Gold nanoparticals modified indium tin oxide anode for high performance red perovskite light emitting diodes

Abstract

Gold nanoparticles (Au NPs) play an important role in improving the external quantum efficiency of perovskite light emitting diodes (PeLED). To avoid direct contact between the Au NPs and the light emitting layer, the Au NPs@SiO₂ structure and blending the Au NPs into the hole transport layer (HTL) or electron transport layer (ETL) have been proposed previously. However, the Au NPs@SiO₂ is difficult to obtain and affects the charge transport. When the Au NPs is blended in poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT: PSS), the density of Au NPs is not easily controlled and the PEDOT:PSS is not an ideal HTL for PeLED. Therefore, the electrostatic adsorption is used in this work to uniformly disperse the ~20 nm-size Au NPs on the top of the ITO anode, and the Poly(9-vinylcarbazole) (PVK) is spin-coated as the HTL to achieve the high performance red PeLED based on the (NMA)₂Cs_<i>n</i>–1Pb_<i>n</i>I_3<i>n</i>+1. After the Au NPs modification, the maximum luminous brightness rises from ~5.2 to ~83.2 cd/m². Meanwhile, the maximum external quantum efficiency rises from ~0.255% to ~6.98%. Mechanism studies show that microcavity can be formed between the Au NPs-modified ITO anode and the Al cathode, and the transmitted light and the reflected light interfere with each other to improve the output couple efficiency of the PeLED. The photoluminescence (PL) spectrum and angle dependent PL intensity of the Au NPs-modified PeLED prove that the fluorescence enhancement of the (NMA)₂Cs_<i>n</i>–1Pb_<i>n</i>I_3<i>n</i>+1 perovskite is attributed mainly to the microcavity effect. Furthermore, the effects of Au NPs density on the performance of the PeLED are investigated, which reveals that the device with ~15 min adsorption is optimal. Finally, we rule out the contributions of Au NPs to the morphology, crystallization, electrical properties and localized surface plasmon resonance (LSPR) effects of (NMA)₂Cs_<i>n</i>–1Pb_<i>n</i>I_3<i>n</i>+1 perovskite films. In this work, the Au NPs are successfully applied to red PeLED for the first time, providing a feasible way of developing the low-cost and high-efficiency PeLED.