Fig. 2: Energy level diagrams and optical properties for the PVK/C60 interface with and without TPPC treatment.

a Energy level diagram of the PVK/C60 interface with TPPC treatment. Evac represents the vacuum level energy, Ec represents the conduction band energy, Ev represents the valence band energy. Ef1 and Ef2 represent the fermi level energy of bulk perovskite and the TPPC-treated perovskite surface, respectively. b KPFM images. c Potential distribution profiles along the blue dashed lines shown in (b). d PL spectra. e Measured TRPL spectra under the 450 nm laser illumination (fluence: 12.74 nJ cm−2, repetition rate: 1 MHz). f PLQYs for PVK, PVK/C60, PVK + TPPC and PVK + TPPC/C60 layers under the Xenon lamp illumination (wavelength: 450 nm, power density: 2.27 mW cm−2). The error bars show the standard deviations of 5 layers.