Covalent dyads of porphyrin-fullerene and perylene-fullerene for organic photovoltaics: Spectroscopic and photocurrent studies

Supermolecular complexes of zinc porphyrin or perylenediimide as covalent dyads with fullerene (C₆₀) in chloroform and as Langmuir-Blodgett layers on an Au substrate were studied. In our studies we have used following spectroscopic methods: electronic absorption, fluorescence and electron spin resonance in solution. Also infrared absorption spectra in a KBr pellet and reflectance-absorption in Langmuir-Blodgett layers were monitored. Photocurrent generation in a photoelectrochemical cell was also studied. The redistribution of charge both upon porphyrin linkage to C₆₀ and when the systems are deposited on the Au substrate was shown. Photocurrent examinations show a great influence of the fullerene presence on photoresponse of the systems.     

Photoelectrochemical studies on acid-doped polyaniline as sensitizer for TiO2 nanoporous film

Acid-doped polyaniline (PAn) as sensitizer for TiO₂ nanoporous film was investigated using electrochemical and photoelectrochemical methods. The photocurrent generation of TiO₂ nanoporous film sensitized by PAn extends into visible and infrared regions, and a maximum value appears in the region of 600–700 nm. The mechanisms of sensitization have been discussed in this paper.     

Photocurrent multiplication at n-GaN electrodes in formic acid solutions

Photocurrent multiplication (‘photocurrent doubling’) effects were studied at n-GaN electrodes in 1 M H₂SO₄ solutions containing formic acid. The photocurrent multiplication factor f was measured as a function of different parameters. It was found that f increases with increasing formic acid concentration, reaching a limiting value at high concentrations. Surprisingly, this limiting value for f was found to depend upon the extent of photoanodic etching prior to performing the photocurrent multiplication measurements: it increased from about 1.05 for ‘new’ electrodes to a maximum of 1.3 for etched electrodes. This suggests that somehow, intrinsic surface states are involved in the photo-oxidation of formic acid, the concentration of which changes due to etching. Further, it appeared that n-GaN dissolves photoanodically in 1 M H₂SO₄ solutions containing formic acid, even at very high concentrations. A mechanism, accounting for all of the experimental findings was proposed.     

Electrical and photoelectrochemical characteristics of flexible CdS nanocomposite/conducting polymer heterojunction

The electrical properties of CdS-polyvinyl alcohol (CdS-PVA) nanocomposites have been investigated in details. The junction behavior of CdS-PVA and a conducting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) heterojunction have been studied. The current–voltage characteristics of the nanocomposite samples have also performed at different bending angles. The bending study has been carried out after deposition of CdS-PVA and CdS-PVA/PEDOT:PSS heterojunction films on indium tin oxide coated (ITO) flexible polyethylene terephthalate (PET) substrates. Spectral dependent photoconductive properties of the nanocomposite-polymer heterojunctions have been investigated. The electrochemical photosensing behaviors have been demonstrated using CdS-PVA nanocomposites and CdS-PVA/PEDOT:PSS heterojunction films as photoanodes.     

Influence of Ga content on defects in CuInxGa1 − xSe2 based solar cell absorbers investigated by sub gap modulated photocurrent and admittance spectroscopy

In this work, we investigate the influence of gallium content on the defects properties of co-evaporated CuIn_xGa_1 − xSe₂ by sub gap modulated photocurrent spectroscopy and admittance spectroscopy techniques. A series of CuIn_xGa_1 − xSe₂ based solar cells with different gallium content in the range from 0% to 33%, and with the same CdS buffer layer have been investigated. On one hand, photocurrent spectroscopy results show 2 types of defects named D1 and D2, and on the other hand, admittance spectroscopy results exhibit only one type of defect. I-V curves show that one of the two defects probed by photocurrent is responsible of the dominant recombination mechanisms next to the heterointerface, between the absorber and the buffer layers. Moreover, I-V curves under AM 1.5 conditions show that the cell with no probed D2 defect presents the best photovoltaic performances.     

InGaAs/GaAs量子点红外探测器

与量子阱红外探测器相比,量子点红外探测器具有不制作表面光栅就能在垂直入射红外光照射下工作以及工作温度更高等优势。然而,目前阻碍量子点红外探测器性能提高的技术瓶颈主要来自组装量子点较差的大小均匀性、较低的量子点密度以及垂直入射下子带跃迁吸收效率低等原因。利用分子束外延技术研究了如何从量子点材料生长和器件设计两方面来克服这些困难,并且制作了几种不同结构的InGaAs/GaAs量子点红外探测器。 在77 K时,这些器件在垂直入射条件下观察到了很强的光电流信号。     

Analysis of photocurrent in the i-layer of GaAs-based n–i–p solar cell

A numerical investigation of the intrinsic layer effect on the improvement of GaAs n–i–p solar cell performances is presented. Solution of Poisson's equation together with continuity equations for electrons and holes allows the determination of carrier's density, electric field and recombination profiles within the i-layer. The analysis examines the effect of i-layer thickness on the electric field, recombination rate and collection efficiency. It is found that increasing the i-layer thickness increases the absorption while it reduces the electric field and increases the recombination rate. The three competing parameters have to be monitored simultaneously so as to obtain an optimal thickness. To achieve this, the variation of the total photocurrent is used as indicator. The photocurrent shows a sharp increase in the domain of very thin i-layers (<0.5 μm) then a saturation is reached for thicker layers (>1 μm), the simulation is performed for thicknesses up to 2 μm.     

Photoexcited states in directly synthesized trans-polyacetylene films studied by photocurrent measurement

A trans-polyacetylene film was directly synthesized to reduce defects introduced during usual thermal isomerization treatment. A photocurrent excitation spectrum of this film showed very low efficiency around a reflection peak which was accompanied with phonon side bands. This strongly indicates that the lowest optically allowed state of trans-polyacetylene is a 1¹B^u exciton state like other conjugated polymers, such as polydiacetylenes. Misinterpretations of the experimental results under the SSH model, because of the use of a film of low quality, are pointed out and reinterpretations are made according to the present conclusion.     

Photovoltaic Properties of the Modified n-Si（111） Electrodes with Ethyl and Carboxyls

n-Si（111） surface tailed -C2H5, -C2H4COOH, -C2H2COOH were prepared by the reactions among Si-H to ethyl-Grignard, methyl acrylate and ethyl propionate, and the carboxyls were formed under the existence of trifluoroacetic acid. The composite n-Si（111） electrodes were obtained by depositing Pt nanodots and the photovoltaic characteristics for these electrodes were studied in I^-/I3^- redox electrolyte. The j-U （photo current density-potential） behaviors of photo-voltage and photocurrent densities to the electrodes under solar illumination varied regularly with groups of -C2H2COOH〉-C2H4COOH〉-H〉-C2H5. The photo-voltage and photocurrent density of the electrode tailed -C2 H2COOH were -0.641 V and 5.25 mA/cm^2, respectively, more negative than those of the non-conjugated modification.     

Effects of spacer-chain length on the photoelectrochemical responses of monolayer assemblies with ruthenium tris(2,2′-bipyridine) - viologen linked disulfides

Photochemical and photoelectrochemical properties of ruthenium tris(2,2′-bipyridine) (Ru²⁺)-viologen (V²⁺) linked disulfides [RuCnVC₆S]₂ (n (number of methylene groups)=3, 7) with different spacer-chain lengths and Ru²⁺ disulfides [RuC_mS]₂ (m=13, 17) were compared. The luminescence intensity in CH₃CN was in the order of [RuC₁₃S]₂≈[RuC₁₇S]₂>[RuC₇VC₆S]₂[RuC₃VC₆S]₂, implying efficient photoinduced electron-transfer between Ru²⁺ and V²⁺ moieties in the linked compounds. The monolayer assembly of the compound was fabricated on a gold surface. In the presence of triethanolamine, the anodic photocurrent was clearly observed from the RuC_nVC₆S/Au (n=3, 7) electrode (gold electrode modified with [RuCnVC₆S]₂), and its intensity was substantially larger for n=7 than for n=3. Photocurrent action spectra for the RuC_nVC₆S/Au (n=3, 7) electrodes were well correlated with the corresponding electronic absorption spectra in solution. The photocurrent from the RuC₇VC₆S/Au electrode was reduced more effectively by the coexistence of a water-soluble viologen as compared with the RuC₃VC₆S/Au electrode. The photocurrent from the RuC_mS/Au (m=13, 17) electrode was very small. The results suggest that the spacer-chain length between the Ru²⁺ and the V²⁺ moieties profoundly affects the Ru²⁺-sensitized photocurrent.