Enhanced Photoelectric Properties of CsPbBr₃ by SiO₂ and TiO₂ Bilayer Heterostructures

CsPbBr₃/SiO₂ heterostructures were synthesized by the hydrolysis reaction of a mixture of CsPbBr₃ nanocrystals (NCs) and (3-aminopropyl)triethoxysilane (APTS) in air. Compared with CsPbBr₃ NCs, the CsPbBr₃/SiO₂ heterostructures exhibit stronger photoluminescence (PL) intensity, longer lifetime of PL (∼40.5 ns), and higher PL-quantum yield (PLQY, ∼86%). The carrier dynamics of CsPbBr₃/SiO₂ was detected by the transient absorption (TA) spectrum. The experimental results show that SiO₂ passivates the surface traps of CsPbBr₃ NCs and enhances the PL intensity. However, photoelectrochemical impedance spectra (PEIS) demonstrate that the impedance of CsPbBr₃/SiO₂ is higher than that of CsPbBr₃ NCs, which reduces carrier transport and extraction. Because the application of CsPbBr₃/SiO₂ in optoelectronics is limited, CsPbBr₃/SiO₂/TiO₂ heterostructures were synthesized by the further reaction of tetrabutyl titanate (TBT). The TiO₂ coating can reduce the impedance of the CsPbBr₃/SiO₂. Importantly, ∼68% of the PL intensity of CsPbBr₃/SiO₂ is retained. Compared with CsPbBr₃/SiO₂ and CsPbBr₃ NCs, the CsPbBr₃/SiO₂/TiO₂ demonstrates faster carrier transport (κ_ct = 2.4 × 10⁹ s^-1) and higher photocurrent density (J = 76 nA cm^-2). In addition, CsPbBr₃/SiO₂/TiO₂ shows good stability under (ultraviolet) UV irradiation, along with water stability and thermal stability. Therefore, the double protection approach can enhance the stability of CsPbBr₃ NCs and tune the optoelectronic properties of CsPbBr₃ NCs.