Molecule‐Induced p‐Doping in Perovskite Nanocrystals Enables Efficient Color‐Saturated Red Light‐Emitting Diodes

Abstract

light with the emission wavelength of 620-640 nm is an essential part for highdefinition display; however, compared with the green-counterpart, the electroluminescence (EL) performance of the colorsaturated red and blue perovskite emitters is much poorer. Ever since the first red-PeLED with an EL peak at 630 nm was demonstrated by Friend and coworkers, [1] efforts have been paid to improve the emitter photoluminescence quantum yield (PL QY) toward high-performing devices. Tan and coworkers applied a trimethylaluminum vapor-based crosslinking method to increase the PL QY of CsPb(Br/I) 3 nanocrystals (NCs) and gave rise to an EQE of 1.4%. [28] Brighter emitters leading to more efficient LEDs have been also observed in perovskite NCs of other colors and components, and strategies including doping, [29][30][31][32][33][34] surface capping, [35][36][37][38][39][40][41] core-shell structures, [42,43] and anion-exchange [25,[44][45][46][47] have been employed. For lead-halide perovskites, most charge recombination centers are localized on the crystal surfaces, and lead atoms who may cause strong exciton quenching are facile to form. [35,[38][39][40] Thus, the PL QY of red CsPb(Br/I) 3 NCs can increase through reducing the number of surface lead atoms. Aside from the excellent optical properties, the electric conductivity of perovskite NCs is another crucial factor for the performance of perovskite electroluminescent devices. Metal doping has been considered as a promising avenue to control over the electronic and optical performance of perovskite NCs. However, the limited improvement of metal doped CsPb(Br/I) 3 PeLEDs indicates that new methods are necessary. [32] Furthermore, doping perovskite with transition metal ions (Cu 2+ , Ni 2+ , Zn 2+ ) broadened the emission bands, and incorporation of Mn 2+ or lanthanide ions introduced new emission centers in perovskite NCs, leading to poor color purity of PeLEDs. [31,33,34] Here, benzyl iodide (BI) was chosen to passivate the CsPb(Br/I) 3 NC surface where the iodide can bond to the surface Pb atoms leading to reduced non-recombination centers. Interestingly, we found that the electrons tend to transfer from CsPb(Br/I) 3 NC to the surface electron acceptor-aromatic rings, leading to p-doping of the CsPb(Br/I) 3 NCs, thus allowing us to control over the energy levels and electrical conductivity. With the help of BI, the NC PL QY is greatly increased Color-saturated red light-emitting diodes (LEDs) with emission wavelengths at around 620-640 nm are an essential part of high-definition displays. Metal halide perovskites with very narrow emission linewidth are promising emitters, and rapid progress has been made in perovskite-based LEDs (PeLEDs); however, the efficiency of the current color-pure red PeLEDs-still far lags behind those of other-colored ones. Here, a simple but efficient strategy is reported to gradually down-shift the Fermi level of perovskite nanocrystals (NCs) by controlling the interaction between NCs and their surface molecular electron acceptor-benzyl iodide ...

Phenylalkylammonium passivation enables perovskite light emitting diodes with record high-radiance operational lifetime: the chain length matters

“…As shown in the XPS spectra (Fig. 1c, d ), the binding energies corresponding to the I 3 d and Pb 4 d core levels of the passivated samples all slightly shift to higher values compared to the control sample, an indication of enhanced binding of the iodide and lead ions on the perovskite surface 29 . We also note that the shifts are more pronounced in the n = 3 and n = 4 samples.…”

Smoothing the energy transfer pathway in quasi-2D perovskite films using methanesulfonate leads to highly efficient light-emitting devices

“…9 ). The device current has a linear proportionality to the drive voltage up to the trap-filled limit ( V TFL ) 54 – 56 . It can be seen that the MeS-treated film presented a lower V TFL (1.08 V) compared to those of the control film (1.45 V), demonstrating that the trap density in the perovskite film was reduced.…”

The Impact of Precursor Ratio on the Synthetic Production, Surface Chemistry, and Photovoltaic Performance of CsPbI3 Perovskite Quantum Dots

“…[ 1–5 ] CsPbX 3 QDs exhibit excellent optical properties such as high photoluminescence quantum yields (PLQYs), narrow full width at half‐maximum (FWHM), and tunable bandgaps, which is comparable or even superior to state‐of‐the‐art CdSe QDs with sophisticated shelling or surface passivation, showing huge potential for lighting/display applications. [ 1,2,5–11 ] Recently, it was demonstrated that CsPbI 3 QDs can keep a stable black phase at room temperature, [ 12 ] whereas bulk CsPbI 3 will convert to a nonperovskite yellow phase ( δ ‐phase) with unfavorable optoelectronic properties at the temperature below 320 °C. In addition to the extraordinary phase stability, CsPbI 3 QDs also possess superior thermal stability over the widely studied organic–inorganic hybrid perovskites.…”