Xingzhong Yan

Cu 2 ZnSnS 4 polycrystalline thin films with large densely packed grains prepared by sol-gel method

Cu2ZnSnS4 (CZTS) was obtained from a sol-gel precursor which consists of copper chloride, zinc chloride, tin chloride, and thiourea. CZTS thin films were prepared by spin- coating the sol-gel precursor followed by annealing in a nitrogen atmosphere. The morphology, composition, and structure of the absorber layer were studied by scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction, and Raman scattering. The optical measure- ment shows the bandgap of these films is ∼1.51 eV, and the optical absorption coefficient is on the order of 10 4 cm −1 . CZTS solar cells with a structure of low-alkali glass/Mo/CZTS/CdS/i- ZnO/ZnO:Al/Al grid were tentatively fabricated. The best solar cell showed a short-circuit current density of 5.06 mA/cm 2 , an open-circuit voltage of 358 mV, a fill factor of 34.66%, and an efficiency of 0.63% under AM1.5 (100 mW/cm 2 ) illumination. These results demonstrate the CZTS thin films were successfully deposited by a cheap sol-gel technique. C 2011 Society of

Mixed (porphyrinato)(phthalocyaninato) rare-earth(III) double-decker complexes for broadband light harvesting organic solar cells

Solution-processed organic-inorganic hybrid bulk heterojunction solar cells with the capability of broadband solar photon harvesting over the ultraviolet-visible-near-infrared spectral range are developed. A series of mixed (porphyrinato)(phthalocyaninato) rare-earth double-decker complexes, [MIIIH(TClPP){Pc(α-OC4H9)8}] (1–7; M = Y, Sm, Eu, Tb, Dy, Ho, Lu; TClPP = meso-tetrakis(4-chlorophenyl)porphyrinate; Pc(α-OC4H9)8 = 1,4,8,11,15,18,22,25-octakis(1-butyloxy)phthalocyaninate) and [YIII(TClPP)(Pc)] (8, Pc = unsubstituted phthalocyaninate), along with a heteroleptic bis(phthalocyaninato) yttrium double-decker complex [YIIIH(Pc){Pc(α-OC4H9)8}] (9), are synthesized and utilized as broadband absorbers and electron donors (D), whereas N,N′-bis(1-ethylhexyl)-3,4:9,10-perylenebis(dicarbox-imide) (PDI) or [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) is adopted as primary electron acceptor (A1). For suppressing the fatal back charge transfer at D/A1 interface, the D:A1 blend is fabricated within an in situ formed cheap inorganic network of nanoporous TiOx, which can act as a secondary electron acceptor (A2). For characterization of these structures, steady state spectroscopy, fluorescence dynamics, atomic force microscopy, current–voltage characteristics, and photoelectrical properties of the active materials or devices are investigated. Solar cells utilizing PDI as the primary acceptor show higher values in open circuit voltage, fill factor, and power conversion efficiency over those cells using PCBM as the primary acceptor. With a cell area of 0.36 cm2, good efficiencies of up to 0.82% are achieved by the aforementioned double-decker complex:PDI:TiOx blends under 1-sun air mass 1.5 global illumination. These results conclude that double-decker bis(tetrapyrrole) complexes are promising photovoltaic materials with tunable absorption and photophysical properties.

Non-aggregated hyperbranched phthalocyanines: single molecular nanostructures for efficient semi-opaque photovoltaics

A series of single molecular nanostructured hyperbranched phthalocyanines, HBMPc-COOH (M = H2, AlCl, Co, Cu, Zn), have been synthesized, characterized, and systematically studied as efficient semi-opaque sensitizers of TiO2 by using ultraviolet-visible absorption, steady-state and femtosecond time-resolved fluorescence, cyclic voltammetry, current–voltage and photoelectric measurements. The inherent steric effect within these hyperbranched structures effectively suppresses the aggregation of phthalocyanine rings on TiO2 surface, providing a facile approach for improving the photovoltaic performance of phthalocyanine-based dye sensitized solar cells (DSSCs). A power conversion efficiency of 1.15% along with a high incident photon to current conversion efficiency of 66.7% at 670 nm is achieved from HBZnPc-COOH sensitized solar cells. These results are consistent with findings from the femtosecond time-resolved fluorescence study, which reveals an ultrafast and efficient multi-phasic interfacial electron injection from both the Soret and Q bands to the conduction band of TiO2. The changing of the metal centers dramatically affects the optical, photophysical, electrochemical, and photovoltaic properties of the hyperbranched phthalocyanines. Zinc has been found to be the best metal center in the whole series for the design of hyperbranched phthalocyanine-based dyes for DSSC applications.

Organic photovoltaic cells made from sandwich-type rare earth phthalocyaninato double and triple deckers

This work presents organic-inorganic hybrid solar cells, which possess the capability for broad band photon harvesting from an ultraviolet-visible to a near infrared range. These solar cells are bulk heterojunction devices, which have been fabricated by free base phthalocyanine and rare earth phthalocyaninato double or triple deckers (electron donors) with a perylenediimide derivative (electron acceptor). Two-type cell structures with or without nanostructured TiO2 layers have been presented. A characterization of the structures, steady state spectroscopy, fluorescence dynamics, and photoelectrical property of these cells and the active materials has been carried out. A cell structure of In2O3:SnO2∕TiO2-active material-TiO2∕Al has shown a significant improvement in conversion efficiency.

Linkage Dependence of Intramolecular Fluorescence Quenching Process in Porphyrin-Appended Mixed (Phthalocyaninato)(Porphyrinato) Yttrium(III) Double-Decker Complexes

Three novel mixed (phthalocyaninato)(porphyrinato) yttrium double-decker complexes appended with one metal-free porphyrin chromophore at the para, meta, and ortho position, respectively, of one meso-phenyl group of the porphyrin ligand in the double-decker unit through ester linkage, 3-5, have been designed, synthesized, and spectroscopically characterized. The photophysical properties of these three isomeric tetrapyrrole triads were comparatively investigated along with the model compounds metal-free tetrakis(4-butyl)porphyrin H(2)TBPP (1) and mixed [1,4,8,11,15,18,22,25-octakis(butyloxyl)phthalocyaninato][tetrakis(4-butyl)porphyrinato] yttrium double-decker complex HY[Pc(α-OC(4)H(9))(8)](TBPP) (2) by steady-state and transient spectroscopic methods. The fluorescence of the metal-free porphyrin moiety attached through ester linkage at the meta and ortho position of one meso-phenyl group of porphyrin ligand in the double-decker unit in triads 4 and 5 is effectively quenched by the double-decker unit, which takes place in several hundred femtoseconds. However, the fluorescence of the metal-free porphyrin moiety attached at the para position of one meso-phenyl group of porphyrin ligand in the double-decker unit in triad 3 is only partially quenched, clearly revealing the effect of the position of porphyrin-substituent on the photophysical properties of the triads. Furthermore, the molecular structures of 3-5 were simulated using density functional theory calculations. It was found that the relative orientation between the metal-free porphyrin moiety and the double-decker unit for compound 3 is crossed, while those for compounds 4 and 5 are open- and closed-shellfish-like, respectively, which is suggested to be responsible for their different intramolecular fluorescent quenching efficiency.

Characterization of intrinsic ZnO thin film deposited by sputtering and its effects on CuIn1−xGaxSe2 solar cells

Intrinsic ZnO (i-ZnO) thin films were deposited on glass substrates by radio-frequency magnetron sputtering for exploring the effects of the deposition conditions. These films were optically, electrically, and structurally characterized. Results showed that the properties of i-ZnO thin films changed with the changing of deposition conditions. These i-ZnO films were also integrated into CuIn 1- x Ga x Se 2 (CIGS) solar cells. It was found that the incorporation of an i-ZnO layer in CIGS solar cells led to a significant improvement of homogeneity and efficiency of CIGS solar cells. An increment of 1.71% was gained in the average cell efficiency through adjusting the deposition conditions of i-ZnO layers. Detailed analysis showed that there was no improvement in cell efficiency under the deposition conditions favorable for growing the i-ZnO films. These results indicate that there should be a balance among the optimized performance of each layer deposited for high quality multi-layer devices.

Enhanced Singlet Oxygen Generation from a Porphyrin–Rhodamine B Dyad by Two‐Photon Excitation through Resonance Energy Transfer

Mitochondrial‐targeting photosensitizers have been associated with effective photodynamic responses. However, most photosensitizers absorb light between 400 and 700 nm, where light penetration through tissues is limited. Two‐photon excitation is a rational approach to improve light penetration through tissues. In this report, the two‐photon photophysical properties of a porphyrin–rhodamine B conjugate (TPP‐Rh), previously demonstrated to target the mitochondria, were evaluated. The properties studied included: two‐photon absorption (TPA) cross sections (σ2); resonance energy transfer (RET) kinetics and dynamics; and singlet oxygen generation. The conjugation of Rh B to TPP‐OH approximately doubled the σ2 of TPP‐Rh at 800 nm (40 ± 4 GM) compared with the parent porphyrin, TPP‐OH (16 ± 4 GM). Furthermore, the rate of DPBF oxidation by singlet oxygen generated from TPP‐Rh was twice as fast compared with that from TPP‐OH (73 % versus 33% in 10 min) following two‐photon excitation at 800 nm. In addition, a significantly stronger luminescence signal was detected from TPP‐Rh, than from TPP‐OH at 1270 nm, following two‐photon excitation. This study indicates that conjugating photosensitizers to Rh B could provide greater TPA at the near‐infrared range in addition to preferential mitochondrial accumulation for improved photodynamic responses.

AlSb Compound Semiconductor as Absorber Layer in Thin Film Solar Cells

Since industrial revolution by the end of nineteenth century, the consumption of fossil fuels to drive the economy has grown exponentially causing three primary global problems: depletion of fossil fuels, environmental pollution, and climate change (Andreev and Grilikhes, 1997). The population has quadrupled and our energy demand went up by 16 times in the 20th century exhausting the fossil fuel supply at an alarming rate (Bartlett, 1986; Wesiz, 2004). By the end of 2035, about 739 quadrillion Btu of energy (1 Btu = 0.2930711 Whr) of energy would be required to sustain current lifestyle of 6.5 billion people worldwide (US energy information administration, 2010). The increasing oil and gas prices, gives us enough region to shift from burning fossil fuels to using clean, safe and environmentally friendly technologies to produce electricity from renewable energy sources such as solar, wind, geothermal, tidal waves etc (Kamat, 2007). Photovoltaic (PV) technologies, which convert solar energy directly into electricity, are playing an ever increasing role in electricity production worldwide. Solar radiation strikes the earth with 1.366 KWm-2 of solar irradiance, which amounts to about 120,000 TW of power (Kamat 2007). Total global energy needs could thus be met, if we cover 0.1% of the earth’s surface with solar cell module with an area 1 m2 producing 1KWh per day (Messenger and Ventre, 2004). There are several primary competing PV technologies, which includes: (a) crystalline (c-Si), (b) thin film (a-Si, CdTe, CIGS), (c) organic and (d) concentrators in the market. Conventional crystalline silicon solar cells, also called first generation solar cells, with efficiency in the range of 15 21 %, holds about 85 % of share of the PV market (Carabe and Gandia, 2004). The cost of the electricity generation estimates to about

Theoretical study of two-photon absorption properties and up-conversion efficiency of new symmetric organic π-conjugated molecules for photovoltaic devices

4/W which is much higher in comparison to

Enhanced photoluminescence and the self-assembled fibrillar nanostructure of 5-(cholesteryloxy)methyl-8-hydroxyquinoline lithium in a gel state

0.33/W for traditional fossil fuels (Noufi and Zweibel, 2006). The reason behind high cost of these solar cells is the use of high grade silicon and high vacuum technology for the production of solar cells. Second generation, thin film solar cells have the lowest per watt installation cost of about