Jakub Jagielski

Aggregation-induced through-space charge transfer can be used to tune single-fluorophore emission in simple polymer systems.

Colloidal nanocrystals (NCs) of lead halide perovskites have generated considerable interest in the fabrication of optoelectronic devices, such as light emitting-diodes (LEDs), because of their tunable optical bandgap, narrow spectral width, and high defect tolerance. However, the inhomogeneous halide distribution within individual NCs remains a critical challenge in order to obtain color-stable electroluminescence in mixed-halide systems. Here, we demonstrate a new post-synthetic approach, ligand-assisted solid phase synthesis (LASPS), for the preparation of electroluminescent colloidal NCs of methylammonium (MA) lead halide perovskites, at room temperature. The slow reaction kinetics preserves the morphology, size, and shape in the resulting NCs whose emission covers the entire visible spectral region with photoluminescence (PL) quantum yields (QYs) of up to >90% and colloidal stability up to several months. The LEDs fabricated using the prepared mixed-halide NCs display narrowband electroluminescence (EL) ranging from 476 to 720 nm. The optimized red LEDs exhibit an external quantum efficiency, η_ext, of up to 2.65%, with the CIE 1931 color coordinates of (0.705, 0.290), nearly identical to those of the red primary in the recommendation (rec.) 2020 standard (0.708, 0.292).

Efficient OLED devices have been fabricated using organometallic complexes of platinum group metals. Still, the high material cost and low stability represent central challenges for their application in commercial display technologies. Based on its innate stability, gold(III) complexes are emerging as promising candidates for high‐performance OLEDs. Here, a series of alkynyl‐, N‐heterocyclic carbene (NHC)‐ and aryl‐gold(III) complexes stabilized by a κ³‐(N^C^C) template have been prepared and their photophysical properties have been characterized in detail. These compounds exhibit good photoluminescence quantum efficiency (η_PL) of up to 33 %. The PL emission can be tuned from sky‐blue to yellowish green colors by variations on both the ancillary ligands as well as on the pincer template. Further, solution‐processable OLED devices based on some of these complexes display remarkable emissive properties (η_CE 46.6 cd.A⁻¹ and η_ext 14.0 %), thus showcasing the potential of these motifs for the low‐cost fabrication of display and illumination technologies.

We report efficient perovskite nanocrystal LEDs based on a new electron transport material, BBIA , possessing high electron mobility of 4.17 × 10 ⁻⁴ cm ² V ⁻¹ s ⁻¹ . BBIA -based devices exhibit a nearly two-fold enhancement than TPBi counterpart.

Flexible perovskite light-emitting diodes (LEDs) have attracted increasing interest to realize ultrathin, light weight, highly conformable and nonfragile vivid displays. Solution-processed lead halide perovskite offers numerous distinctive characteristics such as pure emission color, tunable bandgaps, and low fabrication cost. In this work, green perovskite LEDs (PeLEDs) are fabricated on 50 μm thick polyimide substrates. Using colloidal 2D formamidinium lead bromide perovskite emitter, the PeLEDs show a high current efficiency (ηCE) of 5.3 cd A-1 with a peak emission at 529 ± 1 nm and a narrow width of 22.8 nm. The resultant green emission shows color saturation > 95%, in the Rec. 2020 standard gamut area. To demonstrate mechanical flexibility, the device functionality is tested by dynamic bending experiments down to 10 mm for up to 5000 cycles, resulting in device lifetime over 36 h in a glove box and a drop of ηCE and external quantum efficiency (ηext) as low as 15% and 18%, respectively. For the selective activation of multiple PeLEDs, 7 × 7 passive arrays on rigid and flexible substrates are demonstrated. Moreover, preliminary results of active matrices show the compatibility of PeLEDs with oxide-based Thin-Film Transistors (TFTs) for display applications.

Hybrid lead halide perovskites, described by a formula ABX₃, recently emerged as a new class of semiconducting materials for various optoelectronic devices. Especially, colloidal perovskites exhibit numerous favorable properties, such as high photoluminescence quantum yield (PLQY), tunable bandgap, defect tolerance, high charge carrier mobility, large exciton binding energy (E_B ), outstanding color purity (FWHM < 25 nm) and low cost of production, for high efficiency solution-processed light-emitting diodes (LEDs).^[1] Analogously to conventional, inorganic quantum dots (QDs), quantum confinement effects could be observed upon forming colloidal perovskite nanoplatelets (NPLs) with thicknesses below ~10 unit cells (n < 10). Taking MAPbBr₃ for example, we demonstrate a facile synthetic route to obtain monodisperse colloidal solutions of layered perovskites with precise control from n = 1 to n = 7-10 layers.^[2] These layer controlled perovskite NPLs not only offer a color-tunable emission, but also enhance the E_B . The resultant high E_B is crucial to enable efficient radiative recombination of excitons. Most interestingly, our layer controlled NPLs also showed record high solid-state PLQYs (50-85%) for blue and green emission. With this approach we were able to demonstrate efficient pure-blue electroluminescence at room temperature using colloidal 2D perovskites. On the other hand, in order to meet the requirement for ultrapure green emission which targets the Rec.2020 recommendation, FAPbBr₃ perovskite NPLs were utilized. Through dielectric quantum well (DQW) engineering high exciton binding energy of 162 mV was achieved which further resulted in superior PLQY value of 92%. The optimized active layer LEDs exhibited a maximum current efficiency of 13 cd/A but most importantly with its CIE 1931 color coordinates (0.168, 0.773) it represents the “greenest” LED ever reported.^[3] Motivated by harsh market requirements, we were able to further improve the performance of ultrapure green device over 2-fold through compositional engineering. Using colloidal, ultrapure green emitting perovskite nanocrystals such result has never been reached so far. This opens an avenue towards low-cost and high-throughput production of solution-processed LEDs. [1] J. Jagielski, S. Kumar, W.-Y. Yu, C.-J. Shih, Journal of Materials Chemistry C 2017, 5, 5610. [2] S. Kumar, J. Jagielski, S. Yakunin, P. Rice, Y.-C. Chiu, M. Wang, G. Nedelcu, Y. Kim, S. Lin, E. J. G. Santos, M. V. Kovalenko, C.-J. Shih, ACS Nano 2016, 10, 9720. [3] S. Kumar, J. Jagielski, N. Kallikounis, Y.-H. Kim, C. Wolf, F. Jenny, T. Tian, C. J. Hofer, Y.-C. Chiu, W. J. Stark, T.-W. Lee, C.-J. Shih, Nano Letters 2017, 17, 5277.

The outstanding excitonic properties, including photoluminescence quantum yield (η _PL), of individual, quantum-confined semiconductor nanoparticles are often significantly quenched upon aggregation, representing the main obstacle towards scalable photonic devices. Here we report aggregation-induced emission (AIE) phenomena in the lamellar solids containing layer-controlled colloidal quantum wells (CQWs) of hybrid organic-inorganic lead bromide perovskites, resulting in anomalously high solid-state of up to 94%. Upon forming the QW solids, we observe an inverse correlation between exciton lifetime and , clearly distinct from that in typical quantum dot solid systems. Our multiscale theoretical analysis reveals that in a lamellar solid, the collective motion of the surface organic cations are more restricted to orient along the [100] direction, thereby inducing a more direct bandgap that facilitates radiative recombination. Using the QW solids, we demonstrate ultra-pure green emission by completely downconverting a blue GaN light emitting diode (LED) at room temperature, with a luminous efficacy higher than 90 lm/W at 5,000 cd/m², which has never been reached in any nanomaterial assemblies by far [1]. [1] Jagielski et al., Science Advances, accepted manuscript (2017)

We demonstrate ultra-pure green and efficient light emitting diodes (LEDs) by employing the colloidal perovskite nanoplatelets (NPLs). Through the dielectric quantum wells engineering and aggregation induced emission, the perovskite NPLs exhibit an anomalously high photoluminescence quantum efficiency (η_PL) of 94% and a higher exciton binding energy (E_B) in the thin solid films. The optimized devices show a high current efficiency of >20 cd A⁻¹ and a maximum external quantum efficiency over 5%. The color gamut covers >97% of the Rec. 2020 gamut area in the CIE 1931 color space, demonstrating the “greenest” LEDs ever reported. We also present large-area (30 mm²) and flexible LEDs based on perovskite NPLs.

The outstanding excitonic properties, including photoluminescence quantum yield (η_PL), of individual, quantum-confined semiconductor nanoparticles are often significantly quenched upon aggregation, representing the main obstacle toward scalable photonic devices. We report aggregation-induced emission phenomena in lamellar solids containing layer-controlled colloidal quantum wells (QWs) of hybrid organic-inorganic lead bromide perovskites, resulting in anomalously high solid-state η_PL of up to 94%. Upon forming the QW solids, we observe an inverse correlation between exciton lifetime and η_PL, distinct from that in typical quantum dot solid systems. Our multiscale theoretical analysis reveals that, in a lamellar solid, the collective motion of the surface organic cations is more restricted to orient along the [100] direction, thereby inducing a more direct bandgap that facilitates radiative recombination. Using the QW solids, we demonstrate ultrapure green emission by completely downconverting a blue gallium nitride light-emitting diode at room temperature, with a luminous efficacy higher than 90 lumen W⁻¹ at 5000 cd m⁻², which has never been reached in any nanomaterial assemblies by far.

Pure green light-emitting diodes (LEDs) are essential for realizing an ultrawide color gamut in next-generation displays, as is defined by the recommendation (Rec.) 2020 standard. However, because the human eye is more sensitive to the green spectral region, it is not yet possible to achieve an ultrapure green electroluminescence (EL) with a sufficiently narrow bandwidth that covers >95% of the Rec. 2020 standard in the CIE 1931 color space. Here, we demonstrate efficient, ultrapure green EL based on the colloidal two-dimensional (2D) formamidinium lead bromide (FAPbBr₃) hybrid perovskites. Through the dielectric quantum well (DQW) engineering, the quantum-confined 2D FAPbBr₃ perovskites exhibit a high exciton binding energy of 162 meV, resulting in a high photoluminescence quantum yield (PLQY) of ∼92% in the spin-coated films. Our optimized LED devices show a maximum current efficiency (η_CE) of 13.02 cd A^–1 and the CIE 1931 color coordinates of (0.168, 0.773). The color gamut covers 97% and 99% of the Rec. 2020 standard in the CIE 1931 and the CIE 1976 color space, respectively, representing the “greenest” LEDs ever reported. Moreover, the device shows only a ∼10% roll-off in η_CE (11.3 cd A^–1) at 1000 cd m^–2. We further demonstrate large-area (3 cm²) and ultraflexible (bending radius of 2 mm) LEDs based on 2D perovskites.