Zwitterions Narrow Distribution of Perovskite Quantum Wells for Blue Light‐Emitting Diodes with Efficiency Exceeding 15%

Abstract

Since the first room temperature lead halide perovskite light-emitting diode (PeLED) reported in 2014, [5] green, red, and near-infrared PeLEDs have been developed rapidly, with external quantum efficiency (EQE) all over 20%. [6][7][8][9][10][11][12] However, the EQE of blue PeLEDs is still lagging behind, [13][14][15][16] which undoubtedly restricts their applications in full-color displays and white-light illuminations. [2,[17][18][19] Recently, quasi-2D perovskites have been considered as emerging candidates for efficient blue emission, with high exciton binding energy and efficient radiative recombination, thanks to the quantum confinement and dielectric confinement effects. [20][21][22][23] In quasi-2D perovskites, large organic ligands such as butylammonium (BA + ) and phenylethylammonium (PEA + ) can divide the perovskite lattice into a finite number of inorganic monolayers (n) and form quantum wells. While quasi-2D perovskites offer a feasible approach for high-efficiency blue PeLEDs, the elaborate control over the distribution of n domains presents a rising challenge. [24] Solution processed quasi-2D perovskites often contain a mixture of n phases with various bandgaps. [24,25] While quasi-two-dimensional (quasi-2D) perovskites have emerged as promising semiconductors for light-emitting diodes (LEDs), the broad-width distribution of quantum wells hinders their efficient energy transfer and electroluminescence performance in blue emission. In particular, the underlying mechanism is closely related to the crystallization kinetics and has yet to be understood. Here for the first time, the influence of bifunctional zwitterions with different coordination affinity on the crystallization kinetics of quasi-2D perovskites is systematically investigated. The zwitterions can coordinate with Pb 2+ and also act as co-spacer organic species in quasi-2D perovskites, which collectively inhibit the aggregation of colloidal precursors and shorten the distance of quantum wells. Consequently, restricted nucleation of high-n phases and promoted growth of low-n phases are achieved with moderately coordinated zwitterions, leading to the final film with a more concentrated n distribution and improved energy transfer efficiency. It thus enables high-efficiency blue LEDs with a recorded external quantum efficiency of 15.6% at 490 nm, and the operation stability has also been prolonged to 55.3 min. These results provide useful directions for tuning the crystallization kinetics of quasi-2D perovskites, which is expected to lead to high-performance perovskite LEDs.

Tuning the energy transfer in Ruddlesden–Popper perovskites phases through isopropylammonium addition – towards efficient blue emitters

“…But for blue-emitting PeLEDs, the progress in efficiency has been lagging behind, although many efforts have been dedicated to improving these devices. 12–25 Recently, a record EQE of 17.9% has been reported by ligand manipulation in on-substrate synthesis of quantum dots. 26…”

“…But for blue-emitting PeLEDs, the progress in efficiency has been lagging behind, although many efforts have been dedicated to improving these devices. [12][13][14][15][16][17][18][19][20][21][22][23][24][25] Recently, a record EQE of 17.9% has been reported by ligand manipulation in on-substrate synthesis of quantum dots. 26 At least three major approaches have been used to fabricate efficient blue-emissive MHP layers with high values of photoluminescence quantum yields (PLQYs), which acts as a primary indicator for a promising emissive layers in emitting devices technology.…”

“…26 At least three major approaches have been used to fabricate efficient blue-emissive MHP layers with high values of photoluminescence quantum yields (PLQYs), which acts as a primary indicator for a promising emissive layers in emitting devices technology. 27 These three approaches rely on the use of active layers of very different nature, namely: (i) 3D MHPs, 15,25,28 (ii) quasi-2D perovskites, 17,21,22,29,30 and (iii) nanocrystals based on 3D MHPs. 16,23,31 The first approach has the advantage of the good charge transport properties of 3D perovskites, which contribute to improve the EQE.…”

“…37 This relation between optical and structural-properties makes quasi-2D perovskites a promising candidate for light emission applications. Both Ruddlesden-Popper (RP) 17,21,29,30,38 as well as Dion-Jacobson (DJ) phases, 22,39,40 the two most common quasi-2D perovskites structures, already achieved remarkable performance in blue-emitting PeLEDs with record EQE above 15%. 21,22 RP phases are currently the most investigated, thanks to the more favourable formation energy of middle-n phases (such as n = 3) and the less efficient energy transfer from 2D to 3D phases, both key factors to obtain blue-emitting PeLEDs.…”

“…Both Ruddlesden-Popper (RP) 17,21,29,30,38 as well as Dion-Jacobson (DJ) phases, 22,39,40 the two most common quasi-2D perovskites structures, already achieved remarkable performance in blue-emitting PeLEDs with record EQE above 15%. 21,22 RP phases are currently the most investigated, thanks to the more favourable formation energy of middle-n phases (such as n = 3) and the less efficient energy transfer from 2D to 3D phases, both key factors to obtain blue-emitting PeLEDs. 41,42 The interesting properties of quasi-2D perovskites, and in particular of the RP phases, come with several challenges, as to control the phase distribution and their orientation to favour charge transport.…”