Organometal Halide Perovskite Quantum Dot Light‐Emitting Diodes

Abstract

4797wileyonlinelibrary.com photoluminescence quantum yields (PLQY). Organometal halide perovskite quantum dots (OHP-QDs) have recently emerged as bright emitters with narrow-band colors and high PLQY (up to ≈90%). [11][12][13][14] Furthermore, tuning the size or halide compositions of OHP-QDs has enabled fi ne adjustment of their emitting colors across the entire visible spectrum. [ 12,13 ] These attractive characteristics highlight the enormous potential of OHP-QDs as light-emitting materials in electroluminescence (EL) devices.However, OHP-QDs-based LEDs (OQ-LEDs) have been rarely reported, primarily due to the diffi culties in the fabrication of dense fi lms of OHP-QDs for effi cient emitting layers. OHP-QDs are usually prepared by solvent exchange or hot injection methods, but the concentration of the resultant OHP-QDs suspension is low (≈0.5 mg mL −1 ). [ 12,13 ] The subsequent enrichment of the OHP-QDs suspension is diffi cult due to easy aggregation and/or potential damage of OHP-QDs during the concentration process via evaporation. [ 15 ] As a result, it is hard to form a continuous fi lm of OHP-QDs from dilute suspensions using a common spin-coating or printing method. The lack of effi cient fabrications of dense and uniform fi lms of OHP-QDs has greatly hampered their use in high-performance EL devices.In this work, we report one-step fabrication of high-quality uniform fi lms of OHP-QDs by using a simple dip-coating method. By varying the halide composition (X = Br, Cl, and I) or tuning the size of OHP-QDs, we can readily produce uniform fi lms of OHP-QDs emitting with tunable colors from blue to green and red. Based on the OHP-QDs fi lms, we fabricated multicolor higheffi ciency OQ-LEDs with sharp emissions (FWHM smaller than 30 nm). The packaged OQ-LEDs showed robust stability in air of ≈50% humidity for at least 7 d. The remarkable performance characteristics of OQ-LEDs demonstrate the high potential of OHP-QDs as effi cient and color-tunable light emitters for lowcost display, lighting, and optical communication applications.Organometal halide perovskites quantum dots (OHP-QDs) with bright, colortunable, and narrow-band photoluminescence have signifi cant advantages in display, lighting, and laser applications. Due to sparse concentrations and diffi culties in the enrichment of OHP-QDs, production of large-area uniform fi lms of OHP-QDs is a challenging task, which largely impedes their use in electroluminescence devices. Here, a simple dip-coating method has been reported to effectively fabricate large-area uniform fi lms of OHP-QDs. Using this technique, multicolor OHP-QDs light-emitting diodes (OQ-LEDs) emitting in blue, blue-green, green, orange, and red color have been successfully produced by simply tuning the halide composition or size of QDs. The blue, green, and red OQ-LEDs exhibited, respectively, a maximum luminance of 2673, 2398, and 986 cd m −2 at a current effi ciency of 4.01, 3.72, and 1.52 cd A −1 , and an external quantum effi ciency of 1.38%, 1.06%, and 0.53%, which are much bette...

Research Update: Challenges for high-efficiency hybrid lead-halide perovskite LEDs and the path towards electrically pumped lasing

“…With these crystals, full-colour PeLEDs can be fabricated, and their photograph and emission spectra are shown in Figure 3(c). 30,39,40 After the report of Protesescu et al, Zhang et al reported the synthesis of organic-inorganic hybrid perovskite quantum dots with PLQEs up to 70% and demonstrated the application of them as an alternative phosphor for white-light LEDs. 41 Afterwards various synthesis routes have been reported.…”

“…The highest electroluminescence quantum efficiencies in PeLEDs produced by the precursor method are 8.8% (near infrared, ∼760 nm) 21 and 8.53% (green, ∼520 nm), 20 respectively. The best EQE of PeLEDs prepared by nanocrystal dispersions is 1.38% (blue), 39 3.8% (green), 66 and 5.7% (red).…”

“…39 In an ideal case, PeLED nanocrystal dispersions should be fully purified from impurities and the spin-coated film should have smooth topography.…”

“…80 To form a uniform perovskite nanocrystal film, Kim et al used a centrifuging method for purification 72 and Deng et al used a dip coating method. 39 As another significant problem, these nanocrystals are very dispersible in most common solvents, limiting the solution-processing of the top layer. In order to fix the nanocrystal film in place, Palazon et al found that X-ray radiation is able to crosslink the nanocrystal film and maintain photoluminescence at the same time, 81 while Li et al found that a vapour-based cross-linking is able to fix the nanocrystals in place without damaging the transport and emission property of the nanocrystal film.…”

“…73 Up to the current date, the best operational time of perovskite light-emitting diodes after packaging is ∼10 days/240 h. 39 This value has to be improved by ∼40 times in the future to meet commercial requirements. The earliest report by Tan et al attributes the device degradation and efficiency roll-off to a heating effect at high current density.…”