Multifunctional p‐Type Carbon Quantum Dots: a Novel Hole Injection Layer for High‐Performance Perovskite Light‐Emitting Diodes with Significantly Enhanced Stability

Abstract

rich chemical and structural diversity of these solution-processed MHPs enables a series of fascinating luminescent materials for perovskite light-emitting diodes (PeLEDs). [2] Benefit from the perovskite film morphology controlling, composition adjusting, dimensionality tuning, optical coupling, and interface engineering, the external quantum efficiencies (EQEs) of PeLEDs have rapidly increased from below 1% to over 20% in 5 years. [3] With the increasing quantum yield of perovskite emission layer, the reported EQE values of PeLEDs are even comparable to the best performing quantum dot light-emitting diodes. [4] However, the excitons quenching at the interfacial between emission layer and charge transport layers still limit the further increase of luminescence efficiency. Suppressing the energy loss at the interfaces becomes the key to the realization of the near-unity radiative recombination for PeLED devices.In a conventional PeLED device structure, the conducting polymer poly(3,4ethylenedioxythiophene):poly styrene sulfonate (PEDOT:PSS) is the most commonly used a hole injection layer (HIL). However, the exciton quenching effect at interface between emission and PEDOT:PSS layers seriously restricts the device performance including the EQE and long-term device stability. The modification of PEDOT:PSS has been extensively studied to alleviate For metal halide perovskite (MHP)-based light-emitting diodes (PeLEDs), effective radiative recombination of the injected holes and electrons within the MHP layer and minimized injection energy barriers at the interfaces between MHP emission layer and charge injection layers are prerequisites for high-performance and stable PeLEDs. Herein, for the first time, novel p-type carbon quantum dots (CQDs) are introduced as a hole injection layer in PeLEDs to replace acidic poly(3,4-ethylenedioxythiophene):poly styrene sulfonate (PEDOT:PSS) layer. The CQDs demonstrate high hole transport mobility and desirable hole injection energy level. Moreover, the carboxyl, amine, and hydroxyl groups on CQDs not only offer a hydrophilic surface for high-quality perovskite layer growth, but also passivate the perovskite surface defects to suppress the interfacial exciton quenching. Based on the multifunctional p-type CQDs, high-performance green CsPbBr 3 PeLEDs with a low turn-on voltage of only 2.8 V, maximum luminance of 25 770 cd m −2 , and maximum external quantum efficiency (EQE) of 13.8% are achieved. The PeLEDs also show good operational stability and long-term environmental stability. The first application of CQDs as a hole injection layer in PeLEDs breaks through the traditional cognition of carbon materials and opens up new pathways for the developments of carbon nanomaterials in optoelectronic devices.

Controlling Spatial Crystallization Uniformity and Phase Orientation of Quasi‐2D Perovskite‐Based Light‐Emitting Diodes Using Lewis Bases

“…The fitting parameters are summarized in Table S1 (Supporting Information). The long decay component is ascribed to charge recombination, while the fast decay is caused in part by charge transfer to PEDOT:PSS . The average PL lifetime and the lifetime of the long decay component were found to increase when the films were spin‐coated with a mixture of DMF and a Lewis base additive.…”

Highly Stable All‐Inorganic Perovskite Quantum Dots Using a ZnX2‐Trioctylphosphine‐Oxide: Application for High‐Performance Full‐Color Light‐Emitting Diode

“…There are a few materials reported so far for perovskite LEDs that meet these requirements. [ 40–43 ] In this study, we used the new cross‐linkable HTL of VB‐FNPD, which has transparency, the proper HOMO and LUMO levels of 5.4 and 2.4 eV, relatively high hole‐carrier mobility of 1.00 × 10 −4 cm 2 V −1 s −1[ 44 ] compared to commercial HTL of polyvinylcarbazole (PVK, hole mobility: 2.50 × 10–6 cm 2 V −1 s −1[ 45 ] ), cross‐linking properties for multilayer preparation, and the proper surface energy based on the contact angle data. First, for the hole‐injection property of VB‐FNPD, the hole‐only device (HOD) including PVK or VB‐FNPD was fabricated in all three colors.…”

Insulator as Efficient Hole Injection Layer in Perovskite Light‐Emitting Device via MIS Contact

“…Lead halide perovskites have shown great potentials as light‐emitting materials in light‐emitting diodes (LEDs) due to their outstanding optical and electrical properties. [ 1–11 ] Perovskites are solution‐processable materials with sharp emission peak (full width at half maximum ≈20 nm) and their emission spectra can be easily tuned by adjusting the ratio of halide components. [ 12–16 ] The first room temperature operating perovskite light‐emitting devices (PeLEDs) were reported in 2014 [ 17 ] and the external quantum efficiency (EQE) has reached over 20% in just a few years.…”