Simultaneous Surface Modification and Defect Passivation on Tin Oxide–Perovskite Interfaces using Pseudohalide Salt of Sodium Tetrafluoroborate

Abstract

Passivating electron‐transporting layers (ETLs) with alkali salts have demonstrated a facial approach that is essential in healing defective surfaces, consequently improving the functionality and stability of perovskite‐based solar cells (PSCs). Herein, the pseudohalide salt of sodium tetrafluoroborate, whose anions have a higher electronegativity than other halide salts (i.e., iodide and chloride), with the potential to passivate the surface of tin oxide while enhancing the optoelectronic properties of a perovskite film, is presented. Meanwhile, the density functional theory calculations show that BF4−/F− ions exhibit a robust ionic interaction with an uncoordinated Sn4+ site. In contrast, the Na ion is bound to an oxygen atom of the OH− group, which helps reduce surface defect states and improves charge transfer properties. Thus, the best PSC exhibits a current density of 23.51 mA cm−2, an open‐circuit voltage of 1.10 V, and an excellent fill factor of 80.48, providing an efficiency of 20.82%, which exceeds that of a control device (18.38%). Importantly, the retention of the power conversion efficiency on NaBF4‐based PSCs without encapsulation is 18.44% after 1000 h of aging under ambient conditions, whereas the retention of a control device is only 16.08%.

Reconstruction of the Indium Tin Oxide Surface Enhances the Adsorption of High‐Density Self‐Assembled Monolayer for Perovskite/Silicon Tandem Solar Cells

“…[32] This can also be confirmed by the presence of F 1s peak (Figure S2d, Supporting Information), which suggest that the singly-bonded OH T s are well passivated by the F T s during the PA-SAMs adsorption. It was previously reported that the surface fluorination is robust enough to compete with and prevent the surface interaction with the hydroxyl groups from moisture at terminal-oxygen sites, that is, the displacement of F T s by OH T s. [33] These F T s on the ITO surface can not only prevent the direct contact of ITO with perovskite active layer, but also effectively passivate perovskite buried defects by forming strong hydrogen and ionic bonds with perovskite lattices. [30] To gain a more comprehensive understanding of the difference in the ITO surface termination induced by the surface reconstruction, complementary Fourier transform infrared spectroscopy (FTIR) measurements were performed at each step of the surface modification.…”

Dual Interfacial Tin-Oxide Layer with Chloride Salt for High-Performance and Durable Perovskite Solar Cells

“…This combined effect of optimizing the perovskite grain size serves to elevate the overall efficiency, performance, and reliability of perovskite solar cells. Second, the interaction between Pb 2+ and Cl – mitigates leaked current originating from excessive Pb 2+ at crystal grain boundaries, thereby increasing shunt resistance . Third, the dopant of Cl – creates a stronger electric field within the SnO 2 ETL, thereby contributing to lower series resistance at the interface between ETL and the perovskite film …”

“…Second, the interaction between Pb 2+ and Cl − mitigates leaked current originating from excessive Pb 2+ at crystal grain boundaries, thereby increasing shunt resistance. 37 Third, the dopant of Cl − creates a stronger electric field within the SnO 2 ETL, thereby contributing to lower series resistance at the interface between ETL and the perovskite film. 38 The incident photon-to-current conversion efficiency (IPCE) spectra and integrated J sc curves are presented in Figure 4b.…”

Superhalogen modulation: an effective approach for minimizing light-induced halide segregation in MAPb(I0.7Br0.3)3

“…The addition of superhalogen (highly electronegative inorganic compounds with greater electron affinities than monoatomic halogens) anionic species, 28,29 ), is proven to be an effective approach [30][31][32][33][34][35] for passivating the vacancies/interstitials of halide anions and/or organic cations with the increased activation energy of ion migration. These superhalogen anions have similar ionic radii to I − ions (the ionic radii of BF 4 − and I − are 218 and 220 pm, respectively), which are expected to substitute I vacancies/interstitials.…”