Subwavelength-Polarized Quasi-Two-Dimensional Perovskite Single-Mode Nanolaser.

When approaching the subwavelength or deep subwavelength scale, there is a fundamental trade-off between the ultimate shrinking size and the performance for miniaturized lasers. Herein, to overcome this trade-off, we investigated the excitonic gain nature of quasi-two-dimensional (quasi-2D) perovskites and revealed that both singlet excitons and polarons would make nearly the entire contribution within ∼50 ps to a high net gain of 558 cm-1. Inspired by the gain characteristic, we successfully shrank the quasi-2D perovskites laser to the subwavelength scale using only a layer of ultraviolet glue and a glass substrate in the vertical dimension. In spite of the compact and simple cavity structure, single-mode lasing with a highly linear polarization degree of 81% and a quality factor of 1635 was achieved. The extremely short cavity, excellent lasing performance, and simple structure of the quasi-2D perovskite laser are expected to provide insights into next-generation integrated laser sources.

Ultrafast Charge Generation Enhancement in Nanoscale Polymer Solar Cells with DIO Additive.

We study the ultrafast photoexcitation dynamics in PBDTTT-C-T (P51, poly(4,8-bis(5-(2-ethylhexyl)-thiophene-2-yl)-benzo[1,2-b:4,5-b']dithiophene-alt-alkylcarbonyl-thieno[3,4-b]thiophene)) film (~100 nm thickness) and PBDTTT-C-T:PC71BM (P51:PC71BM, phenyl-C71-butyric-acid-methyl ester) nanostructured blend (∼100 nm thickness) with/without DIO(1,8-diiodooctane) additives with sub-10 fs transient absorption (TA). It is revealed that hot-exciton dissociation and vibrational relaxation could occur in P51 with a lifetime of ~160 fs and was hardly affected by DIO. However, the introduction of DIO in P51 brings a longer lifetime of polaron pairs, which could make a contribution to photocarrier generation. In P51:PC71BM nanostructured blends, DIO could promote the Charge Transfer (CT) excitons and free charges generation with a ~5% increasement in ~100 fs. Moreover, the dissociation of CT excitons is faster with DIO, showing a ~5% growth within 1 ps. The promotion of CT excitons and free charge generation by DIO additive is closely related with active layer nanomorphology, accounting for Jsc enhancement. These results reveal the effect of DIO on carrier generation and separation, providing an effective route to improve the efficiency of nanoscale polymer solar cells.

Stable and enhanced frequency up-converted lasing from CsPbBr3 quantum dots embedded in silica sphere.

Perovskites have emerged as a class of cutting-edge light-emitting materials; however, their poor stability, due to the high sensitivity to moisture in the ambient environment, severely hinders their further application. Here, to obtain stable perovskite-based laser with excellent optical performance, all-inorganic perovskite CsPbBr3 quantum dots (QDs) evenly distributed into sub-micro silica sphere (CsPbBr3-SiO2) have been used as laser gain medium. The single silica sphere embedded by plentiful CsPbBr3 QDs demonstrates frequency up-converted lasing with compounded mode of random and whispering-gallery-mode (WGM) at room temperature. Furthermore, by incorporating the CsPbBr3-SiO2 spheres into a microtubule, the frequency up-converted WGM lasing has been successfully achieved under two-photon excitation. Notably, the CsPbBr3-SiO2 microtubule resonator exhibits a low lasing threshold of 430 µJ/cm2, mostly due to the enhanced gain for CsPbBr3 QDs inside the silica sphere. Moreover, stable WGM lasing is observed under continuous optical pump for 140 min, benefited from the protection of silica shells, which isolate the QDs from the environmental conditions. The enhanced lasing performance provides an effective way for further exploration and application of perovskite-based micro/nano photonic devices.

Ultrathin, Core-Shell Structured SiO2 Coated Mn2+ -Doped Perovskite Quantum Dots for Bright White Light-Emitting Diodes.

All-inorganic semiconductor perovskite quantum dots (QDs) with outstanding optoelectronic properties have already been extensively investigated and implemented in various applications. However, great challenges exist for the fabrication of nanodevices including toxicity, fast anion-exchange reactions, and unsatisfactory stability. Here, the ultrathin, core-shell structured SiO2 coated Mn2+ doped CsPbX3 (X = Br, Cl) QDs are prepared via one facile reverse microemulsion method at room temperature. By incorporation of a multibranched capping ligand of trioctylphosphine oxide, it is found that the breakage of the CsPbMnX3 core QDs contributed from the hydrolysis of silane could be effectively blocked. The thickness of silica shell can be well-controlled within 2 nm, which gives the CsPbMnX3 @SiO2 QDs a high quantum yield of 50.5% and improves thermostability and water resistance. Moreover, the mixture of CsPbBr3 QDs with green emission and CsPbMnX3 @SiO2 QDs with yellow emission presents no ion exchange effect and provides white light emission. As a result, a white light-emitting diode (LED) is successfully prepared by the combination of a blue on-chip LED device and the above perovskite mixture. The as-prepared white LED displays a high luminous efficiency of 68.4 lm W-1 and a high color-rendering index of Ra = 91, demonstrating their broad future applications in solid-state lighting fields.

Ultrastable CsPbBr3 Perovskite Quantum Dot and Their Enhanced Amplified Spontaneous Emission by Surface Ligand Modification.

The poor stability and aggregation problem of CsPbBr3 quantum dots (QDs) in air are great challenges for their future practical application. Herein, a simple and effective ligand-modification strategy is proposed by introducing 2-hexyldecanoic acid (DA) with two short branched chains to replace oleic acid (OA) with long chains during the synthesis process. These two short branched chains not only maintain their colloidal stability but also contribute to efficient radiative recombination. The calculations show that CsPbBr3 QDs with DA modification (CsPbBr3 -DA QDs) have larger binding energy than CsPbBr3 QDs with OA (CsPbBr3 -OA QDs), resulting in significantly enhanced stability. Due to the strong binding energy between DA ligands and QDs, CsPbBr3 -DA QDs exhibit no aggregation phenomenon even after stored in air for more than 70 d, and CsPbBr3 -DA QDs films can maintain 94.3% of initial PL intensity after 28 d, while in CsPbBr3 -OA QDs films occurs a rapid degradation of PL intensity. Besides, the enhanced amplified spontaneous emission (ASE) performance of CsPbBr3 -DA QDs films has been demonstrated under both one- and two-photon laser excitation. The ASE threshold of CsPbBr3 -DA QDs films is reduced by more than 50% and their ASE photostability is also improved, in comparison to CsPbBr3 -OA QDs films.

Highly Stable Silica-Wrapped Mn-Doped CsPbCl3 Quantum Dots for Bright White Light-Emitting Devices.

As an outstanding less-Pb candidate, doping Mn2+ ions into perovskite quantum dots (QDs) has received significant interest in the application of light-emitting diodes (LEDs). However, their further applications are impeded by poor chemical instability. Here, the silica-wrapped Mn-doped CsPbCl3 QDs are fabricated via hydrolyzing (3-aminopropyl) triethoxysilane with improved operational stability. Also, the photoluminescence quantum yield as high as 55.4% for the CsPbMnCl3@SiO2 composite is achieved. Silica wrapping can protect the perovskite QDs from damage by temperature and humidity as well as anion exchange. Furthermore, white LED devices are prepared by employing the mixture of green CsPbBr3 QDs and orange-red CsPbMnCl3@SiO2 composites. The as-obtained white LED device operated at a forward current of 20 mA exhibits bright natural light with a high luminous efficiency of 77.59 lm/W, and the corresponding color rendering index of 82 and color temperature (CCT) of 3950 K are obtained. Additionally, the electroluminescence spectrum shows nearly no variation after 24 h operation. This work will promote the Mn-doped CsPbCl3 QDs material to the practical application in solid-state LEDs.

Robust Subwavelength Single-Mode Perovskite Nanocuboid Laser.

On-chip photonic information processing systems require great research efforts toward miniaturization of the optical components. However, when approaching the classical diffraction limit, conventional dielectric lasers with all dimensions in nanoscale are difficult to realize due to the ultimate miniaturization limit of the cavity length and the extremely high requirement of optical gain to overcome the cavity loss. Herein, we have succeeded in reducing the laser size to subwavelength scale in three dimensions using an individual CsPbBr3 perovskite nanocuboid. Even though the side length of the nanocuboid laser is only ∼400 nm, single-mode Fabry-Pérot lasing at room temperature with laser thresholds of 40.2 and 374 µJ/cm2 for one- and two-photon excitation has been achieved, respectively, with the corresponding quality factors of 2075 and 1859. In addition, temperature-insensitive properties from 180 to 380 K have been demonstrated. The physical volume of a CsPbBr3 nanocuboid laser is only ∼0.49λ3 (where λ is the lasing wavelength in air). Its three-dimensional subwavelength size, excellent stable lasing performance at room temperature, frequency up-conversion ability, and temperature-insensitive properties may lead to a miniaturized platform for nanolasers and integrated on-chip photonic devices in nanoscale.

Ultrafast dynamics of multi-exciton state coupled to coherent vibration in zinc chlorin aggregates for artificial photosynthesis.

Ultrafast vibronic dynamics induced by the interaction of the Frenkel exciton with the coherent molecular vibrations in a layer-structured zinc chlorin aggregates prepared for artificial photosynthesis have been studied by 7.1 fs real-time vibrational spectroscopy with multi-spectrum detection. The fast decay of 100 ± 5fs is ascribed to the relaxation from the higher multi-exciton state (MES) to the one-exciton state, and the slow one of 863 ± 70fs is assigned to the relaxation from Q-exciton state to the dark nonfluorescent charge-transfer (CT) state, respectively. In addition, the wavelength dependences of the exciton-vibration coupling strength are found to follow the zeroth derivative of the transient absorption spectra of the exciton. It could be explained in term of the transition dipole moment modulated by dynamic intensity borrowing between the B transition and the Q transition through the vibronic interactions.