The poor interface characteristics between inorganic perovskite and the electron transport layer limit the improvement of the photovoltaic performance of inorganic perovskite solar cells (IPSCs). In this paper, the buried interface was treated with ethylenediaminetetraacetic acid (EDTA), and four carboxyl groups of EDTA reacted with the hydroxyl groups of SnO₂ to improve the interface characteristics, enhance the crystallization quality of the inorganic perovskite film, reduce the defect state density and suppress non-radiative recombination. Finally, the n-i-p type device with the composition of CsPbI_2.25Br_0.75 prepared in air achieved a power conversion efficiency (PCE) of 18.84% and excellent stability.

The In-doped Tin Oxide (ITO) glass substrate was ultrasonically cleaned in glass cleaner, deionized water and isopropyl alcohol solution for 20 min, respectively. Before the use, the FTO substrate was treated with ultraviolet ozone for 20 min. Then, 12% SnO₂ nanosolution was diluted for three times with water and spin-coated on the surface of ozone-treated ITO glass at 3000 r/min for 30 s, followed by annealing in air at 150 ℃ for 30 min. After cooling to room temperature, 0.1 mg/mL EDTA (H₂O) was spin-coated on the surface of SnO₂ and annealed at 100 ℃ for 10 min. The preparation of perovskite precursor solution and thin film was consistent with the that from previously reported literature^[30], except that the preparation environment of the perovskite film was changed in air with a humidity of < 25%. 40 μL of Spiro-OMeTAD was spin-coated on the surface of perovskite film at 3000 r/min for 30 s as a hole transport layer. Finally, 80 nm of Au was evaporated on the surface of the hole transport layer by evaporation equipment as a metal electrode.

The pinholes on the surface of the perovskite in the Target group are significantly reduced, corresponding to a lower defect state density and a superior photovoltaic performance. The PL intensity of the Target group films is significantly greater than that of the Control group, indicating that non-radiative recombination is suppressed after EDTA treatment. After EDTA treatment, the average carrier lifetime increases from 75.10 ns to 113.31 ns. The optimum PCE is increased from 16.68% of the control device to 18.84%. The current density is verified by the external quantum efficiency test of the solar cell. The integral current density increases from 18.42 mA/cm² to 18.78 mA/cm² due to the improvement of the interface contact characteristics between SnO₂ and perovskite by EDTA. The steady-state output power curve of the best PCE device of the target device is negligible within 280 s. Two types of devices are placed in an environment at 25 ℃ and a humidity of 20%-30%. After 250 h, the control device retains 73.39% of its initial PCE, while the Target device maintains 81.41%. The improvement in stability is attributed to the EDTA enhancement of the interface contact between SnO₂ and the inorganic perovskite, suppressing non-radiative recombination at the interface and reducing the defect state density.

The EDTA was used to modify the buried interface. The four carboxyl groups of EDTA reacted with the hydroxyl groups of the SnO₂ layer, improving the interface contact characteristics between SnO₂ and perovskite and facilitating the efficient extraction of electrons. Non-radiative recombination at the interface was suppressed and the defect state density was reduced. Ultimately, a n-i-p type device with a composition of CsPbI_2.25Br_0.75 prepared in air achieved a PCE of 18.84%. This could provide a scientific approach for advancing the practical application of IPSCs.