Development of high efficiency organic solar cells based on charge transfer complexes

課題番号：2176022

Energy band bending induced charge accumulation at fullerene/bathocuproine heterojunction interface

The electronic properties of fullerene (C60)/bathocuproine (BCP)/Ag heterostructures were studied as a function of the BCP layer thickness by photoemission spectroscopy. For the thin BCP layer, the energy levels are flat and gap states exist at the interface. In contrast, energy band bending occurs at the C60/BCP interface when the BCP layer is thick, resulting in a considerable barrier for electron transport and therefore causing charge accumulation in organic solar cells. The results reveal that a thin BCP layer gives a much more favorable energy level structure and conform that charge accumulation is responsible to the anomalous current-voltage (I-V) curve

Effects of Zirconium Doping Into a Monoclinic Scheelite BiVO4 Crystal on Its Structural, Photocatalytic, and Photoelectrochemical Properties

Effects of zirconium (Zr) doping into BiVO4 powder on its structural properties and photocatalytic activity for O2 evolution were examined. The formation of BiVO4 powder crystallized in a monoclinic scheelite structure (ms-BiVO4) was achieved when the sample was doped with a relatively small amount of Zr. The photocatalytic activity of Zr-doped ms-BiVO4 powder was much higher than that of non-doped ms-BiVO4. However, further doping caused a reduction of photocatalytic activity for O2 evolution due to the occurrence of structural alterations into tetragonal scheelite and tetragonal zircon structures. Similar effects of Zr doping were also observed for the photoelectrochemical (PEC) system based on BiVO4 thin films doped with various amounts of Zr. Thus, Zr doping was confirmed to be effective for improvements of photocatalytic and PEC functions of BiVO4 for water oxidation

Fullerene mixing effect on carrier formation in bulk-hetero organic solar cell

Organic solar cells (OSCs) with a bulk-heterojunction (BHJ) are promising energy conversion devices, because they are flexible and environmental-friendly, and can be fabricated by low-cost roll-to-roll process. Here, we systematically investigated the interrelations between photovoltaic properties and the domain morphology of the active layer in OSCs based on films of poly-(9,9-dioctylfluorene-co-bithiophene) (F8T2)/[6,6]-phenyl C71-butyric acid methyl ester (PC71BM) blend annealed at various temperatures (Tan). The scanning transmission X-ray microscopy (STXM) revealed that fullerene mixing (ΦFullerene) in the polymer matrix decreases with increase in Tan while the domain size (L) is nearly independent of Tan. The TEM-S mapping image suggests that the polymer matrix consist of polymer clusters of several nm and fullerene. We found that the charge formation efficiency (ΦCF), internal quantum efficiency (ΦIQ), and power conversion efficiency (PCE) are dominantly determined by ΦFullerene. We interpreted these observations in terms of the polymer clusters within the polymer matrix

Morphology of F8T2/PC71BM Blend Film as Investigated by Scanning Transmission X-ray Microscope (STXM)

Clarification of the morphology of bulk heterojunction (BHJ) is indispensable for true comprehension of the organic solar cells. Here, we performed scanning transmission X-ray microscopy (STXM) for a poly-(9,9-dioctylfluorene-co-bithiophene) (F8T2)/[6,6]-phenyl C71-butyric acid methyl ester (PC71BM) blend film annealed at various temperatures (Tan). We found that the fullerene concentration within the polymer-rich domain decreases with Tan while the domain size (∼230 nm) is essentially unchanged. We will discuss the interrelation between the film morphology and the photovoltaic performance

水の光電気化学的酸化分解に活性な BiVO4薄膜光電極への Zr 添加効果

Effects of zirconium (Zr) doping into BiVO4 electrode on its structural properties and photoelectrochemical (PEC) property for water oxidation were examined. The BiVO4 electrodes with different Zr contents were prepared via a spin-coating process. Structural analyses using XRD and Raman spectroscopy indicated that all the samples consisted of mixtures of monoclinic scheelite (ms-BiVO4) and tetragonal scheelite (ts-BiVO4) structures. The highest PEC property for water oxidation was achieved when the sample doped with a relatively small amount of Zr (i.e., 0.5% of Zr-doped BiVO4); further doping caused a reduction of PEC property, probably due to the enhancement of carrier recombination induced by such excess Zr components

変調フラックス蒸着法と放射光解析法を利用した不純物ドープ有機薄膜太陽電池開発

科学研究費助成事業 研究成果報告書：基盤研究(C)2013-2015課題番号 : 2539006

Individual identification of free hole and electron dynamics in CuIn[1-x]Ga[x]Se[2] thin films by simultaneous monitoring of two optical transitions

The photocarrier dynamics of CuIn[1−x]Ga[x]Se[2] (CIGS) thin films were studied using white-light transient absorption (TA) measurements, as an understanding of this behavior is essential for improving the performance of solar cells composed of CIGS thin films. A characteristic double-peak structure due to the splitting of the valance bands in the CIGS was observed in the TA spectra under near-band-gap resonant excitation. From a comparison of the TA decay dynamics monitored at these two peaks, it was found that the slow-decay components of the electron and hole relaxation are on the nanosecond timescale. This finding is clear evidence of the long lifetimes of free photocarriers in polycrystalline CIGS thin films

Slow intraband relaxation and localization of photogenerated carriers in CuIn{1−x}Ga{x}Se{2} thin films: Evidence for the existence of long-lived high-energy carriers

The dynamics of free carriers in polycrystalline CuIn{1−x}Ga{x}Se{2} (CIGS) thin films were studied using picosecond time-resolved photoluminescence (PL) and femtosecond transient-absorption (TA) measurements. The PL spectrum and the TA decay component due to the band-to-band recombination of free carriers were observed in the picosecond time region. From excitation-photon-energy-dependent TA measurements, we identified a slow intraband relaxation of free carriers in the CIGS thin films. Collectively, the combination of PL and TA experiments reveal a global feature of energy relaxation and recombination processes of free carriers in the femtosecond to nanosecond time regions