Attaining pure single-photon emission is key for many quantum technologies, from optical quantum computing to quantum key distribution and quantum imaging. The past 20 years have seen the development of several solid-state quantum emitters, but most of them require highly sophisticated techniques (e.g., ultrahigh vacuum growth methods and cryostats for low-temperature operation). The system complexity may be significantly reduced by employing quantum emitters capable of working at room temperature. Here, we present a systematic study across ∼170 photostable single CsPbX3 (X: Br and I) colloidal quantum dots (QDs) of different sizes and compositions, unveiling that increasing quantum confinement is an effective strategy for maximizing single-photon purity due to the suppressed biexciton quantum yield. Leveraging the latter, we achieve 98% single-photon purity (g(2)(0) as low as 2%) from a cavity-free, nonresonantly excited single 6.6 nm CsPbI3 QDs, showcasing the great potential of CsPbX3 QDs as room-temperature highly pure single-photon sources for quantum technologies.

https://pubs.acs.org/doi/pdf/10.1021/acs.nanolett.2c00756

Room-Temperature, Highly Pure Single-Photon Sources from All-Inorganic Lead Halide Perovskite Quantum Dots

Mesoporous Silica-Coated CsPbX3 Nanocrystals with High Stability and Ion-Exchange Resistance for Bright White-Emitting Displays

All-inorganic perovskite nanocrystals (PNCs) have been anticipated to be used in efficient and stable perovskite optoelectronic devices because of their suitable bandgap, broad absorption spectrum, and high color purity. However, long-term stability remains a major obstacle for the commercial application of PNCs. In particular, for red-emissive perovskites, the reaction to the environment is more sensitive than that for the green counterpart, which makes a phase transformation easily occur at room temperature. On the basis of CsPbI3 PNCs, we analyze the main instability factors of red-emissive PNCs (620–720 nm), including their structures, optoelectronic properties, and instability mechanism. We then summarize some strategies to improve the stability and performance of the perovskites and light-emitting diodes (LEDs). Furthermore, we discuss the challenge of scaling up the production of PNCs. Finally, we propose possible perspectives for the development of perovskite materials. 

Recent Progress in the Stability of Red-Emissive Perovskite Nanocrystals for Light-Emitting Diodes

Despite their low band gap, the utility of CsPbI3 nanocrystals (NCs) in solar photovoltaic and optoelectronic applications is rather limited because of their phase instability and photoluminescence (PL) intermittency. Herein we show that phase-pure, monodispersed, stable and highly luminescent CsPbI3 NCs can be obtained by tweaking the conventional hot-injection method employing NH4I as an additional precursor. Single-particle studies show a significant suppression of PL blinking. Among all NCs studied, 60% exhibit only high-intensity ON states with a narrow distribution of intensity. The remaining 40% of NCs exhibit a much wider distribution of PL intensity with a significant contribution of low-intensity OFF states. Excellent characteristics of these CsPbI3 NCs are shown to be the result of NH4+ replacing some surface Cs+ of an iodide-rich surface of the NCs. These phase-stable and highly luminescent CsPbI3 NCs with significantly suppressed PL blinking can be useful single-photon emitters and promising materials for optoelectronic and solar photovoltaic applications.

Phase-Stable and Highly Luminescent CsPbI3 Perovskite Nanocrystals with Suppressed Photoluminescence Blinking.

Mn2+-Doped CsPbI3 Nanocrystals for Perovskite Light-Emitting Diodes with High Luminance and Improved Device Stability

Black phase CsPbI3 perovskites have emerged as one of the most promising materials for use in optoelectronic devices due to their remarkable properties. However, black phase CsPbI3 usually possesses poor stability and involves a phase change process, resulting in an undesired orthorhombic (δ) yellow phase. Here, the enhanced stability of CsPbI3 nanocrystals is achieved by incorporating the Cu2+ ion into the CsPbI3 lattice under mild conditions. In particular, the Cu2+-doped CsPbI3 film can maintain red luminescence for 35 days in air while the undoped ones transformed into the nonluminescent yellow phase in several days. Furthermore, first-principles calculations verified that the enhanced stability is ascribed to the increased formation energy due to the successful doping of Cu2+ in CsPbI3. Benefiting from such an effective doping strategy, the as-prepared Cu2+-doped CsPbI3 as an emitting layer shows much better performance compared with that of the undoped counterpart. The turn-on voltage of the Cu2+-doped quantum-dot light-emitting diode (QLED) (1.6 V) is significantly reduced compared with that of the pristine QLED (3.8 V). In addition, the luminance of the Cu2+-doped QLED can reach 1270 cd/m2, which is more than twice that of the pristine CsPbI3 QLED (542 cd/m2). The device performance is believed to be further improved by optimizing the purification process and device structure, shedding light on future applications.

Cu2+-Doped CsPbI3 Nanocrystals with Enhanced Stability for Light-Emitting Diodes.

A facile colloidal layer-by-layer deposition of amorphous AlOx is applied on the CsPbBr3 perovskite nanocrystals (PNCs). The CsPbBr3 PNCs show improved photoluminescence intensity and excellent wat...

Highly Efficient CsPbBr3 Perovskite Nanocrystal Light-Emitting Diodes with Enhanced Stability via Colloidal Layer-by-Layer Deposition

Perovskite quantum dots light-emitting diodes (PQLEDs) usually suffer from low efficiency due to the imbalanced carrier injection. Dual hole injection layers (HILs) with NiOx/polyethylene dioxythiophene:polystyrene sulfonate are applied to tune the carrier transport and recombination in fabricated PQLEDs. The fine control of the NiOx film enables the external quantum efficiencies of the PQLEDs to increase from 1.5% to 9.7%, and the lifetime of T50 at 400 cd/m2 is prolonged by about 13 times with the cooperation of dual HIL. The improved performance of PQLEDs is attributed to the achievement of favorable carrier transport balance and effective radiative recombination in the emission layer. We highlight the critical role of carriers balance via the HIL engineering on both the efficiency and stability of PQLEDs. 

Boosted efficiency and lifetime of perovskite quantum dots light-emitting diode via NiOx/PEDOT:PSS dual hole injection layers

Electron transport layers (ETLs) are important components of high-performance all-inorganic perovskite nanocrystals light-emitting diodes (PNCs-LED). Herein, atomic layer deposition (ALD) of inorganic ZnO layer is combined to the organic 1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) to form dual ETLs to enhance both the efficiency and stability of PNCs-LED simultaneously. Optimization of ZnO thickness suggested that 10 cycles ALD yields the best performance of the devices. The external quantum efficiency of the device reaches to 7.21% with a low turn-on voltage (2.4 V). Impressively, the dual ETL PNCs-LED realizes maximum T 50 lifetime of 761 h at the initial luminance of 100 nit, which is one of the top lifetimes among PNCs-LEDs up to now. The improved performance of dual ETL PNCs-LED is mainly due to the improved charge transport balance with favorable energy level matching. These findings present a promising strategy to modify the function layer via ALD to achieve both highly efficient and stable PNCs-LED.

Fabrication of ZnO dual electron transport layer via atomic layer deposition for highly stable and efficient CsPbBr3 perovskite nanocrystals light-emitting diodes

Le Qin

Papers

Cu2+-Doped CsPbI3 Nanocrystals with Enhanced Stability for Light-Emitting Diodes.

Highly Efficient CsPbBr3 Perovskite Nanocrystal Light-Emitting Diodes with Enhanced Stability via Colloidal Layer-by-Layer Deposition

Boosted efficiency and lifetime of perovskite quantum dots light-emitting diode via NiOx/PEDOT:PSS dual hole injection layers

Fabrication of ZnO dual electron transport layer via atomic layer deposition for highly stable and efficient CsPbBr3 perovskite nanocrystals light-emitting diodes