Effects of in-situ annealing on the electroluminescence performance of the Sn-based perovskite light-emitting diodes prepared by thermal evaporation

Abstract The Sn-based perovskite light-emitting diodes (PeLED) with the structure of (ITO)/MoO3/4,4′-cyclohexylidenebis[N,N-bis(p-tolyl)aniline](TAPC)/4,4′,4′-Tris(carbazol-9-yl)-triphenylamine (TCTA)/perovskite/1,3,5-Tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB)/lithium fluoride(LiF)/Al were fabricated by thermal evaporation and in-situ annealing. The perovskite emitting layers were annealed at the various temperature of 50, 75 and 85 °C during the dual sources thermal evaporation of CsBr and SnBr2 instead of routine post-synthetic annealing for the formation of crystalline CsSnBr3 film. The effects of annealing temperature on the morphology, structure and photophysical properties of the CsSnBr3 perovskite films as well as the electroluminescence(EL) performance of the PeLED were investigated. Little temperature dependence of perovskite emitting layers' morphology was found while obviously intensified absorbance, crystallinity and steady-state photoluminesce(PL) as well as apparently increased PL decay lifetime and slight red-shifted PL spectra of the CsSnBr3 perovskite films upon increasing in-situ annealing temperature were demonstrated. The similar temperature dependent behavior of steady-state PL intensity, transient PL decay life time and photoluminescence quantum yield(PLQY) of all the CsSnBr3 films verified that the hybrid effect of suppressed deep acceptor states and enhanced emitting from shallow trap states would be responsible for the PL behavior of in-situ annealed CsSnBr3 films. In-situ annealing was also capable of extending carriers lifetime and reducing trap density, and leading to the occurrence of the suppressed “self-doping” of Sn4+ and reduction of acceptor states. Meanwhile, the improved crystal quality of the CsSnBr3 nanocrystals should be closely related to the enhanced charge carriers dynamics and improved PL performance. The PeLED with 85 °C in-situ annealed CsSnBr3 emitting layer demonstrated optimal EL performance with the current efficiency(CE) of 0.34 cd/A and external quantum efficiency(EQE) of 0.16%, which was consistent with the annealing temperature dependence of PL behavior of the CsSnBr3 perovskite emitting layer and could be attributed to its superior PL performance, low trap density and high crystallinity.