Highly efficient PeLEDs using gold nanoparticles modified PEDOT:PSS as the hole injection layer

Abstract

Organic-inorganic hybrid perovskite light-emitting diodes (PeLEDs) have attracted increasing attentions recently due to their great potential in flat panel display and lightening as well as other advantages such as low cost, ease of fabrication, high color purity, and tunable emission from the visible to infrared wavelengths. Improving the electroluminescent efficiency and the device stability of PeLEDs became hot spots in recent studies. To achieve highly efficient PeLEDs, two critical criteria must be satisfied: pinhole-free perovskite film to suppress leakage currents and optimized device structures with minimum injection barriers that guarantee balanced charge injection into perovskites. Over the last decades, metallic nanostructures have been focused on improving the efficiency of organic optoelectronic devices, which is mainly based on the optical and electrical effects of metal nanoparticles (NPs), including localized surface plasmon resonance (LSPR)-enhanced fluorescence, electrical properties, interface effect, light scattering, and so on. However, there is few research dedicated to the metal plasmonic enhanced electroluminescence of perovskite. Driven by this motivation, metal NPs may provide many advantages in improving the performance of PeLEDs through optimizing the device structure. In this work, gold nanoparticles (Au NPs) aqueous solution (with Au NPs diameter of ~20 nm) was first synthesized by ″Frens″ method. And then, the Au NPs modified poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), which was obtained by mixing Au NPs aqueous solution with PEDOT:PSS with a desired volume ratio of 0.2:1, was introduced into CH3NH3PbBr3-based PeLEDs as the hole injection layer. It should be noted that the ~20 nm Au NPs was fully covered by ~45 nm PEDOT:PSS layer in order to avoid direct contact with the active layer of CH3NH3PbBr3, which is critical to prevent excitions quenching by a nonradiative energy transfer process at the surfaces of the metal NPs. Results show that, the photoluminescence (PL) and electroluminescence (EL) of CH3NH3PbBr3 film are both enhanced by ~2.41 fold and ~1.48 fold by the Au NPs, respectively. For the Au NPs modified PeLEDs with structure of ITO/Au NPs: PEDOT:PSS/PVK:CH3NH3PbBr3:TPBi/TPBi/Cs2CO3/Al, the turn-on voltage was ~3.0 V, the maximum luminance was ~16050 cd/m2, and the maximum current efficiency was ~7.02 cd/A, compared to the performance of the reference PeLEDs without Au NPs modification which exhibited the turn-on voltage of ~3.2 V, the maximum luminance of ~7156 cd/m2, and the maximum current efficiency of ~4.74 cd/A. By studying the underlying mechanisms, we found that the absorption spectra of Au NPs and PL spectra of CH3NH3PbBr3 film overlapped to each other very well, indicating that the LSPR effect of Au NPs could accelerate radiative decay rate of CH3NH3PbBr3 excitions accumulated at PEDOT:PSS/CH3NH3PbBr3 interface, which is helpful in making full use of CH3NH3PbBr3 excitions by avoiding them being quenched by interfacial excess charge carriers or anode. Our studies have provided an alternative way to further improve the EL efficiency of PeLEDs through interface modification with Au NPs, which is of great importance in both fundamental study of LSPR effect of Au NPs, and their potential applications in PeLEDs.