Kazunari Matsuda

Near-field photoluminescence imaging spectroscopy of naturally occurring GaAs quantum dots (QDs) is presented. We successfully mapped out center-of -mass wave functions of an exciton confined in a GaAs QD in real space due to the enhancement of spatial resolution up to 30 nm. As a consequence, we discovered that the spatial profile of the exciton emission, which reflects the shape of a monolayer-high island, differs from that of biexciton emission, due to different distributions of the polarizat

Transition-metal dichalcogenides exhibit great potential as active materials in optoelectronic devices because of their characteristic band structure. Here, we demonstrated that the photovoltaic performances of graphene/Si Schottky junction solar cells were significantly improved by inserting a chemical vapor deposition (CVD)-grown, large MoS2 thin-film layer. This layer functions as an effective electron-blocking/hole-transporting layer. We also demonstrated that the photovoltaic properties are

Nano-carbon materials (carbon nanotubes, graphene, and graphene oxide) have potential application for photovoltaics because of their excellent optical and electronic properties. Here, we demonstrate that a single-walled carbon nanotubes/graphene oxide buffer layer greatly improves the photovoltaic performance of organo-lead iodide perovskite solar cells. The carbon nanotubes/graphene oxide buffer layer works as an efficient hole transport/electron blocking layer. The photovoltaic conversion effi

We studied the mechanism of the photoluminescence (PL) enhancement and quenching of single CdSe∕ZnS nanocrystals on rough Au surfaces. Single nanocrystal spectroscopy revealed that the PL enhancement depends strongly on the excitation wavelength and liner-polarization angle due to the localized plasmon excitation and is also sensitive to the nanocrystal size. The polarization- and size-dependent PL enhancement and quenching are determined by the balance between the resonant energy transfer from

Abstract Artificial van der Waals heterostructures of 2D layered materials are attractive from the viewpoint of the possible discovery of new physics together with improved functionalities. Stacking various combinations of atomically thin semiconducting transition metal dichalcogenides, MX 2 (M = Mo, W; X = S, Se, Te) with a hexagonal crystal structure, typically leads to the formation of a staggered Type II band alignment in the heterostructure, where electrons and holes are confined in differe

We studied the temperature and excitation intensity dependence of exciton luminescence in individual single-walled carbon nanotubes (SWNTs) using single nanotube photoluminescence (PL) spectroscopy. The linear temperature dependence of the PL linewidth in a single SWNT implies that the exciton dephasing is dominated by the interaction between the exciton and the phonon mode with very low energy under lower-excitation conditions. Saturation of the PL intensity and broadening of the PL linewidth i

Layered materials, such as graphene, transition metal dichalcogenides and black phosphorene, have been established rapidly as intriguing building blocks for optoelectronic devices. Here, we introduce highly polarization sensitive, broadband, and high-temperature-operation photodetectors based on multilayer germanium sulfide (GeS). The GeS photodetector shows a high photoresponsivity of about 6.8 × 10³ A W^-1, an extremely high specific detectivity of 5.6 × 10¹⁴ Jo

We describe photoluminescence (PL), PL excitation, and time-resolved PL spectroscopy of hetero-bilayers comprising monolayers (1L) of MoS₂ and MoSe₂ at cryogenic temperatures. A PL peak showing a decay time of 2.5 ns was observed below 100 K, which can be attributed to an inter-layer exciton emission in the 1L-MoS₂/1L-MoSe₂ hetero-bilayers. An inter-layer exciton binding energy of ∼90 meV is determined from its thermal dissociation behavior; the band o

Abstract Perovskite solar cells (PSCs) have attracted intensive attention as the most promising next‐generation photovoltaic technology because they both enable accelerated development of photovoltaic performance and are compatible with low‐cost fabrication methods. The strategy of interface engineering of the perovskite layer in PSCs is expected to result in further enhancement of the power conversion efficiency (PCE) of PSCs via minimizing the charge recombination loss. Here, a high current–vo

We have studied the spectral homogeneous broadening of self-assembled ${\mathrm{In}}_{0.5}{\mathrm{Ga}}_{0.5}\mathrm{As}$ single quantum dots in a high-temperature regime with a highly sensitive near-field scanning optical microscope. Through precise examination of the photoluminescence spectra under weak excitation conditions, the homogeneous linewidth of the quantum dot was estimated to be about 12 meV at 300 K. We also found that the homogeneous linewidth changes with the interlevel spacing e

We have studied the optical properties of self-assembled In0.5Ga0.5As single quantum dots (QDs) at room temperature with a near-field scanning optical microscope. Successful detection of a weak photoluminescence (PL) signal from a single QD at room temperature could be achieved by using a double-tapered fiber probe having the advantages of both high collection efficiency and high spatial resolution. Through the precise examination of PL spectra of many QDs, including broadening and saturation be

We described the photoluminescence (PL) properties of individual micelle-encapsulated single-walled carbon nanotubes (SWNTs) at room temperature. Single PL peak from isolated individual SWNT with a chiral index of (6, 5) showed a linear increase and saturation behavior of the PL intensity. Unusual PL intensity fluctuation in the temporal evolutions of the PL intensity, referred to as PL intermittency, was seen with some SWNTs, while the PL intensity with most SWNTs remained at a constant amplitu

High-resolution photoluminescence (PL) imaging of semiconductor quantum dots (QDs) was demonstrated using a low-temperature near-field scanning optical microscope. We systematically evaluated the spatial resolution for various fiber probes with different aperture diameters ranging from 30 to 135 nm. We achieved a spatial resolution of 30 nm (∼λ/30:λ=930 nm) in the PL imaging of self-assembled InAs QDs due to both improvement in probe preparation and optimization of the sample structure. The spat

Abstract Atomically thin‐layered ReS 2 with a distorted 1 T structure has attracted attention because of its intriguing optical and electronic properties. Here, the direct and indirect exciton dynamics of a three‐layered ReS 2 is investigated by polarization‐resolved transient photoluminescence (PL) and ultrafast pump‐probe spectroscopy. The various time scales of the decay signals of the time‐resolved PL (<10 ps), with monitoring of the populations of electron–hole pairs (exciton), and the t

Perovskite solar cells (PSCs) using metal electrodes have been regarded as promising candidates for next-generation photovoltaic devices because of their high efficiency, low fabrication temperature, and low cost potential. However, the complicated and rigorous thermal deposition process of metal contact electrodes remains a challenging issue for reducing the energy pay-back period in commercial PSCs, as the ubiquitous one-time use of a contact electrode wastes limited resources and pollutes the