Browsing by Author "Nakamura, Keisuke"

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Arbitrary control of the diffusion potential between a plasmonic metal and a semiconductor by an angstrom-thick interface dipole layer
(2020-01-21)
Oshikiri, Tomoya
;
Sawayanagi, Hiroki
;
Nakamura, Keisuke
;
Ueno, Kosei
;
Katase, Takayoshi
Localized surface plasmon resonances (LSPRs) are gaining considerable attention due to the unique far-field and near-field optical properties and applications. Additionally, the Fermi energy, which is the chemical potential, of plasmonic nanoparticles is one of the key properties to control hot-electron and -hole transfer at the interface between plasmonic nanoparticles and a semiconductor. In this article, we tried to control the diffusion potential of the plasmonic system by manipulating the interface dipole. We fabricated solid-state photoelectric conversion devices in which gold nanoparticles (Au-NPs) are located between strontium titanate (SrTiO3) as an electron transfer material and nickel oxide (NiO) as a hole transport material. Lanthanum aluminate as an interface dipole layer was deposited on the atomic layer scale at the three-phase interface of Au-NPs, SrTiO3, and NiO, and the effect was investigated by photoelectric measurements. Importantly, the diffusion potential between the plasmonic metal and a semiconductor can be arbitrarily controlled by the averaged thickness and direction of the interface dipole layer. The insertion of an only one unit cell (uc) interface dipole layer, whose thickness was less than 0.5 nm, dramatically controlled the diffusion potential formed between the plasmonic nanoparticles and surrounding media. This is a new methodology to control the plasmonic potential without applying external stimuli, such as an applied potential or photoirradiation, and without changing the base materials. In particular, it is very beneficial for plasmonic devices in that the interface dipole has the ability not only to decrease but also to increase the open-circuit voltage on the order of several hundreds of millivolts.
Cobalt Oxide (CoOx) as an Efficient Hole-Extracting Layer for High Performance Inverted Planar Perovskite Solar Cells
(2016-12-14)
Shalan, Ahmed Esmail
;
Oshikiri, Tomoya
;
Narra, Sudhakar
;
Elshanawany, Mahmoud M.
;
Ueno, Kosei
CoOx is a promising hole-extracting layer (HEL) for inverted planar perovskite solar cells with device configuration ITO/CoOx/CH3NH3PbI3/PCBM/Ag. The devices fabricated according to a simple solution procedure showed the best photovoltaic performance attaining power conversion efficiency (PCE) of 14.5% under AM 1.5 G 1 sun irradiation, which is significantly superior to those of materials fabricated with a traditional HEL such as PEDOT:PSS (12.2%), NiOx (10.2%), and CuOx (9.4%) under the same experimental conditions. We characterized the chemical compositions with XPS, crystal structures with XRD, and film morphology with SEM/AFM techniques. Photoluminescence (PL) spectra and the corresponding PL decays for perovskite deposited on varied HEL films were recorded to obtain the hole-extracting characteristics, for which the hole extracting times show the order CoOx (2.8 ns) < PEDOT:PSS (17.5 ns) < NiOx (22.8 ns) < CuOx (208.5 ns), consistent with the trend of their photovoltaic performances. The reproducibility and enduring stability of those devices were examined to show the outstanding long-term stability of the devices made of metal oxide HEL, for which the CoOx device retained PCE approximate to 12% for over 1000 h.
Plasmon-Assisted Polarity Switching of a Photoelectric Conversion Device by UV and Visible Light Irradiation
(2018-06-28)
Nakamura, Keisuke
;
Oshikiri, Tomoya
;
Ueno, Kosei
;
Katase, Takayoshi
;
Ohta, Hiromichi
The plasmon-induced charge separation between metallic nanoparticles and a semiconductor following an electron transfer process has been extensively studied as one of the mechanisms in plasmonic light energy conversion devices. In this study, we propose that the switching of photocurrent polarity can be realized by changing the rectification properties of plasmonic photoelectric conversion devices and utilizing the difference in carrier mobility between electrons and holes. We fabricated plasmonic photoelectric conversion devices using gold nanoparticles (Au-NPs), nickel oxide (NiO), and mobility-limited TiO2 (ML-TiO2) to control the photocurrent polarity according to irradiation wavelengths of visible and UV light. A pulsed laser deposition technique was employed to deposit the ML-TiO2 and NiO layers. The photoelectric properties were measured, and in situ spectroelectrochemical measurements were performed to investigate the relationship between the rectification properties of the plasmonic photoelectric conversion devices and the change in the Fermi level of the Au-NPs under UV light irradiation condition. Additionally, UV and visible light irradiation selectively induced the current of opposite polarity with the small applied voltage. The electron transfer phenomena from ML-TiO2 to Au-NPs and from Au-NPs to ML-TiO2 give us important information to understand plasmon-related charge separation.
Properties of Plasmon-Induced Photoelectric Conversion on a TiO2/NiO p-n Junction with Au Nanoparticles
(2016-03-17)
Nakamura, Keisuke
;
Oshikiri, Tomoya
;
Ueno, Kosei
;
Wang, Yongming
;
Kamata, Yoshiomi
We have successfully fabricated all-solid-state plasmonic photoelectric conversion devices composed of titanium dioxide (TiO2)/nickel oxide (NiO) p-n junctions with gold nanoparticles (Au-NPs) as prototype devices for a plasmonic solar cell. The characteristics of the crystal structures and the photoelectric properties of the all-solid-state devices were demonstrated. We observed that the crystalline structure of the NiO thin film and the interfacial structure of TiO2/Au-NPs/NiO changed significantly during an annealing treatment. Furthermore, the photoelectric conversion devices exhibited plasmon-induced photocurrent generation in the visible-wavelength region. The photo current may result from plasmon-induced charge separation. The photoelectric conversion properties via plasmon-induced charge separation were strongly correlated with the morphology of the TiO2/Au-NPs/NiO interface. The long-term stability of the plasmonic photoelectric conversion device was found to be very high because a stable photocurrent was observed even after irradiation for 3 days.
Versatile plasmonic-effects at the interface of inverted perovskite solar cells
(2017)
Shalan, Ahmed Esmail
;
Oshikiri, Tomoya
;
Sawayanagi, Hiroki
;
Nakamura, Keisuke
;
Ueno, Kosei
Plasmonics is a highly promising approach to enhancing the light-harvesting properties of hybrid organic/ inorganic perovskite solar cells. In the present work, our cells have a p-i-n inverted planar structure. An ultrathin NiO film with two different thicknesses of 5 and 10 nm prepared by a pulsed laser deposition process on an ITO substrate with a faceted and furrowed surface enabled the formation of a continuous and compact layer of well-crystallized CH3NH3PbI3 via an anti-solvent chlorobenzene process. The coverage mechanism of the NiO film on the ITO was clearly demonstrated through the J-V and external quantum efficiency (EQE) curves. Moreover, the results demonstrated that the gold nanoislands (Au NIs) increased the power conversion efficiency to 5.1%, almost double that of the samples without Au NIs. This result is due to the excitation of surface plasmons, which is characterized by strong scattering and enhancement of the electric field in the vicinity of the Au NIs loaded at the interface between the NiO and perovskite films. Additionally, we observed an enhancement of the EQE at wavelengths shorter than the plasmon resonance peak. In the current state, we speculate that the plasmoelectric potential effect is considered to be a good explanation of the photocurrent enhancement at the off-resonance region. Our work provides good guidance for the design and fabrication of solar-energy-related devices employing NiO electrodes and plasmonic Au NIs.
Versatile plasmonic-effects at the interface of inverted perovskite solar cells
(2017)
Shalan, Ahmed Esmail
;
Oshikiri, Tomoya
;
Sawayanagi, Hiroki
;
Nakamura, Keisuke
;
Ueno, Kosei
Plasmonics is a highly promising approach to enhancing the light-harvesting properties of hybrid organic/ inorganic perovskite solar cells. In the present work, our cells have a p-i-n inverted planar structure. An ultrathin NiO film with two different thicknesses of 5 and 10 nm prepared by a pulsed laser deposition process on an ITO substrate with a faceted and furrowed surface enabled the formation of a continuous and compact layer of well-crystallized CH3NH3PbI3 via an anti-solvent chlorobenzene process. The coverage mechanism of the NiO film on the ITO was clearly demonstrated through the J-V and external quantum efficiency (EQE) curves. Moreover, the results demonstrated that the gold nanoislands (Au NIs) increased the power conversion efficiency to 5.1%, almost double that of the samples without Au NIs. This result is due to the excitation of surface plasmons, which is characterized by strong scattering and enhancement of the electric field in the vicinity of the Au NIs loaded at the interface between the NiO and perovskite films. Additionally, we observed an enhancement of the EQE at wavelengths shorter than the plasmon resonance peak. In the current state, we speculate that the plasmoelectric potential effect is considered to be a good explanation of the photocurrent enhancement at the off-resonance region. Our work provides good guidance for the design and fabrication of solar-energy-related devices employing NiO electrodes and plasmonic Au NIs.