Sky-blue perovskite light-emitting diodes based on quasi-two-dimensional layered perovskites

A mixed organic（4-phenylbutylamine, 4-PBA） and inorganic（cesium, Cs） cations are used to deposit quasi-two-dimensional layered perovskites. This layered perovskites exhibit good film coverage as twodimensional perovskites and high emission performance close to three-dimensional organic–inorganic hybrid perovskites. Light-emitting diodes（LEDs） are fabricated by using solution process based on the quasi-two-dimensional layered perovskites. The perovskite LEDs exhibit a sky-blue emission with electroluminescence peak at 491 nm and a low turn on voltage at 2.9 V. The maximum external quantum efficiency reaches 0.015% at brightness of 186 cd/m^2.

Temperature-dependent self-trapped exciton emission in Cu(I) doped zinc-based metal halides from well-resolved excited state structures

Zero-dimensional metal halides are of unique structures and tunable photoluminescence properties,showing great potential applications such as light-emitting diodes(LEDs)and sensing.Herein,we successfully synthesized Cu^(+)doped(MA)_(2)ZnCl_(4)metal halides by a slow evaporation solvent method.The introduction of Cu^(+)results in sky-blue self-trapped exciton emission in(MA)_(2)ZnCl_(4) at 486 nm at room temperature,and a photoluminescence quantum yield is as high as 54.9%.Interestingly,at low temperatures,Cu^(+)-doped(MA)_(2)ZnCl_(4) exhibits two emission peaks located at 482 and 605 nm,respectively.This temperaturedependent dual emission indicates two excited state structures that exist on the triplet excited-state potential energy surface.In addition,the temperature sensor we fitted has good performance(Sr=1.65%·K^(−1)),which is the first attempt in Cu^(+) doped Znbased metal halides.Our work enriches the family of sky-blue metal halides and provides a promising strategy for building skyblue LEDs.

High-efficiency thermally activated delayed fluorescence materials via a shamrock-shaped design strategy to enable OLEDs with external quantum efficiency over 38%

To achieve highly-efficient organic light-emitting diodes(OLEDs),great efforts have been devoted into constructing thermally activated delayed fluorescence(TADF)with high horizontal dipole ratios(Θ//).Here,we proposed a design strategy by integrating a rigid electron-accepting oxygen-bridged boron core with triple electron-donating groups,which exhibited a“shamrock-shape”,namely BO-3DMAC and BO-3DPAC.Benefiting from the rigid and large-planar skeletons brought by shamrock-shaped design,BO-3DMAC and BO-3DPAC exhibit highΘ//of 84%/70%and 93%/94%in neat/doped films,respectively,and finally furnish excellent external quantum efficiencies(EQEs)of up to 28.3%and 38.7%in 20 wt%doped OLEDs with sky-blue emission,as well as adequate EQEs of up to 21.0%and 16.7%in nondoped OLEDs.This work unveils a promising strategy to establish high-Θ//TADF emitters by constructing large-planar molecular structures using shamrock-shaped design.

Performance improvement of DBP-based solar cells by introducing a luminescent sensitizer bis[(4,6-difluorophenyl)-pyridinato-N,C^(2')]c(picolinate)iridium(III)(Flrpic)

In this work,a sky-blue luminescent down-shifting(LDS)layer bis[(4,6-difluorophenyl)-pyridinato-N,C^(2')]c(picolinate)iridium(II)(FIrpic)was inserted between tetraphenyl dibenzoperiflanthene(DBP)and Mo0_(3)as UV-screen and sensitizer for smallmolecule DBP/C_(60)based planar heterojunction(PHJ)solar cells.With 8-nm Flrpic theshort circuit current(J_(sc))and power conversion efficiency(PCE)of the device areenhanced by 28%and 15%,respectively,probably originating from the re-absorption ofthe photons emitted from Flrpic.The V_(oc)linearly increases over 1-nm Flrpic,ascribed tothe deeper HOMO level of Flrpic than DBP,while the fill factor continuously declines from 3-to 10-nm Flrpic.The EQE spectra prove that the J_(sc)is mainly contributed by thephotocurrent generated in DBP and C_(60)layers.When the FIrpic thickness is 8 nm,the filmsurface is very uniform with the smallest water contact angle.The impedance spectro-scopy demonstrates that the device resistance gradually increases from 4.1×10^(4)Ω(without Flrpic)to 4.6×10^(4)Ω(with 10-nm Flrpic)with the FIrpic thickness rise,simultaneously the device transits from the insulating state into the conductive statefaster for the thin Flrpic layer than the thick layer.

Carbazole ring: A delicate rack for constructing thermally activated delayed fluorescent compounds with through-space charge transfer

Three carbazole derivatives, Ac PTC, Px PTC and Pt PTC, consisting of two 9,9-dimethyl-9,10-dihydroacridine,phenoxazine or phenothiazine donor groups and one diphenyltriazine acceptor group fixed at 1,8,9-positions of a single carbazole ring via phenylene, are designed and synthesized. X-ray diffraction analysis of Ac PTC reveals that there exist multiple π-π interactions between the donor and acceptor groups to form a sandwich-like structural unit with edge-to-face interaction model. The compounds thus show obvious thermally activated delayed fluorescence with through-space charge transfer character and possess considerable photoluminescence quantum yields of up to 73% in doped films with sky-blue to yellow emissions. The solution-processed electroluminescent devices achieve the highest maximum external quantum efficiencies of 10.0%, 11% and 5.6% for Ac PTC, Px PTC and Pt PTC, respectively, with small efficiency roll-offs.