Conjugated Polyelectrolytes as Multifunctional Passivating and Hole‐Transporting Layers for Efficient Perovskite Light‐Emitting Diodes

Abstract

Recently, metal halide perovskites (MHPs) have attracted increasing attention as promising emitting materials for use in light-emitting diodes (LEDs), because of their high color purities and facile color tunabilities. [1][2][3][4][5][6][7] However, the low exciton binding energy of MHPs results in the thermal dissociation of the excitons at room temperature, [8][9][10] leading to poor geminate radiative recombination. The generated free charges are trapped in defect states rather than undergoing radiative decay, resulting in trap-mediated nonradiative charge recombination. To overcome the poor radiative recombination yield, several strategies, including reduction in perovskite grain size [7,11,12] and use of quasi-2D perovskites, [5,6,13,14] have been employed to promote bimolecular radiative recombination. Defect passivation in MHPs is a potential solution for enhancing the luminescent properties by employing various passivating materials containing amine (NH 2 ), [4,15,16] hydroxyl (OH), [17,18] phosphine oxide (PO), [6,19,20] carbonyl (CO), carboxyl (COOH), [21,22] and ammonium bromide Metal halide perovskites (MHPs) have attracted significant attention as light-emitting materials owing to their high color purities and tunabilities.A key issue in perovskite light-emitting diodes (PeLEDs) is the fabrication of an optimal charge transport layer (CTL), which has desirable energy levels for efficient charge injection while blocking opposite charges and enabling perovskite layer growth with reduced interfacial defects. Herein, two poly(fluorene-phenylene)-based anionic conjugated polyelectrolytes (CPEs) with different counterions (K + and tetramethylammonium (TMA + )) are presented as multifunctional passivating and hole-transporting layers (HTLs). The crystal growth of MHPs grown on different HTLs is investigated through X-ray photoelectron spectroscopy, X-ray diffraction, and density functional theory calculation. The CPE bearing the TMA + counterions remarkably improves the growth of perovskites with suppressed interfacial defects, leading to significantly enhanced emission properties and device performance. The luminescent properties are further enhanced via aging and electrical stress application with effective rearrangement of the counterions on the interfacial defects in the perovskites. Finally, efficient formamidinium lead tribromide-based quasi-2D PeLEDs with an external quantum efficiency of 10.2% are fabricated. Using CPEs with varying counterions as a CTL can serve as an effective method for controlling the interfacial defects and improving perovskite-based optoelectronic device properties. Perovskite Light-Emitting DiodesThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Optimizing Interfacial Energetics for Conjugated Polyelectrolyte Electron Injection Layers in High Efficiency and Fast Responding Polymer Light Emitting Diodes

“…Recently, CPEs have found use as interlayer materials in organic optoelectronic devices. 4 − 7 In particular, thin (5–20 nm) CPE electron injection layers (EILs) have been found to greatly enhance electron injection from high workfunction electrodes into polymer light-emitting diodes (PLEDs) and improve device efficiency. 1 , 3 , 8 − 13 This allows CPEs to replace traditional low workfunction metals that are both less stable and less environmentally friendly.…”

A-Site Cation Engineering for Efficient Blue-Emissive Perovskite Light-Emitting Diodes

“…A 0.45 µm hydrophilic filter were used for the perovskite precursor solutions filtration. Filtered perovskite precursor solutions were spin-coated at 3000 rpm for 50 s. The antisolvent, chlorobenzene (300 µL), was dropped after 30 s, as described elsewhere [26]. TPBi, lithium fluoride (LiF), and aluminum (Al) electrodes were evaporated using a thermal evaporator.…”

Improvement of photoluminescence intensity and film morphology of perovskite by Ionic liquids additive

“…The increase of defects will further make it easier for excitons to be trapped by defects and then form non-radiative recombination. Some of the most noteworthy approaches include doping the perovskite materials with alkalications, which has been demonstrated to control bulk defects and eliminate hysteresis [12][13][14] . That can greatly improve the quality of perovskite morphology and reduce the density of trap states.…”