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Small bimolecular charge recombination coefficients resulted in all-polymer blend solar cells with high fill factors. The preferred blend morphology was characterized by a well-ordered local structure, exhibiting chain aggregation by both the polymer donor and acceptor.

PCPDTBT, a copolymer of cyclopentadithiophene and benzothiadiazole, is a locally ordered low-bandgap donor–acceptor conjugated polymer that has been used as a hole-transport material for polymer blend solar cells. In this study, the short-range order structure of PCPDTBT in spin-coated PCPDTBT/conjugated polymer blend films has been characterized to elucidate aggregation behaviors that arise when a locally ordered conjugated polymer is blended with other polymers. UV–vis absorption spectroscopy and grazing-incidence wide-angle X-ray scattering measurements revealed that short-range ordering of PCPDTBT is promoted when it is diluted in an amorphous conjugated polymer matrix, poly­(3-methyl-4-hexylthiophene-2,5-diyl) (P3M4HT). In a PCPDTBT/P3M4HT blend film with 10 wt % PCPDTBT, the fraction of PCPDTBT chains that form aggregates increases from 51% (in neat film) to 78%, and the correlation length of the ordered PCPDTBT chains extends from 4.6 nm (in neat film) to 7.7 nm in the chain backbone direction. The polymer matrix-assisted ordering can be explained in terms of suppression of both undesired overlap and interpenetration of PCPDTBT chains; both processes can derange the self-aggregated single-chain order of PCPDTBT. This short-range ordering enhancement would be significant for the design of efficient charge carrier transport in thin-film devices such as polymer/polymer blend solar cells that use low-bandgap donor–acceptor conjugated polymers with various blend ratios as hole- and electron-transport materials.

The terahertz (THz)-wave absorption properties in organic-inorganic hybrid perovskite (OHP) materials are investigated with the in-depth development of OHP-based THz applications. In the THz range from 0.5 to 3 THz, OHPs typically show several interesting phonon modes such as transverse, longitudinal, and halogen self-vibrations. To modulate these frequencies, the density changes in defect-incorporated structures and element mixtures were tested and confirmed. In the literature, the origin of phonon modes in OHP materials have been mostly explained. However, we found new phonon vibration modes in formamidinium (FA)-based hybrid perovskite structures. FAPbI3 single crystals, organic–inorganic hybrid perovskites, of the δ-, δ/α-mixed-, and α-phases were prepared. We intriguingly found that the δ/α-mixed-phase exhibited significant THz-wave absorption peaks at 2.0 and 2.2 THz that were not related to any phonon modes from either the δ- or α-phases, although the δ/α-mixed-phase sample was confirmed to be formed by a physical combination of the δ- and α-phases without the creation of any new chemical states. Our theoretical study performed with ab initio calculations provides an explanation for these unusual THz-wave absorption behaviors; they originate from the novel vibration modes excited at the seamless interfaces in the mixed phase of FAPbI3. We found new phonon vibration modes in formamidinium (FA)-based hybrid perovskite structures. We intriguingly found that the δ/α-mixed-phase exhibited significant THz-wave absorption peaks at 2.0 and 2.2 THz that were not related to any phonon modes from either the δ- or α-phases, although the δ/α-mixed-phase sample was confirmed to be formed by a physical combination of the δ- and α-phases without the creation of any new chemical states. From the theoretical study, they originate from the novel vibration modes excited at the seamless interfaces in the mixed phase of FAPbI3. New vibrational modes generated by low-cost organic–inorganic crystals could be of value for terahertz devices used for non-invasive cell and tissue imaging. Vibrationally excited molecules can often be identified from terahertz energy signals, but these signals are hard to detect with conventional electronics. Researchers led by Young-Kyun Kwon from Kyung Hee University in Seoul, South Korea, and Min-Cherl Jung at the University of Tsukuba in Ibaraki, Japan, report insights into how optically active materials known as hybrid perovskites can be engineered to improve terahertz detection. The team’s analysis of formamidinium-lead-iodide perovskites showed that new terahertz-sensitive modes could be seen when the material solidified into a crystal containing two different structural arrangements known as phases. Theoretical simulations revealed the modes appear because of vibrations generated at the phase interfaces.

To understand the origin of the irreproducibility of the hole injection barrier at the interface between Au top-contact electrodes and organic semiconductors, we performed a systematic study by focusing on the deposition rate of Au. As a benchmarking material system, we fabricated field-effect transistors with pentacene active layers and Au top-contact electrodes evaporated with the deposition rate from 0.5 to 10 A/s. From the contact potential differences (ΔCPDs) between Au and pentacene measured with Kelvin-probe force microscopy, cross-sectional structures with scanning transmission electron microscopy, crystallographic structures with X-ray diffraction, and Au depth profiles with secondary ion mass spectrometry, we concluded that the variation of ΔCPD is due to embedded Au nanoclusters in pentacene with the average diameter of 4–6 nm. These Au nanoclusters, of which depth significantly varies by the Au deposition rate, modulate the ΔCPD and interfere with the reproducibility of hole injection barrier. As a result, gate threshold voltage and field-effect mobility also become irreproducible.

To start a step such as some realization of minimized and integrated devices, it requires simply understanding the surface status of hybrid perovskite on the e-beam irradiation because many commercial semiconductor devices are performed with a surface patterning process using e-beam or etching gas. The surface status of CH3NH3PbBr3 (MAPbBr3) single crystal was studied after a grazing e-beam irradiation in an ultra-high vacuum. The prepared hybrid perovskite single crystal was irradiated by the 3 degree-grazing e-beam with energy of 15 kV for 10 min using a reflection high-electron energy diffraction technique. The e-beam irradiation on the MAPbBr3 hybrid perovskite single crystal induced the deformation from MAPbBr3 into MABr, Br2, and Pb on the surface. The gas phases of MABr and Br2 are depleted from the surface and the Pb element has remained on the surface. As a result of the e-beam irradiation, it formed a polycrystalline-like phase and Pb metal particles on the surface, respectively.

To control the density of a CH3NH2 molecular defect, which strongly contributed to a significant THz-wave absorption property in the CH3NH3PbI3 hybrid perovskite thin film formed by the sequential vacuum evaporation method, we performed post-annealing processes with various temperatures and times. In the thin film after post-annealing at 110 &deg, C for 45 min, the density of the CH3NH2 molecular defect was minimized, and CH3NH3I and PbI2 disappeared in the thin film after the post-annealing process at 150 &deg, C for 30 min. However, the density of the CH3NH2 molecular defect increased. Moreover, the THz-wave absorption property for each thin film was obtained using a THz time-domain spectroscopy to understand the correlation between the density of a molecular defect and the THz-wave oscillation strength at 1.6 THz, which originated in the molecular defect-incorporated hybrid perovskite structure. There is a strong linear correlation between the oscillator strength of a significant THz-wave absorption at 1.6 THz and the CH3NH2 molecular defect density.

To understand the instability of Sn-based perovskite, CH3NH3SnI3, photoelectron spectroscopy with synchrotron radiation and theoretical calculations, such as density functional theory and ab initio molecular dynamics, were performed. Findings from this experimental and theoretical study highlight the crucial changes of surface-chemical states, the broken chemical bondings in Sn–I, and the depletion of a CH3–NH3+ cation on the surface region. The material instability origin of Sn-based perovskite can be explained by the chemical state instability in the surface.

To improve the performance of organic photovoltaics (OPV) for energy harvesting from blue-light, the OPVs (Ag/BCP/C60/BPh-BTBT/10 mol% p-doped BPh-BTBT/ITO) are fabricated with several dopants such as F4TCNQ, C60F36, HATCN, and Mo(tfd)3. The power conversion efficiencies of the OPVs with F4TCNQ, C60F36, HATCN, and Mo(tfd)3-doped BPh-BTBT obtained by white light-emitting diode source are improved with 60, 78, 46, and 49% than those by normal solar light, respectively. Secondary ion mass spectroscopy is performed with the 1-day and 7-days samples after the sample fabrication to observe the dopant distributions in each p-doped layer. Diffusion of dopant is observed only in the F4TCNQ-doped BPh-BTBT.

Understanding the controllability of the THz-wave absorption property of organic–inorganic hybrid perovskite (OHP) thin films is necessary to advance the THz-based application field. Here, we found the correlation of THz-wave absorption property by different halogen elements in FAPb(Br, I)-based hybrid perovskite thin films fabricated by sequential vacuum evaporation. We confirm that the selection of halogen elements and their concentration ratio can be changed to systematically control the THz conductivity property.

Hole transport layers (HTL) are crucial materials to improve the power conversion efficiency in organohalide hybrid perovskite-based solar-cell applications. Two important physical properties are required in HTL materials: good hole mobility and air-protection. After HTL solution-based deposition, an intermixed chemical state at the interface between HTL and hybrid perovskite is key to confirming the physical property of HTL. We performed high-resolution x-ray photoelectron spectroscopy to investigate the chemical states at the interface between an ultra-thin P3 polymer and CH3NH3PbI3 hybrid perovskite thin film. At the interface, we found no apparent intermixed chemical state. Furthermore, we confirmed that the P3 HTL with the ultra-thin layer (7 nm) protected the hybrid perovskite material against air-exposure for 2 weeks.

The valid strong THz absorption at 1.58 THz was probed in the organic-inorganic hybrid perovskite thin film, CH3NH3PbI3, fabricated by sequential vacuum evaporation method. In usual solution-based methods such as 2-step solution and antisolvent, we observed the relatively weak two main absorption peaks at 0.95 and 1.87 THz. The measured absorption spectrum is analyzed by density-functional theory calculations. The modes at 0.95 and 1.87 THz are assigned to the Pb-I vibrations of the inorganic components in the tetragonal phase. By contrast, the origin of the 1.58 THz absorption is due to the structural deformation of Pb-I bonding at the grain boundary incorporated with a CH3NH2 molecular defect.

Hole transport layers (HTL) are crucial materials to improve the power conversion efficiency in organohalide hybrid perovskite-based solar-cell applications. Two important physical properties are required in HTL materials: good hole mobility and air-protection. After HTL solution-based deposition, an intermixed chemical state at the interface between HTL and hybrid perovskite is key to confirming the physical property of HTL. We performed high-resolution x-ray photoelectron spectroscopy to investigate the chemical states at the interface between an ultra-thin P3 polymer and CH3NH3PbI3 hybrid perovskite thin film. At the interface, we found no apparent intermixed chemical state. Furthermore, we confirmed that the P3 HTL with the ultra-thin layer (7 nm) protected the hybrid perovskite material against air-exposure for 2 weeks.

A CH3NH3PbBr3 (MAPbBr3) single crystal was subjected to 2 and 10 V biasing for 10 min under ultra-high vacuum to investigate the bias effect on the surface of MAPbBr3. Under these controlled conditions, we performed high-resolution photoelectron spectroscopy on the MAPbBr3 single crystals at photon energies of 460 and 100 eV under synchrotron radiation to obtain core-level and valence structure spectra. The CH3NH2 molecular defect relative intensity area ratio decreased from 22% to 10%. It was assumed that the bias effect can induce a low density of defect states to suppress large defect-pinned energy states at the interfaces.

In this work we performed dopant diffusion experiments on the hole transport material spiro-OMeTAD. Pure spiro-OMeTAD/F4-TCNQ doped spiro-OMeTAD and pure spiro-OMeTAD/DMC doped spiro-OMeTAD thin films were deposited on Au/Si(100) substrates. The energy levels, chemical states, and surface morphologies of formed films were studied by ultraviolet photoemission spectroscopy, x-ray photoelectron spectroscopy, and atomic force microscopy as a function of the storage time in ultrahigh vacuum. We found only the pure spiro-OMeTAD/DMC doped spiro-OMeTAD film showed the n-type doping with the Fermi level of the film shifting away from the HOMO edge by 0.3 eV after 36 h. We propose that the diffusion of DMC dopant leads to the increase of the efficiencies of perovskite solar cell with the pin-hole free n-i-p structured hole transport layer several days after fabrication.

We deposited lead-free CH3NH3SnBr3 – organometal halide perovskite films using two vapor deposition-based methods (i.e., co-evaporation and sequential evaporation) using SnBr2 and CH3NH3Br. We obtained comprehensive information about the structural and electronic properties of these Pb-free perovskite films. X-ray diffraction results confirmed the crystalline structure of MASnBr3. Using UV-Vis measurements, we determined the optical bandgap of these films to be ∼2.2 eV. On the basis of ultraviolet photoemission spectroscopy results, the work function and ionization energy were measured to be 4.3 and 6.1 eV, respectively. Solar cells employing such a perovskite film in a planar structure were fabricated with various hole transport layers (HTLs) (spiro-OMeTAD, C60, and P3HT). For perovskite films prepared by co-deposition, we obtained solar cell efficiencies ranging from 0.03 to 0.35%. On the other hand, when we used sequential deposition, a higher efficiency up to 1.12% was obtained using P3HT as the HTL. We confirmed that the low efficiency of MASnBr3 based perovskite solar cells is due to their relatively high resistance and the fast formation of Sn–Br oxide on the top surface by air exposure during fabrication. The sequential deposition method helped avoid such oxidation resulting in higher efficiencies.

Halide perovskite is one of the most promising semiconducting materials in a variety of fields such as solar cells, photodetectors, and light-emitting diodes. Lead halide perovskite single crystals featuring long diffusion length, high carrier mobility, large light absorption coefficient and low defect density, have been attracting increasing attention. Fundamental study of the intrinsic nature keeps revealing the superior optoelectrical properties of perovskite single crystals over their polycrystalline thin film counterparts, but to date, the device performance lags behind. The best power conversion efficiency (PCE) of single crystal-based solar cells is 21.9%, falling behind that of polycrystalline thin film solar cells (25.2%). The oversized thickness, defective surfaces, and difficulties in depositing functional layers, hinder the application of halide perovskite single crystals in optoelectronic devices. Efforts have been made to synthesize large-area single crystalline thin films directly on conductive substrates and apply defect engineering approaches to improve the surface properties. This review starts from a comprehensive introduction of the optoelectrical properties of perovskite single crystals. Then, the synthesis methods for high-quality bulk crystals and single-crystalline thin films are introduced and compared, followed by a systematic review of their optoelectronic applications including solar cells, photodetectors, and X-ray detectors. The challenges and strategical approaches for high-performance applications are summarized at the end with a brief outlook on future work.

The exploration of new physical properties for various THz-based applications, such as THz-wave sensing, modulation, and imaging devices, is a key challenge in the research on organic–inorganic hybrid perovskite materials. These THz-based applications require satisfactory, sensitive, and stable absorption properties with values between 0.5 and 3 THz. To achieve these properties, candidate materials should possess a purified structure that induces regular and fixed phonon modes without any defects or impurities. CH3NH3PbBr3, an organic–inorganic hybrid perovskite thin film produced by a sequential vacuum evaporation method on a flexible PET substrate, was investigated in this study. Although the thin film contains only molecular defects related to CH3NH2 incorporated into the perovskite structure, our THz-wave absorption measurement and first-principles simulation confirmed that these molecular defects do not influence the three phonon modes originating from the transverse vibration (0.8 THz), the longitudinal optical vibrations (1.4 THz) of the Pb–Br–Pb bonds, and the optical Br vibration (2.0 THz). After spin-casting an ultrathin PTAA polymer protective layer (5 nm) on the hybrid perovskite thin film, it was additionally observed that there was no significant effect on the phonon modes. Thus, this novel flexible organic–inorganic hybrid perovskite material is a potential candidate for THz-based applications. A material useful for security imaging has been identified by an international team of scientists. Radiation between the infrared and microwave parts of the electromagnetic spectrum can pass through clothing. This so-called terahertz radiation is valuable for security screening technology as it can identify a wider range of materials than metal detectors and is much quicker than a manual pat-down. A team led by Young-Kyun Kwon from Kyung Hee University, Seoul, South Korea, and Min-Cherl Jung from the University of Tsukuba, Ibaraki, Japan, demonstrated that a material already used with great success in optoelectronic and solar cell applications, known as an organic–inorganic hybrid perovskite, also has useful terahertz properties. The team created thin films of this material on a flexible substrate and showed that it absorbed radiation at fixed terahertz frequencies. Phonon modes of CH3NH3PbBr3 hybrid perovskite thin film.

Understanding the defect structure in organic-inorganic hybrid perovskite material (OHP) is a crucial role to explain several physical properties such as material stability, energy band, carrier mobility, and so on. In the solar-cell applications using OHP, finding, understanding, and controlling defects is essential to making a more advanced device with high efficiency and stability. Naturally, we need to find, understand, and control the possible defects in OHP. However, the defect research field in OHP material is just beginning now. In this short review, we will explore the kinds of defects and their effects on OHP.

To understand the instability of Sn-based perovskite, CH

In the past few years, lead halide perovskite solar cell power conversion efficiencies have risen by using a wide variety of fabrication methods and just passed 20%. Perovskite solar cells are typically fabricated in a glovebox to strictly avoid any water exposure. A dry atmosphere significantly increases equipment and operational costs for industrial processes, so ambient perovskite fabrication will be less expensive and more attractive. In this work it is demonstrated that ambient annealing is comparable to annealing in dry N2. Perovskite films annealed in a standard dry N2 environment are compared with those annealed in ambient environment with 50% relative humidity. Solar cell devices were prepared with a planar structure configuration and annealed at one of three different temperatures (105, 115, or 125 °C) in either N2 or ambient air. For all temperatures, the average efficiencies for the devices annealed in air are higher than those annealed in dry N2. The highest efficiency achieved for air-anneal...

The molecular order of organic semiconductors at the gate dielectric is the most critical factor determining carrier mobility in thin film transistors since the conducting channel forms at the dielectric interface. Despite its fundamental importance, this semiconductor-insulator interface is not well understood, primarily because it is buried within the device. We fabricated dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) thin film transistors by thermal evaporation in vacuum onto substrates held at different temperatures and systematically correlated the extracted charge mobility to the crystal grain size and crystal orientation. As a result, we identify a molecular layer of flat-lying DNTT molecules at the semiconductor-insulator interface. It is likely that such a layer might form in other material systems as well, and could be one of the factors reducing charge transport. Controlling this interfacial flat-lying layer may raise the ultimate possible device performance for thin film devices.

© The Royal Society of Chemistry.2015. Poly(3,4-ethylenedioxythiophene)-poly(styrenesulphonate) (PEDOT:PSS) is the most used organic hole injecting or hole transporting material. The hole carrying matrix PEDOT is highly doped by the acidic dopant PSS. When coated onto a substrate, PEDOT:PSS makes a highly uniform conductive layer and a thin (

This work covered the application of thermally reduced graphene oxide (rGO) as a hole-transport layer (HTL) to enhance stability of normal P3HT:PCBM-based bulk-heterojunction solar device. This device showed approximately the same performance of device using PEDOT:PSS as HTL (3.14%). After 3 days, exposure of an unsealed device in 1 sun illumination, rGO device resulted in 67% degradation of performance, whereas samples fabricated with PEDOT:PSS or without HTL degraded to more than 88% in efficiency. By simulation into an equivalent circuit, impedance analysis demonstrated that this degradation was strongly depended on the buffer materials. The use of the thermally rGO as buffer material could reduce the change of resistance in both HTL and bulk layer as well as avoid the accumulation of space charges in the active film.

“Flextrodes” are flexible transparent electrodes consisting of ZnO(100 nm)/PEDOT:PSS/silver grid/polyethylene terephthalate (PET) fabricated using a roll-to-roll process. Flextrodes provide a zinc oxide surface on a high-conductivity electrode while maintaining reasonable transparency and good flexibility. They are optimized for use as cathodes (i.e. low work functions) in inverted organic solar cells (OSCs). As-received Flextrode samples have a surface contamination layer that insulates. Prior to use in OSCs, this contamination layer needs to be removed. We tested two surface cleaning methods, i.e., UV-ozone and oxygen plasma, with various treatment times. After cleaning samples were characterized in terms of water contact angle, UV–visible transmittance, and 4-point probe conductivity, using conductive atomic force microscopy, and X-ray/ultraviolet photoelectron spectroscopy. Based on these measurements, we identified optimal conditions and were able to recover work functions of 3.4–3.6 eV without damaging the Flextrodes.

We investigated the chemical states of In3Sb1Te2 (IST) thin film using high-resolution X-ray photoelectron spectroscopy (HRXPS) with the synchrotron radiation during in-situ annealing in ultra-high vacuum. To obtain the oxygen-free amorphous IST (a-IST), we performed the mild Ne+ ion sputtering. And also we confirmed the relative a-IST stoichiometry to be 54%:17%:29% based on HRXPS data. At the first and second phase transition temperatures of 350 and 400 °C, we observed the dramatic changes of chemical states from a-IST to InSb and the mixture of crystalline-IST and InTe, respectively. There was a depletion of Sb atoms on the surface after annealing at 750 °C. We assume that Sb atom is a key for the phase transition in IST. However, chemical state of the Sb in IST is unstable during the phase transition and it will be caused with the non-reversible process by this structural instability.

We fabricated C-doped (1.5 wt.%) In3Sb1Te2 (CIST) thin films with amorphous phase (a-CIST) using a sputter method. Two electrical-phase-changes at 250 and 275 °C were observed in the sheet resistance measurement. In order to understand the origin of these electrical-phase-changes, all samples were characterized by XRD, TEM, and HRXPS with synchrotron radiation. In a-CIST, only weak Sb-C bonding was observed. In the first electrical-phase-change at 250 °C, strong Sb-C bonding occurred without an accompanying structural/phase change (still amorphous). On the other hand, the second electrical-phase-change at 275 °C was due to the structural/phase change from amorphous to crystalline without a chemical state change.

We investigated chemical states of a Sb2Te3 thin film with the polycrystalline phase by using high-resolution x-ray photoelectron spectroscopy with synchrotron radiation. The Sb2Te3 thin film was formed by sputtering. The rhombohedral phase was confirmed by x-ray diffraction. To remove the surface oxide, we performed Ne+ ion sputtering for 1 hour with the beam energy of 1 kV and post-annealing at 100oC for 5 min in ultra-high vacuum. We obtained the Te and Sb 4d core-levels spectra with the peaks at the binding energies of 40.4 and 33.0 eV, respectively. The full-width of half maximum of both the Te and Sb 4d 5/2 core-levels is 0.9 eV. The Te and Sb core-levels only show a single chemical state, and we also confirmed the stoichiometry of approximately 2：3.

A series of hybrid heterocyle-containing electron-transport materials (ETMs) with different pyridine substitution positions in a single molecule were successfully synthesized by regioselective sequential palladium-catalyzed Suzuki cross-coupling reactions. B3LYP calculations show that the experimental regioselectivity is consistent with the trends in calculated bond dissociation energies of the carbon–halogen (C–X) bonds of the reactants and intermediates. The two carbon species associated with C–N and C–C can be detected by X-ray photoelectron spectroscopy. Extremely low turn-on voltages (Von) of 2.1 V for electroluminescence, which are readily 0.2–0.3 V lower than the minimum value of the emitted photon energy (hv)/e, were experimentally achieved by utilizing the developed ETMs as an electron-transport and hole/exciton-block layer for the classical fac-tris(2-phenylpyridine) iridium (Ir(PPy)3)-based green phosphorescent organic light-emitting devices (OLEDs). In addition, hitherto the lowest operating v...

Chemical states of N-doped GeTe (N: 8.4 at.%) thin film (NGT) in structural phase transition were investigated by near-edge x-ray absorption of fine structure and high-resolution x-ray photoelectron spectroscopy with synchrotron radiation. We found the NaCl-like structure in NGT by x-ray diffraction at around 300 °C. Preparatory to the analysis of chemical states, after mild Ne+ sputtering we obtained clean amorphous NGT, which showed the N2 vibration mode peak in the N K-edge absorption spectrum. After annealing, the N2 molecular peak disappeared completely and we assumed that nitrogen was contributed only to the Ge atom in structural phase transition by analyzing Ge 3d and Te 4d core-levels.

We fabricated and analyzed the chemical states of carbon-doped (5.2–13.2 at.%) Ge 2 Sb 2 Te 5 thin films on Si substrates using high-resolution, X-ray photoelectron spectroscopy with synchrotron radiation. Thin films were completely amorphous and their phase-change temperature was 150 °C higher than for un-doped GST. As the carbon doping concentration increased, new chemical states of Ge 3 d with 29.9 eV and C 1 s with 283.7 eV core-levels were observed. The doped carbon was bonded only with Ge in GST and doping was saturated at 8.7 at.%.

CH3NH3PbI3 thin films were formed with various deposition rates of PbI2 first layer using a sequential vacuum evaporation method (SVE) to understand the formation behavior. Under low PbI2 deposition rates with 1 and 3 A s−1, the thin films did not form the hybrid perovskite structure. Over the 6 A s−1 deposition rate, the perovskite structure is observed with the remaining PbI2 and an intermediate phase together. In the 10 A s−1, the intermediate phase is increased, and the CH3NH2 molecular defect is observed. The hybrid perovskite thin film formed by SVE is confirmed with tiny grains and CH3NH2-incorporated intermediate state.

The chemical states of Bi (6 at.%)-doped GeTe thin film (GBT) in structural phase transition were investigated by high-resolution X-ray photoelectron spectroscopy (HRXPS). Clean amorphous GBT was phase changed to the NaCl-type crystalline structure by in-situ annealing under ultrahigh vacuum, during which transition, the binding energy and shape of the Te 4 d core-level showed no changes, the Ge 3 d core-level showed a spin-orbit split-enhanced feature with negligible chemical shift, and the Bi 4 f core-level became narrower and shifted towards the higher binding energy side by 0.25 eV. We suggest that as the film phase changed to the meta-stable crystalline structure, the Ge and Bi atoms moved to more constrained sites in the electron configuration.

We studied Ge nanocrystals ( nc -Ge) formed by bombarding Ge(100) surface with N 2 + gas followed by rapid thermal annealing (RTA). After initial N 2 + implantation, near-edge x-ray absorption fine structure and x-ray photoelectron spectroscopy (XPS) data showed formation of molecule-like N 2 species and chemically metastable Ge nitrides (GeN x ). The RTA transformed these into hemispherical nc -Ge of 10–25 nm in the diameter as clearly seen in transmission electron microscope images. XPS confirmed that the surface of the nc -Ge was covered with Ge 3 N 4 layer and underlying layer is also mostly likely Ge 3 N 4 . This simple process of forming isolated nc -Ge with Ge 3 N 4 surrounding layer can be useful in non-volatile memory applications.

We investigated the chemical states of InTe thin film in the structural phase transition from the amorphous to the crystalline phase, using high-resolution X-ray photoelectron spectroscopy with synchrotron radiation. We confirmed the structural phase transition by transmission electron microscopy. Clean amorphous InTe ( a -InTe) free of oxygen impurity was obtained after Ne + ion sputtering at the ion beam energy of 1 kV for 1 h. Additionally, we obtained crystalline InTe ( c -InTe) from clean a -InTe by annealing at 250 °C in an ultra-high vacuum. During the transition to the crystalline phase, the binding energy of the Te 4 d core-level was unchanged, but the peak width was somewhat wider than in the amorphous phase. In the case of the In 4 d core-level, the chemical shift was 0.1 eV at the higher binding energy between the amorphous and crystalline phases. The valence band maximum was shifted at the higher binding energy of 0.34 eV. We assumed that the Te atom was almost fixed and that the In atoms moved in the tight binding energy state to the center of the 4-Te atoms.

The electronic structures of AgNi1-xCoxO2 (0 les x les 1) delafossite oxides have been investigated by employing photoemission spectroscopy (PES) and X-ray absorption spectroscopy (XAS) in the soft X-ray regime of synchrotron radiation. The Ag 3d core-level PES spectra shift toward the higher binding energy with increasing x, in agreement with the metallic nature for low values of x and the insulating nature for high values of x in AgNi1-xCoxO2 . Further, the Ag 3d core-level PES spectra become more asymmetric with decreasing x, which reflects the larger number of electron-hole pairs in the Ni-rich regime. Valence-band PES spectra reveal that the band width of the occupied Ni 3d states is broader than that of the Co 3d states, implying the larger Ni 3d-O 2p hybridization than the Co 3d-O 2p hybridization. The Co and Ni 2p XAS spectra show that Co ions are in the low-spin Co3+ states for all x, while Ni ions are in the Ni2+-Ni3+ mixed-valent states. The Ni3+ component increases with x.

The chemical states of GeTe thin film are investigated using high-resolution X-ray photoelectron spectroscopy (HRXPS) with synchrotron radiation, during amorphous to crystalline structural phase transition. As the temperature increases from 250 to 400 °C, we observe the rock-salt crystalline structure and phase with X-ray diffraction (XRD) and transmission electron microscopy (TEM). Spin-orbit splitting of the Ge 3d core-level spectrum clearly appears after annealing at 400 °C for 5 min. However, the binding energy of the Ge 3d 5/2 core-level peak of 29.8 eV does not change in the amorphous to crystalline structural phase transition. In the case of the Te 4d core-level, change in binding energy and peak shapes is also negligible. We assume that the Te atom is fixed at a site between the amorphous and crystalline phases. Although the structural environment of the Ge atoms changes during the structural phase transition, the chemical environment does not.

We fabricated perovskite solar cells using a triple-layer of n-type doped, intrinsic and p-type doped 2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) (n-i-p) as hole transport layer (HTL) by vacuum evaporation. The doping concentration for n-type doped spiro-OMeTAD was optimized to adjust the highest occupied molecular orbital of spiro-OMeTAD to match the valence band maximum of perovskite for efficient hole extraction while maintaining a high open circuit voltage. Time-dependent solar cell performance measurements revealed significantly improved air stability for perovskite solar cells with the n-i-p structured spiro-OMeTAD HTL showing sustained efficiencies even after 840 h of air exposure.

Using scanning electron microscopy (SEM) and high-resolution x-ray photoelectron spectroscopy with the synchrotron radiation we investigated Si-based micro-clusters embedded in TaSiN thin films having oxygen contamination. TaSiN thin films were deposited by co-sputtering on fixed or rotated substrates and with various power conditions of TaN and Si targets. Three types of embedded micro-clusters with the chemical states of pure Si, SiOx-capped Si, and SiO2-capped Si were observed and analyzed using SEM and Si 2p and Ta 4 f core-level spectra were derived. Their different resistivities are presumably due to the different chemical states and densities of Si-based micro-clusters. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.