Perovskite Photo-Sensors with Solution-Processed TiO₂ under Low Temperature Process and Ultra-Thin Polyethylenimine Ethoxylated as Electron Injection Layer

A perovskite photo-sensor is promising for a lightweight, thin, flexible, easy-to-coat fabrication process, and a higher incident photon-to-current conversion efficiency. We have investigated perovskite photo-sensors with a solution-processed compact TiO₂ under a low-temperature process and an ultra-thin polyethylenimine ethoxylated (PEIE) as an electron injection layer. The TiO₂ film is grown from an aqueous solution of titanium tetrachloride (TiCl₄ ) at 70^◦ C by a chemical bath deposition method. For an alternative process, the ultra-thin PEIE is spin coated on the TiO₂ film. Then, the perovskite layer is deposited on the substrate by the one-or two-step methods in the glovebox. Next, a hole transport layer of 2,2,7,7-tetrakis(N,N-di-p-methoxyphenylamine)-9, 9-spiro-bifluorene (Spiro-OMeTAD) solution is spin coated. The fabricated device structure is a photodiode structure of FTO/TiO₂ /(without or with) PEIE/(one-or two-step) perovskite layer/Spiro-OMeTAD/Au. For the sensing characteristics, a ratio of photo-to-dark-current density was 2.88 × 10⁴ for the device with PEIE layer. In addition, a power-law relationship is discussed.