Band Edge Control of Quasi‐2D Metal Halide Perovskites for Blue Light‐Emitting Diodes with Enhanced Performance

Abstract

Perovskite light-emitting diodes (PeLEDs) have received great attention for their potential as next-generation display technology. While remarkable progress has been achieved in green, red, and near-infrared PeLEDs with external quantum efficiencies (EQEs) exceeding 20%, obtaining high performance blue PeLEDs remains a challenge. Poor charge balance due to large charge injection barriers in blue PeLEDs has been identified as one of the major roadblocks to achieve high efficiency. Here band edge control of perovskite emitting layers for blue PeLEDs with enhanced charge balance and device performance is reported. By using organic spacer cations with different dipole moments, that is, phenethyl ammonium (PEA), methoxy phenethyl ammonium (MePEA), and 4-fluoro phenethyl ammonium (4FPEA), the band edges of quasi-2D perovskites are tuned without affecting their band gaps. Detailed characterization and computational studies have confirmed the effect of dipole moment modification to be mostly electrostatic, resulting in changes in the ionization energies of ≈0.45 eV for MePEA and ≈ −0.65 eV for 4FPEA based thin films relative to PEA-based thin films. With improved charge balance, blue PeLEDs based on MePEA quasi-2D perovskites show twofold increase of the EQE as compared to the control PEA based devices.

High-Throughput Evaluation of Emission and Structure in Reduced-Dimensional Perovskites

“…We speculate that this shifts the band gap by effectively deprotonating the PEA and increasing the electronegativity of the amino group . Our observation is corroborated by a recent study in which 4-MeO-PEABr was used to tune the band edge and improve the charge balance and device performance of CsPbBr 3 -based LEDs . This result was also observed in the 4-MeO-PEAI perovskite that demonstrated a consistently narrower fwhm (∼66 nm) and stronger emission during HTC than its nonfunctionalized parent ligand PEAI and OH-PEAI as seen in Figure a.…”

Engineering Highly Fluorescent and Colloidally Stable Blue-Emitting CsPbBr3 Nanoplatelets Using Polysalt/PbBr2 Ligands

“…11 Although great success has been achieved in fabricating greenand red-emitting perovskite NC-based LEDs, the efficiency of devices emitting in the blue region of the optical spectrum still needs improvements. 2,4 Similar to many other luminescent compounds, developing blue-emitting perovskite materials with high PLQYs and long-term photophysical stability remains difficult to achieve, compared to their green-and red-emitting counterparts. For the latter, samples with nearunity PLQY have been prepared and tested, via either optimization of the growth reaction or postsynthetic passivation of the NC surfaces.…”

Unravelling Alkali‐Metal‐Assisted Domain Distribution of Quasi‐2D Perovskites for Cascade Energy Transfer toward Efficient Blue Light‐Emitting Diodes

“…[23][24][25][26] Moreover, treating the substrates (usually, hole-transport layers) with suitable alkali-metal ions is found to be promising to reduce the interfacial defects for optimized growth of perovskite films that lead to the enhanced device performance. [19][20][21][22][23][24][25][26][27][28] Tang and co-workers introduced potassium ions (K + ) in poly (3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and the resulting K + -modified substrate rendered perovskite films with high surface coverage and controlled crystal orientation, leading to an EQE of 4.14% with a maximum luminance of 451 cd m −2 for blue emission at 469 nm. [19] To manipulate the domain distribution of Q-2D perovskites to realize efficient energy funneling towards improved light-emission, reports show that introduction of alkali-metal halides can be a potential alternative to long-chain organic spacers.…”