Slow hot carrier (HC) cooling resulting from hot phonon bottleneck has been widely demonstrated in metal halide perovskites. Although manipulating HC kinetics in these materials is of both fundamental and technological importance, this task remains a daunting challenge. Here, via interfacial engineering, i.e., epitaxial growth of Cs 4 PbBr 6 on CsPbBr 3 nanocrystals (NCs), we have revealed an obvious shortening of HC cooling times, evidenced by transient absorption and ultrafast PL spectra. Collaborated with the longitudinal optical (LO) phonon model, theoretical calculations verify the breaking of the hot phonon bottleneck in CsPbBr 3 @Cs 4 PbBr 6 and identify the interfacial electron-LO phonon coupling as the leading mechanism for the observed large tuning of HC cooling times. Especially, the participation of LO phonons from Cs 4 PbBr 6 enables the efficient Klemens channel for hot phonon decay. Our findings establish an effective method to tailor HC dynamics in perovskite NCs, which could be conducive to improving the performance of optoelectronic applications.

Bi2O2Se, a high‐mobility and air‐stable 2D material, has attracted substantial attention for application in integrated logic electronics and optoelectronics. However, achieving an overall high performance over a wide spectral range for Bi2O2Se‐based devices remains a challenge. A broadband phototransistor with high photoresponsivity (R) is reported that comprises high‐quality large‐area (≈180 µm) Bi2O2Se nanosheets synthesized via a modified chemical vapor deposition method with a face‐down configuration. The device covers the ultraviolet (UV), visible (Vis), and near‐infrared (NIR) wavelength ranges (360–1800 nm) at room temperature, exhibiting a maximum R of 108 696 A W−1 at 360 nm. Upon illumination at 405 nm, the external quantum efficiency, R, and detectivity (D*) of the device reach up to 1.5 × 107%, 50055 A W−1, and 8.2 × 1012 Jones, respectively, which is attributable to a combination of the photogating, photovoltaic, and photothermal effects. The devices reach a −3 dB bandwidth of 5.4 kHz, accounting for a fast rise time (τrise) of 32 µs. The high sensitivity, fast response time, and environmental stability achieved simultaneously in these 2D Bi2O2Se phototransistors are promising for high‐quality UV and IR imaging applications.

Graphene has been widely investigated for use in high-performance photodetectors due to its broad absorption band and high carrier mobility. While exhibiting remarkably strong absorption in the ultraviolet range, the fabrication of a large-scale integrable, graphene-based ultraviolet photodetector with long-term stability has proven to be a challenge. Here, using graphene as a template for C assembly, we synthesized a large-scale all-carbon hybrid film with inherently strong and tunable UV aborption. Efficient exciton dissociation at the heterointerface and enhanced optical absorption enables extremely high photoconductive gain, resulting in UV photoresponsivity of ∼10 A/W. Interestingly, due to the electron-hole recombination process at the heterointerface, the response time can be modulated by the gate voltage. More importantly, the use of all-carbon hybrid materials ensures robust operation and further allows the demonstration of an exemplary 5 × 5 (2-dimensional) photodetector array. The devices exhibit negligible degradation in figures of merit even after 2 month of operation, indicating excellent environmental robustness. The combination of high responsivity, reliability, and scalable processability makes this new all-carbon film a promising candidate for future integrable optoelectronics.

All-inorganic mixed hybrid halide micro-platelet single crystals were fabricated and the photoinduced ion migration mechanism was investigated.

Due to strong Coulomb interactions, two-dimensional (2D) semiconductors can support excitons with large binding energies and complex many-particle states. Their strong light-matter coupling and emerging excitonic phenomena make them potential candidates for next-generation optoelectronic and valleytronic devices. The relaxation dynamics of optically excited states are a key ingredient of excitonic physics and directly impact the quantum efficiency and operating bandwidth of most photonic devices. Here, we summarize recent efforts in probing and modulating the photocarrier relaxation dynamics in 2D semiconductors. We classify these results according to the relaxation pathways or mechanisms they are associated with. The approaches discussed include both tailoring sample properties, such as the defect distribution and band structure, and applying external stimuli such as electric fields and mechanical strain. Particular emphasis is placed on discussing how the unique features of 2D semiconductors, including enhanced Coulomb interactions, sensitivity to the surrounding environment, flexible van der Waals (vdW) heterostructure construction, and non-degenerate valley/spin index of 2D transition metal dichalcogenides (TMDs), manifest themselves during photocarrier relaxation and how they can be manipulated. The extensive physical mechanisms that can be used to modulate photocarrier relaxation dynamics are instrumental for understanding and utilizing excitonic states in 2D semiconductors.

No abstract

With their strong light-matter interaction and rich photo-physics, two-dimensional (2D) transition metal dichalcogenides (TMDs) are important candidates for novel photonic and spin-valleytronic devices. It is highly desirable to control the photocarrier behaviours of monolayer TMDs to suit the needs of device functionalities. Here, through interfacial engineering, i.e., by depositing monolayer MoSe 2 onto different oxide substrates (SiO 2 , Al 2 O 3 and HfO 2 ), we have revealed large tuning of the exciton relaxation times in monolayer TMDs. Significantly, the non-radiative recombination of MoSe 2 is found shortened by almost one order of magnitude, from 160 ± 10 ps (on SiO 2 ) to 20 ± 4 ps (on HfO 2 ). Theoretical simulations based on ab initio non-adiabatic molecular dynamics (NAMD) method, together with temperature-dependent optical spectroscopy, identifies interfacial electron-phonon (e-ph) coupling as the leading mechanism for the lifetime tuning. Our results establish interface engineering as an effective knob for manipulating excited-state dynamics of monolayer TMDs.

Van der Waals (vdW) heterostructures constructed with two-dimensional (2D) materials have attracted great interests, due to their fascinating properties and potential for novel applications. While earlier efforts have advanced the understanding of the ultrafast cross-layer charge transfer process in 2D heterostructures, mechanisms for the interfacial photocarrier recombination remain, to a large extent, unclear. Here, we investigate a heterostructure comprised of black phosphorus (BP) and molybdenum disulfide (MoS2), with a type-II band alignment.Interestingly, it is found that the photo-generated electrons in MoS2 (transferred from BP) exhibit an ultrafast lifetime of ~5 ps, significantly shorter than those of the 2 constituent materials. By corroborating with the relaxation of photo-excited holes in BP, it is revealed that the ultrafast time constant is as a result of efficient Langevin recombination, where the high hole mobility of BP facilitates a large recombination coefficient (~2 × 10 −10 m 2 /s). In addition, broadband transient absorption spectroscopy confirms that the hot electrons transferred to MoS2 distribute over a broad energy range following an ultrafast thermalization. The rate of the interlayer Langevin recombination is found to exhibit no energy level dependence. Our findings provide essential insights into the fundamental photo-physics in type-II 2D heterostructures, and also provide useful guidelines for customizing photocarrier lifetimes of BP for high-speed photo-sensitive devices.