In recent years, metal halide perovskites have shown promising potential in a series of optoelectronic applications such as solar cells, light-emitting diodes (LEDs), photodetectors and lasers. The booming research on metal halide perovskites can be attributed to their superior optoelectronic properties such as high absorption coefficient, long charge carrier diffusion length, high photoluminescence quantum yield (PLQY) and high defect tolerance. In particular, owing to the nature of their facile color tunability, solution processability and sharp emission, metal halide perovskites have been successfully applied in LEDs, extending the family of emitters.
However, compared with the efficient near-infrared, red and green perovskite LEDs with external quantum efficiency (EQE) exceeding 20%, blue perovskite LEDs currently still suffer from inferior performance. To be specific, state-of-the-art blue perovskite LEDs exhibit EQE lower than 3% and half-lifetime around several minutes or even seconds. Improving performance remains a great challenge and limits the development of possible applications such as full-color displays and white-light illumination based on perovskite LEDs. Therefore, a breakthrough in thin-film perovskite LEDs with blue emission is an urgent target in this field.
Our research group (Hin-Lap Yip, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology) has been dedicated to investigating the use of an integrated approach combining materials, interface, and device engineering to improve both polymer and perovskite photovoltaic and light emitting devices. In our recent work, we demonstrated that the efficiency of blue perovskite LEDs can be improved by combining three key strategies: composition engineering, dimensional engineering and modulation of recombination zone position. First, through composition and dimensional engineering, we prepare quasi-two-dimensional perovskite thin films with improved blue emission, taking advantages of reduced trap density and enhanced photoluminescence properties. Second, we observed that the perovskite crystals are non-uniformly distributed in the PEDOT:PSS/perovskite hybrid film along the vertical direction. Therefore, by systematically modulating the position of the recombination zone through controlling the charge injection property of the devices, we enable the majority of carriers recombining at the perovskite crystal-rich region, and thus demonstrate the most efficient blue perovskite light-emitting diode to date with emission peak at 480 nm, record luminance of 3780 cd m-2 and record external quantum efficiency of 5.7%. The demonstration of efficient blue perovskite LEDs paves the way for the realization of full-color displays and white-light illumination with perovskite LEDs.
The related paper has been published in Nature Communications. Please see details:
Zhenchao Li, Ziming Chen, Yongchao Yang, Qifan Xue, Hin-Lap Yip* and Yong Cao. Modulation of recombination zone position for quasi-two-dimensional blue perovskite light-emitting diodes with efficiency exceeding 5%. Nat. Commun. DOI: 10.1038/s41467-019-09011-5