Hole Transport Bilayer Structure for Quasi‐2D Perovskite Based Blue Light‐Emitting Diodes with High Brightness and Good Spectral Stability

Abstract

Substantial achievements have been made in green and red perovskite light emitting diodes (PeLEDs) recently. However, blue PeLEDs still lag behind with much lower performances. One of the main reasons is the mass undesirable nonradiative recombination at interfaces and within the perovskite films. In this work, an efficient hole transport bi-layer structure composed of PSSNa and NiO x is demonstrated to simultaneously inhibit the nonradiative decays between NiO x and perovskite films by reducing NiO x surface defects and improving quasi-2D perovskite thin film quality by minimizing its pin-holes and reducing the film roughness. The results show that the dipole feature of PSSNa improves the hole transportation and thus PeLED performances. Moreover, by introducing KBr into the perovskite, its film quality improves and trap states reduce. Eventually, the blue PeLEDs is achieved with a very low turn-on voltage of 3.31 V accompanied with an external quantum efficiency of 1.45% and a remarkable luminance of 4359 cd m -2 . With further optimization of the perovskite precursor concentration, the highest luminance reaches 5737 cd m -2 , which represents the brightest blue PeLEDs reported to date as far as it is known. Furthermore, the devices also show better spectral stability and operation lifetime as compared to other blue PeLEDs.

High‐Performance Blue Perovskite Light‐Emitting Diodes Enabled by Efficient Energy Transfer between Coupled Quasi‐2D Perovskite Layers

“…Perovskite Emission Layer Preparation: CsPbBr 3 powder was first synthesized according to the previous method. [15] The precursor of PEA x PA 2−x (CsPbBr 3 ) n−1 PbBr 4 perovskite was prepared by dissolving 0.15 m CsPbBr 3 powder, 0.15 m PABr, and 0.015 m PEA 2 PbBr 4 into DMSO. Then the pristine PEA x PA 2−x (CsPbBr 3 ) n−1 PbBr 4 perovskite films were obtained by spin-coating the precursor at 3000 rpm for 60 s in which 300 µL of toluene was quickly dripped on the substrate at 28 s after the spin-procedure starting, followed by annealing at 75 °C for 10 min.…”

“…[ 8–10 ] These achievements firmly prompt the potential applications of PeLEDs in display and illumination fields. However, compared with the efficient PeLEDs, there is only moderate performance reported for blue PeLEDs, [ 11–18 ] which undoubtedly restrict PeLED applications in full‐color displays and white‐light illumination. Thus, the breakthroughs of the device performance are urgently required for blue PeLEDs.…”

Interfacial Potassium‐Guided Grain Growth for Efficient Deep‐Blue Perovskite Light‐Emitting Diodes

“…[ 10,37 ] To passivate the defects and confine the quasi‐2D structures in deep‐blue perovskite films, the additives of potassium bromide (KBr), formamidine bromide (FABr), and 4‐Fluorophenylethylammonium bromide (p‐F‐PEABr) with small amount were also added in the precursor solutions (see the details in Section 4). [ 13,30,38 ] As intuitively shown in Figure S1, Supporting Information, both the absorption edges and photoluminescence (PL) spectra of the mixed‐halide (Cs/FA/p‐F‐PEA)Pb(Cl/Br) 3 perovskite films exhibit an obvious hypsochromic shift from green (509 nm) to deep‐blue (467 nm) with respect to the increase in the Cl concentration by increasing the amount of CsCl and PbCl 2 . Finally, the deep‐blue perovskite films emitting at 467 nm were obtained when the molar ratio of CsBr:CsCl:PbBr 2 :PbCl 2 was selected as 3:3:2:2.…”

Understanding the Synergistic Effect of Device Architecture Design toward Efficient Perovskite Light‐Emitting Diodes Using Interfacial Layer Engineering

“…Solution processed conducting polymer HIL/MHP interface is especially important in conventional structure PeLED where ETL is mostly formed with vacuum deposition. [ 51–54 ] In case of PEDOT:PSS, acidic PEDOT etches ITO substrate and metallic indium ion can be released an consequently migrated metallic indium species in the MHP layer induce non‐radiative recombination and strongly reduce the luminescence. [ 51 ] Inorganic NiO x , another conventional HIL, is also reported to quench the PL, which is attributed to existence of non‐radiative recombination in their defect sites or charge transfer process at the HIL/MHP interface.…”