High efficiency green perovskite light-emitting diodes based on exciton blocking layer

Abstract

In recent years, metal halide perovskite materials, owing to their excellent photoelectric properties including high photoluminescence quantum yield, high color purity, tunable band gap, etc., have been regarded as new-generation lighting sources and are widely used to fabricate perovskite light-emitting diodes (PeLEDs). Though great progresses have been made in recent years, neither the efficiency nor stability has not yet reached the requirements of commercialization. Thus, further improvement is needed. In this work, a small organic molecule material, namely 4,4'-cyclohexylidenebis[N,N-bis(p-tolyl)aniline] (TAPC) with a wide bandgap and a good hole transport ability, is used as an exciton blocking layer by utilizing the spin-coating method to improve the stability and efficiency of PeLEDs. Highly efficient and stable CsPbBr<sub>3</sub> PeLEDs are finally realized. The physical mechanism related to the improved electroluminescence performance is investigated thoroughly. Firstly, the stepped energy level alignment is formed, since the highest occupied molecular orbital energy level (HOMO) of TAPC is located between the HOMO of (3,4-ethylenedioxythiophene):poly(p-styrene sulfonate) (PEDOT: PSS) and the valence band of CsPbBr<sub>3</sub>, which is beneficial to hole injection and transport. Meanwhile, the lowest unoccupied molecular orbital level of TAPC is high enough to prevent electrons from leaking into the anode effectively and confine electrons and excitons well in the emitting layer. Secondly, the introduction of the TAPC layer can avoid the direct contact between the perovskite light emitting layer and the strong acidic layer of PEDOT:PSS, thereby eliminating the related excitons quenching, which can further increase the radiative recombination.