Near‐Unity Quantum Yield and Superior Stable Indium‐Doped CsPbBr_xI_3−x Perovskite Quantum Dots for Pure Red Light‐Emitting Diodes

Abstract

The reported external quantum efficiencies (EQEs) of red-emitting PeLEDs based on CsPbBr x I 3−x perovskite are listed in Table S1 (Supporting Information). However, the soft basic nature of I − [1,[16][17][18][19] and the phase separation arising from halide ion migration cause low stability of CsPbBr x I 3−x PeQDs, making CsPbBr x I 3−x more difficult to apply to pure red PeLEDs. [11] Therefore, pure red PeLEDs based on CsPbBr x I 3−x perovskite with a high EQE and excellent stability remain a huge challenge. In previous research, the photoluminescence (PL) quantum yield (PLQY) and stability of PeQDs have been explored, including encapsulation by adding silicon oxide or aluminum oxide, [20,21] passivation of quantum dots (QDs) by PbSe, [22] and the use of additional ligands. [2,9,12,[23][24][25] However, the above-mentioned insulative oxide, PbSe, and ligands inevitably hinder the charge transfer of PeQDs, resulting in poor conductivity.Recently, a new strategy for metal ion doping has been proposed to improve the PLQY and stability of PeQDs, [10,[26][27][28][29][30][31][32][33][34] and solve the problem of lead toxicity. [31,35,36] For example, Yang et al. used K + ions to acquire high-color-stable red PeLEDs by the passivation effect, whereas the EQE of K + -PeLEDs was only 3.55%. [10] PeQDs modified by lanthanide (Ln 3+ ) ions were more stable than the corresponding pristine sample. [29] The PeQDdoped Sn 2+ soft ions contributed to the limited stability in applications, in which Sn 2+ ions were easily oxidized to Sn 4+ in air. [31] In addition to these metal ions, metal In 3+ ions have attracted attention in the field of solar cell applications. Liu et al. reported that an improvement in the power conversion efficiency of 13% for CsPbI 2 Br solar cells was obtained because the In 3+ ions located diagonally adjacent to Pb passivated the defects of the CsPbI 2 Br perovskite film. [36] However, to the best of our knowledge, In 3+ ions are rarely used in PeLEDs. Therefore, the synthesis of In 3+ -doped PeQDs and the passivation mechanisms of In 3+ ions are essential for studying the production of higher PLQY and more stable PeLEDs.In this study, a near-unity quantum yield (QY) and superior stable red-emitting CsPbBr x I 3−x PeQDs were obtained by adopting nontoxic and slightly smaller radii of In 3+ ions. It was found that the surface defect can be passivated by In 3+ doping, Although all-inorganic CsPbBr x I 3−x perovskite quantum dots (PeQDs) are increasingly being used as a competitive material for pure red perovskite light-emitting diodes (PeLEDs), they suffer from low luminescent ability and poor stability. In this study, an In 3+ -doped CsPbBr x I 3−x PeQD solution exhibits a near-unity photoluminescence quantum yield (PLQY) of ≈99.8% and superior stability for more than half a year in atmosphere. As far as known, this is the highest PLQY and stability achieved for mixed halide PeQDs. In 3+ ion doping not only reduces the surface vacancy defects because of the partial substitution of Pb 2+ by the smaller ...

Recent Progress in Mixed A‐Site Cation Halide Perovskite Thin‐Films and Nanocrystals for Solar Cells and Light‐Emitting Diodes

“…[6,[48][49][50][51][52][53][54][55] Over the last 7 years, research on perovskite NCs has explored their synthesis, surface chemistry, optical and electronic properties along with their applications. [6,14,50,[56][57][58] The concept of A-site cation compositional engineering has also been extended to colloidal LHP NCs to fine-tune their optical properties as well as to improve their phase stability. [47,[59][60][61] The mixed A-cation LHP NCs are of great interest for the fabrication of durable LEDs and solar cells.…”

An effective Fe(ii) doping strategy for stable and highly photoluminescent CsPbBrI2 nanocrystals

“…The lattice contraction induced by Fe 2+ doping strengthens the ligand field of the [PbX 6 ] 4À octahedra, resulting in the blue shift of the PL peak. 31 The PLQYs and time-resolved photoluminescence (TRPL) measurement were then carried out to investigate the influence of Fe 2+ doping on the relaxation process of CsPbBrI 2 NCs. The PLQY of undoped CsPbBrI 2 NCs was measured to be 69.2%, which was comparable to the results reported in the literature.…”

“…The lattice contraction induced by Fe 2+ doping strengthens the ligand field of the [PbX 6 ] 4− octahedra, resulting in the blue shift of the PL peak. 31…”

“…Over the past few years, a number of metal ion-doped PNCs have been developed and investigated. [30][31][32][33] For instance, Cu 2+ (R B = 0.73Å) doped CsPbBrI 2 NCs with a PLQY of 81.3% were obtained through a hot injection method and 69.4% of PLQY was retained after 30 days of storage under ambient conditions. 24 Gd 3+ (R B = 0.93 Å) doped CsPbBrI 2 NCs with excellent water stability were obtained through a melting quenching method and the brightness of CsPbBrI 2 remained stable after 60 days in water.…”

Metal Halide Perovskites for Red‐Emission Light‐Emitting Diodes

“…By introducing Mn 2þ , Zn 2þ , Sr 2þ , Cu 2þ , Ca 2þ , Bi 3þ , Y 3þ , In 3þ , and other metals to partially replace Pb 2þ , the metal ions with smaller radius can reduce the average radius of the B site (r B þ ). [106][107][108][109][110][111][112] Thus, it increases the tolerance factor and achieves stable CsPbI 3 perovskite materials. It is worthy to pay attention to the phase segregation when applied this method, especially the halide segregation.…”