 kHz and a fluence of 34 nJ cm-2 per pulse for perovskite films on various ETLs coated on FTO substrates and perovskite without ETL on glass.
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Min, H., Lee, D.Y., Kim, J. et al. Perovskite solar cells with atomically coherent interlayers on SnO2 electrodes. Nature 598, 444–450 (2021). https://doi.org/10.1038/s41586-021-03964-8
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