Search

In semiconductor‐based microlasers, the generated excited carriers can affect both the optical absorption coefficient and refractive index, influencing the lasing behavior and device performance. In this study, the lasing behavior of individual MAPbBr3 microrods pumped by femtosecond laser pulses is investigated using an ultrafast optical Kerr gating technique. By analyzing the spectral and temporal evolution of the lasing behavior, it is found that the band‐filling (BF) effect can cause a significant change in the refractive index of the material, which results in an unfavorable red‐shift and broadening of the resonant modes, deteriorating the laser linewidth and quality factor. The hot carrier cooling process can provide a buffer for alteration of the energy level occupation state, resulting in a small transient refractive index change and slight red‐shift. These results offer insights into the lasing behavior driven by photogenerated carrier dynamics and provide an optimization strategy for semiconductor‐based microlasers. [ABSTRACT FROM AUTHOR]

Germanium diselenide (GeSe2) has recently emerged as a promising material for high‐performance optoelectronic devices due to its high absorption coefficient, wide direct bandgap, and anisotropic electronic properties. For the future applications, it is necessary to understand the dynamic evolution of carriers with ultrafast response. In this work, the transient absorption spectroscopy measurements are performed to study the anisotropic dynamic evolution of GeSe2 under the polarized photoexcitation. It is find that the dynamics exhibit linear dichroism and show a significant Auger recombination process when the photoexcitation is perpendicular to the b‐axis of GeSe2. Using first‐principle and transition dipole moment calculations, it is confirmed that the more carrier localization at Γ point along the Γ‐X (perpendicular to the b‐axis) and increase the Auger recombination. In addition, the Auger recombination coefficient ≈ 1.1×10−31 cm6 s−1 is determined and demonstrated that the defect‐assisted indirect Auger recombination plays a key role in the carrier relaxation process. Through time‐resolved transient absorption spectra, it is further revealed that the ultrafast dynamical evolution of excited state absorption peaks under polarized photoexcitation. These results have implications for improving the quantum efficiency of high‐field polarization‐sensitive optoelectronics. [ABSTRACT FROM AUTHOR]

We demonstrate an environmentally stable femtosecond laser for industrial application based on all polarization‐maintaining Yb‐doped laser and experimentally explore the effect of the net cavity dispersion (NCD) on output characteristics. The oscillator emits pulses with 5.1 ps and a 23 nm spectral bandwidth, then the pulse is compressed to 88 fs. The instabilities over 120 h gives 0.32% relative root mean square noise, indicating high stability of the pulse laser. With effective regulation of NCD, we obtained the maximum spectral bandwidth of 27 nm. Such broadband oscillator with compact all‐fiber configurations provide extremely high stability should be very attractive for long‐term industrial application. [ABSTRACT FROM AUTHOR]

Controlled sequential crystallization of donors and acceptors is a critical factor for achieving enhanced phase separation and efficient charge transfer performance in polymer solar cells (PSCs). In this study, a comprehensive investigation of a structurally simple solvent additive, 1‐fluoro‐2‐iodobenzene (OFIB) is conducted, which efficiently controls the morphology of the active layer, resulting in fibrous assembly and significantly enhancing the power conversion efficiency from 16.34% to 18.38% based on the PM6:L8‐BO system. Density functional theory, molecular dynamics simulations, and grazing incidence small‐ and wide‐angle X‐ray scattering techniques reveal that the addition of OFIB to the processed blend aligns the orientation of the acceptor molecules, thereby enhancing the overall π–π stacking in the active layer. OFIB establishes nearly equal‐strength π–π interactions with the conjugated frameworks of both the donor and acceptor materials, benefiting from the multiple electron conjugation between its iodine atom and the conjugated framework in the active layer. Femtosecond‐timescale photophysical studies demonstrate that the OFIB‐optimized active layer shows reduced exciton losses at the donor–acceptor interface. This study offers a new perspective on the mechanism underlying the function of solvent additives and presents a comprehensive research methodology that will guide the development of next‐generation non‐fullerene acceptors for efficient PSCs. [ABSTRACT FROM AUTHOR]

Single‐crystal halide perovskites are among the most promising semiconductor candidates for highly efficient optoelectronic devices due to their higher stability against moisture and light radiation and lower trap density than their polycrystalline counterparts. In this work, single‐crystal MAPbBr3 microcavities with controllable geometries and sizes are fabricated using a template‐limited method combined with an anti‐solvent diffusion growth method. The single‐crystal microcavities emit lasers around 550 nm under femtosecond laser excitation, with a lasing threshold of ≈35 µJ cm−2 and a quality factor of 1135, as well as excellent long‐term operation stability. The temporal‐spatial evolution of the lasing process in an individual microcavity is achieved by the microscopic optical Kerr‐gating technique. The temporal behaviors including pulse duration and build‐up time, emission spectra shift, and lasing mode evolution as a function of pump fluence are unveiled, and the complex relationship between the light‐induced carrier dynamics and lasing properties is clarified. Spatial heterogeneous lasing dynamics are also observed in an individual microdisk, which is attributed to the non‐uniform optical losses and carrier densities driven by structural imperfections. This study can provide a fabrication strategy for perovskite on‐chip optoelectronic devices, as well as a deeper understanding of the carrier‐density‐driven lasing dynamics in microcavities. [ABSTRACT FROM AUTHOR]

The advancement of carbon‐based electronics is reliant on the development of semiconducting carbon nanotubes with high purity and yield. We developed a new extraction strategy to efficiently sort SWCNTs with superior yields and purity. The approach uses two polymers, poly[N‐(1‐octylnonyl)‐9H‐carbazol‐2,7‐diyl](PCz) and poly(9,9‐n‐dihexyl‐2,7‐fluorene‐alt‐9‐phenyl‐3,6‐carbazole)(PDFP), and two sonication processes to eliminate surface polymer contamination. PCz selectively wraps large‐diameter s‐SWCNTs, with PDFP added as an enhancing molecule to increase sorting efficiency at 4‐fold compared to the efficiency of only PCz alone sorting. The purity of the sorted s‐SWCNTs was confirmed to be above 99 % using absorption and Raman spectra. Field‐effect transistors and photodetectors made from the sorted s‐SWCNTs exhibited excellent semiconductor properties and broad‐spectrum detection, with good long‐term stability. Furthermore, a photodetector using large‐tube diameter s‐SWCNTs achieved broad‐spectrum detection, which the photoresponsivity is 0.35 mA/W and the detectivity is 4.7×106 Jones. The s‐SWCNTs/graphene heterojunction photodetector achieved a photoresponsivity of 3 mA/W and a detectivity of 6.3×106 Jones. This new strategy provides a promising approach to obtain high‐purity and high‐yield s‐SWCNTs for carbon‐based photodetectors. [ABSTRACT FROM AUTHOR]

A comparative analysis of sorted semiconducting (sc‐) single‐walled carbon nanotubes (SWCNTs) films, metallic (m‐) SWCNTs films, pristine SWCNTs films, and graphene‐based simple two‐terminal sensors for the applications of ammonia gas sensing is presented. The comparison of the sensing response of different devices by separately measuring the SWCNTs film resistance and the contact resistance between SWCNTs and the electrodes reveals that the performance mainly relies on the modification of tube conductivity under exposure to gas. Moreover, the measurements show that the highest sensitivity of the devices is achieved by use of sc‐SWCNTs as the conducting channels. Sensor coated with surfactant‐free sc‐SWCNTs shows a sensitivity of 0.78% ppm at 5–100 ppm ammonia (NH3) concentrations that happened to be ≈28, ≈22, and ≈173 times more sensitive than pristine‐SWCNTs, m‐SWCNTs, and graphene‐based sensors, respectively, at 50 ppm and ≈4.5 times the previously reported sc‐SWCNTs‐based sensor at 5 ppm. Notably, all the experiments values are achieved at room temperature without any extra heating treatment for the recovery process. These results show that surfactant‐free sc‐SWCNTs provide a promising way of creating sensors with improved selectivity and sensitivity, which predicts the auspicious prospects in the development of future applications. [ABSTRACT FROM AUTHOR]

It is a challenging and application‐oriented goal to achieve the metal/semiconductor separation of large diameter single‐walled carbon nanotubes (SWCNTs) using a dextran‐based gel chromatograph. Herein, a study of the temperature effect on the metal/semiconductor separation of plasma torch SWCNTs through dextran‐based gel chromatograph is conducted. The temperature governs the interaction between SWCNTs and hydrogel, thus enabling the sorting of SWCNTs by electronic type. In addition, the temperature effect enables the metallic (m‐) and semiconducting (sc‐) fraction to be resolved and eluted using a single cosurfactant system, so that the process can be iterated easily. The fractions containing up to 99% of sc‐SWCNTs and 95% of m‐SWCNTs have been obtained after three times of iteration. The iteration process is not only applicable to sc‐SWCNTs and m‐SWCNTs, but also practicable for the cosurfactant system and circumvents additional preparation steps. [ABSTRACT FROM AUTHOR]

In this work, we report a new mixed‐extractor strategy to improve the sorting yield of large‐diameter semiconducting single‐walled carbon nanotubes (s‐SWCNTs) with high purity. In the new mixed‐extractor strategy, two kinds of conjugated polymers with different rigidity, poly(9,9‐n‐dihexyl‐2,7‐fluorene‐alt‐9‐phenyl‐3,6‐carbazole) (PDFP) and poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (P8BT), are used to sort large‐diameter s‐SWCNTs through two simple sonication processes. To our surprise, although PDFP itself shows no selectivity toward s‐SWCNTs, it can greatly enhance the sorting yield of P8BT. Using the PDFP/P8BT mixed‐extractor method, the yield of sorted s‐SWCNTs has been enhanced by 5 times with a purity above 99 % in comparison to that using P8BT single‐extractor method. In addition, the photoluminescence (PL) excitation maps shows that the PDFP/P8BT mixed‐extractor system not only enhances the sorting yield substantially, but also tends to be enrichment of (15,4) SWCNTs with the diameter of 1.36 nm. [ABSTRACT FROM AUTHOR]

All‐inorganic lead halide perovskite nanocrystals (NCs) have been widely applied in optoelectronic devices owing to their excellent photoluminescence (PL) properties. However, poor stability upon exposure to water, UV light or heat strongly limits their practical application. Herein, CsPbBr3@Pb‐MOF composites with exceptional stability against water, UV light, and heat are synthesized by ultrasonic processing the precursors of lead‐based MOF (Pb‐MOF), oleylammonium bromide (OAmBr) and cesium oleate (Cs‐OA) solutions at room temperature. Pb‐MOF can not only provide the lead source for the in situ growth of CsPbBr3 NCs, but also the protective layer of perovskites NCs. The formed CsPbBr3@Pb‐MOF composites show a considerable PL quantum yield (PLQY) of 67.8%, and can maintain 90% of the initial PL intensity when immersed in water for 2 months. In addition, the outstanding PL stability against UV light and heat is demonstrated with CsPbBr3 NCs synthesized by the conventional method as a comparison. Finally, a green (light‐emitting diode) LED is fabricated using green‐emitting CsPbBr3@Pb‐MOF composites and exhibits excellent stability without packaging when immersed in water for 30 days. This study provides a practical approach to improve the stability in aqueous phase, which may pave the way for future applications for various optoelectronic devices. [ABSTRACT FROM AUTHOR]