Spectrally Stable Blue Light-Emitting Diodes Based on All-Inorganic Halide Perovskite Films.

Substantial progress has been made in perovskite light-emitting diodes (PeLEDs), but the fabrication of high-performance blue PeLEDs still remains a challenge due to its low efficiency, spectral instability and short operational lifetime. How to produce an efficient and stable blue PeLED is the key to realizing the application of PeLEDs in full-color displays. We herein report a blue PeLED usint the ligand-assisted reprecipitation method, in which phenylethylammonium bromide (PEABr) was used as ligands, and chloroform was used as anti-solvent to prepare blue perovskite nanocrystal films. By increasing the PEABr content from 40% to 100% (The ratio of x% PEABr refers to the molar ratio between PEABr and PbBr2), the film quality is highly improved, and the emission exhibits a blue shift. Introducing a poly(9-vinylcarbazole) (PVK) hole transport layer into the device, the PVK layer can not only achieve efficient hole injection, but can also isolate the PEDOT: PSS layer to inhibit the non-radiative recombination of metal halide luminescence layer, reduce surface ion defects and successfully inhibit halide atom migration. Finally, the PeLED presents a stable electroluminescence under different driving voltages without any red shift.

Improving the voltage tolerance of perovskite light-emitting diodes via a charge-generation layer.

A high electrical field is necessary to achieve a high brightness for halide perovskite light-emitting diodes (PeLEDs). Charge accumulation in the perovskite film becomes more serious under a high electrical field owing to the imbalanced charge injection in PeLEDs. Concomitantly, the perovskite film will suffer from a higher electrical field increased by the accumulated-charge-induced local electrical field, dramatically accelerating the ion migration and degradation of PeLEDs. Here we construct a voltage-dependent hole injection structure consisting of a ZnO/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) bilayer, which can properly adjust the hole injection according to the driving electrical field, matching with the injected electrons. As a result, the ZnO/PEDOT:PSS-containing PeLED can be operated under higher driving voltage with a higher peak brightness of 18920 cd/m2, which is 84% higher than the reference device based on a PEDOT:PSS single layer. Moreover, the ZnO/PEDOT:PSS-containing PeLED delivers a much higher power efficiency than the reference device under high driving voltages.

Achieving high-performance in situ fabricated FAPbBr3 and electroluminescence.

Currently, metal halide perovskite films still encounter the issues of inferior film quality and interfacial electrical properties when they were constructed electroluminescence devices. Herein, efficient and pinhole-free perovskite emissive film was obtained on the poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) layer modified by an ultrathin LiF layer. Owing to the synergetic effect of the LiF interlayer, including better regulation of the perovskite film and a more balanced charge injection capability, an efficient green light-emitting diode based on the perovskite film was achieved with a maximum current efficiency of 25.6 cd/A, which is 58% higher than that of the control device with a plasma-treated PEDOT:PSS layer. Our results not only provide a facile strategy for acquiring efficient perovskite films but also circumvent the expensive and time-consuming plasma treatment process commonly used to improve the wetting properties of the underlying films.