Improving the efficiency of perovskite light emitting diode using polyvinylpyrrolidone as an interlayer

A few nanometer-thick polyvinylpyrrolidone (PVP) interlayer between PEDOT:PSS anode and active layer was introduced in a perovskite light-emitting diode (PeLED) in conjunction with nanocrystal pinning (NCP) process. The device with the PVP interlayer exhibited dramatic improvements in performance resulting in current efficiency of 20.89 cd A(-1), external quantum efficiency (EQE) of 5.4%, the luminance of 39,023 cd m(-2), and FWHM of 18 nm, despite the fact that some degree of intermixing of the layers was expected because identical solvent was used for all three layers (PEDOT:PSS, PVP, and perovskite). The interface between PVP and perovskite layer was investigated by using x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) sputter depth profiling with Ar gas cluster ion beam. Although obtaining a clear interface in XPS depth profile data was not possible because of partial interlayer mixing and the thinness of the PVP layer, an obvious difference across the interface was extracted in the UPS data. The observed energy level diagram was consistent with the characteristic of hole-only device (HOD) in which charge injection from PEDOT:PSS anode to the perovskite layer was suppressed due to the PVP layer.