Xinyu Shen

Abstract:

LED light bulbs that simulate solar spectrum were fabricated using CdSe core-shell quantum dots in combination with GaN blue-light chips. They exhibited excellent optical properties such as white CIE coordinates of (0.33, 0.33), high color rendering index (CRI) of 98 and correlated color temperature (CCT) of 5352 K. Moreover, a circuit system was used to control the LEDs so that the lighting spectrum changes with the time in a day to simulate the actual solar spectrum. The results show that the sun-like spectrum smart bulbs not only have good optical properties and high electrical stability, but also can automatically adjust their spectrum according to the time, making the lighting natural. This work makes sun-like lighting conditions for some special environments to promote the application of smart bulbs in smart lighting.

Abstract:

2D transition metal carbides, nitrides, and carbonitrides called MXenes show outstanding performance in many applications due to their superior physical and chemical properties. Herein, a ZnO-MXene mixture with different contents of Ti₃ C₂ is applied as electron transport layers (ETLs) and the influence of the Ti₃ C₂ MXene in all-inorganic metal halide perovskite nanocrystal light-emitting diodes (perovskite NC LEDs) is explored. The addition of Ti₃ C₂ makes more balanced charge carrier transport in LEDs by changing the energy level structure and electron mobility of ETL. Moreover, lower surface roughness is obtained for the ETL, thus guaranteeing uniform distribution of the perovskite NCs layer and further reducing leakage current. As a result, a 17.4% external quantum efficiency (EQE) with low efficiency roll-off is achieved with 10% Ti₃ C₂ , which is a 22.5% improvement compared to LEDs without Ti₃ C₂ .

Abstract:

AbstractCoherent light sources in silicon photonics are the long‐sought Holy Grail because silicon‐based materials have indirect bandgap. Traditional strategies for realizing such sources, e.g., heterogeneous photonic integration, strain engineering, and nonlinear process, are technologically demanding. Here, a hybrid lasing device composed of perovskite nanocrystals and silicon nitride nanobeam cavity is demonstrated. SiN photonic crystal naonobeam cavities are fabricated on a solid substrate with significantly improved thermal and mechanical stabilities compared to conventional suspended ones. In addition, adding a poly (methyl methacrylate) (PMMA)‐encapsulation layer on top of the SiN can significantly boost the Q‐factor of the cavity mode. By dispersing perovskite nanocrystals as emitters in the PMMA layer, high‐performance coherent emissions are obtained in terms of lasing threshold, linewidth, and mode volumes. The work offers a compelling way of creating solution‐processed active integrated photonic devices based on the mature platform of silicon photonics for applications in optical information science and photonic quantum technology.

Abstract:

AbstractThe external quantum efficiencies (EQEs) of perovskite quantum dot light‐emitting diodes (QD‐LEDs) are close to the out‐coupling efficiency limitation. However, these high‐performance QD‐LEDs still suffer from a serious issue of efficiency roll‐off at high current density. More injected carriers produce photons less efficiently, strongly suggesting the variation of ratio between radiative and non‐radiative recombination. An approach is proposed to balance the carrier distribution and achieve high EQE at high current density. The average interdot distance between QDs is reduced and this facilitates carrier transport in QD films and thus electrons and holes have a balanced distribution in QD layers. Such encouraging results augment the proportion of radiative recombination, make devices with peak EQE of 12.7%, and present a great device performance at high current density with an EQE roll‐off of 11% at 500 mA cm−2 (the lowest roll‐off known so far) where the EQE is still over 11%.

Abstract:

Perovskite nanocrystal light-emitting devices (PNC LEDs) exhibit great potential in display and lighting applications. Balanced hole and electron injection in the light-emitting layer is undoubtedly an effective way to improve LED performance. Here, bismuth (Bi) was introduced into PNC LEDs to form a silver-bismuth (Ag-Bi) bilayer anode. Ag diffused into a defective 2 nm thick Bi layer to form an alloy-like state that promoted hole injection, reduced the charge transfer resistance, and enhanced charge transfer, leading to more balanced hole-electron carriers in the emission layer through hole injection enhancement. As a result, the turn-on voltage and brightness changed from 2.41 V and 2200 cd m^-2, respectively, for CsPb_1-xZn_xI₃-based LEDs with a Ag monolayer anode to 2.2 V and 3714 cd m^-2, respectively, for devices with a Ag-Bi bilayer anode. In addition, the performance of CsPbI₃ and CsPbBrI₂ PNC-based LEDs has also been effectively improved by using a Ag-Bi bilayer anode.