Photoinduced charge carriers at surfaces and interfaces of poly [2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] with Au and GaAs (original) (raw)

Charge Mobility and Photovoltaic Behavior of MEH-PPV Films Prepared by Various Methods

2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006

Charge carrier mobility and photovoltaic parameters was studied in poly[2-methoxy-5-(2`-ethyl-hexyloxy)-1,4-phenylene vi-nylene] (MEH-PPV) based films prepared by different methods. Polymer films have been obtained by drop casting and new method of slow solvent elimination (SSE)..Transient currents demonstrate non-dispersive and dispersive behavior in SSE and drop-cast films, respectively. In SSE films, hole drift mobility increases from 2.2•10-6 to 7.0•10-6 cm 2 V-1 s-1 with the electric field increase from 4.2•10 4 to 2.9•10 5 V•cm-1. These values are greater than the corresponding ones in drop-cast films by a factor of 4-5. This behavior indicates the difference in the morphology of the MEH-PPV films obtained by different methods. Possible reasons of the observed mobility enhancement in the SSE films are discussed.

Electrical and optical properties of thin films based on poly [2-methoxy-5 (2′-ethyl hexyloxy)-1,4-phenylene vinylene] doped with acridine orange dye with possible photovoltaic applications

Solar Energy Materials and Solar Cells, 2007

Conjugated polymers have high potential for efficient production of low-cost flexible optoelectronics devices such as solar cells, photodiodes and light emitting diodes. In this paper, the interaction between poly [2-methoxy-5 (2 0-ethyl hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and acridine orange (AO) dye has been studied to examine the role of charge pair separation and photocurrent generation in organic photovoltaic films. The AO dye concentration has been optimized on the basis of absorption spectra and photoluminescence (PL) studies carried over the films particularly, for photovoltaic applications. For this purpose, MEH-PPV polymer was dissolved in n-butyl acetate and doped with different concentration of AO dye solution. The Current-Voltage characteristics of MEH-PPV films, prepared by spin-coating technique on ITO-coated glass substrate have been determined as a function of temperature. For the cathode contact, Al was deposited using RF sputtering technique so that the current is predominantly due to holes. The conductivity increases by two orders of magnitude as the AO dye concentration increases to 2.65 mol L À1. In optical properties, we have studied the UV-visible absorption spectra, PL spectra of undoped and doped MEH-PPV films. The absorption studies show that the addition of AO dye does not significantly change (reduce) the absorption, which indicates the suitability of photon absorption. The PL spectra were recorded for MEH-PPV films, which become narrow on increasing the AO dye concentration. The PL studies indicate that up to certain concentration of AO dye in MEH-PPV films, PL intensity decreases as compare to that for undoped MEH-PPV film. The combined effect of increase in conductivity by two orders, decrease in PL intensity and no significant change in absorption makes the material suitable for photovoltaic applications.

Photovoltaic and photoconductive properties of aluminum/poly(p-phenylene vinylene) interfaces

Synthetic Metals, 1994

Photoconductive and photovoltaic properties of AI/PPV/ITO sandwich devices were investigated by measuring steady-state photocurrents resulting from illumination through the Al electrode. A built-in potential (Vh~) was detected at the AI/PPV interface. The voltage dependence of the photocurrent in the vicinity of Vb~ was measured at 1 mW/cm 2 of incident illumination to give an open-circuit voltage and a short-circuit current of 1.2 V and 6 x 10-7 A/cm 2, respectively. The dependences of the short-circuit current on excitation wavelength and illumination intensity are presented and the C-V characteristics of the AI/PPV interface are analyzed. The quantum collection efficiency decreased from 5% to 1% as the intensity of illumination increased from 10-s to 1 mW/cm 2. The photovoltaic conversion power efficiency was about 0.07% for intensities approaching 1 mW/cm 2. The Vh~ value was accounted for by surface band-bending at the Al/PPV interface.

An investigation about thin films of poly[2-methoxy-5-(2′-ethyl-hexyloxy) phenylene vinylene] (MEH-PPV) prepared by Langmuir-Schaefer technique

Journal of Materials Science, 2000

The Langmuir monolayer behaviour of poly [(2-methoxy-5-(2 -ethyl-hexyloxy) phenylene vinylene] (MEH-PPV) conducting polymer was investigated at air-water interface at different subphases containing anions. A uniform deposition of MEH-PPV monolayers was shown by UV-visible, electrochemical techniques, where the influence of anions on redox properties was investigated by cyclic voltammetric surveying. The nature of anions revealed significant changes in redox properties of the MEH-PPV LS films. The photoelectrochemical response of MEH-PPV LS conducting polymer was also investigated at length. C

Effects from Gold Electrodes on the Electron-Phonon Coupling of Poly( p -phenylenevinylene) Films

Journal of the Brazilian Chemical Society, 2015

Interface effects between metal electrodes and organic films are crucial for the overall performance of organic electronics devices. We investigate effects from gold electrodes deposited on spin-coated films of poly(p-phenylene vinylene) (PPV). While a thin Au layer (16 nm) did not affect the absorption and emission spectra of PPV, a 64 nm thick Au layer induced blue shifts in both spectra owing to the reduction in the effective conjugation degree of PPV segments. Upon combining photoluminescence and Raman scattering spectroscopies, we noted that the Au clusters interact preferentially with the phenyl rings of the polymer chain, leading to shifts in the vibrational modes at 1100 and 555 cm-1 and a significant change in the electron-phonon coupling inferred from the Huang-Rhys parameters. These results are consistent with theoretical predictions in ab initio calculations, which imply that the final properties of polymeric devices may be tuned with adequate conditions for electrode deposition.

Photoelectron spectroscopy of poly(p-phenylene vinylene)

Synthetic Metals, 1989

The electronic strtlcture of neutral and electrochemically doped poly(pphenyiene vlnyi~) (~v) has been examined by wing m~ ~. ~ interpretation of the C(is) core level spectra has been assisted by theoretical MD studies on low molecular weight model ccmpounds. The valencelevel spectra of neutral polymer are discussed in conjunction with states derived from tight binding model of conjugated chain. TD~ signal detected frcm the topmost electronic states is reduced after doping and neither arsenic 4d orbitals nor fluorine 2s orbitals contribute detectable to the doped polymer valence band.

Towards optimization of device performance in conjugated polymer photovoltaics: Charge generation, transfer and transport in poly(p-phenylene-vinylene) polymer heterojunctions

Solar Energy Materials and Solar Cells, 2008

We fabricate photovoltaics comprised layers and blends of a hole-transporting derivative of poly(p-phenylene-vinylene) with a variety of electron-transporters: titanium dioxide, a cyano-substituted PPV, and a fullerene derivative (PCBM) to enhance device performance. Photovoltaic device characterization is combined with time-resolved and steady-state photoluminescence to understand the nature of the excited state and its effect upon device performance. We find that morphological differences, such as chain conformation or domain size, often overshadow the effect of charge transfer, so that device performance is not necessarily correlated with rapid decay times. Exciton generation is found to be a similarly important factor in most devices. These results provide insight into non-optimized device morphologies.

Preliminary photovoltaic response from a polymer containing p-vinylenephenylene amine backbone

Solar Energy Materials and Solar Cells, 2007

Optoelectronic properties from a novel polymer, poly(p-phenylene N-4-n-butylphenyl-N,N-bis-4-vinylenephenylamine) (PNB) have been investigated. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the material were estimated to be À5.18 and À2.75 eV, respectively, measured with cyclic voltammetry. A single-layer device structure was prepared by spin-coating PNB thin films from a solution on top of an indium-tin oxide (ITO) substrate while aluminum was used as a top electrode. Current density-voltage (J-V) characteristic was measured which showed a typical rectifying behavior. Photovoltaic from a single-layered device was observed under a white arc lamp illumination. This was improved via a double-layer structure comprising vacuum evaporated copper phthalocyanine (CuPc) or N,N 0 -ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C 13 ) as an additional layer. The open-circuit voltage, short-circuit current and hence the efficiency were improved in the double-layer devices. An ITO/PNB/PTCDI-C 13 /Al device was estimated to have external quantum efficiency (EQE) around 1% at 330 nm. In a comparison of optical absorption and photocurrent spectra, it was demonstrated that the excitons could be separated and further, generated carriers drifting to the opposite electrodes more efficiently in the double-layer cells.

Photoelectron spectroscopy study of the energy level alignment at polymer/electrode interfaces in light emitting devices

Current Applied Physics, 2001

We report on the valence orbital structure of poly(para-phenylenevinylene) (PPV)-like oligomers. We studied these molecules as isolated oligomers in the gas phase, as well as in thin films deposited on metal substrates. We use a simple model based on a previously reported Hamiltonian that accurately describes the development of the low lying electronic excitations as a function of the number of repeating units. In the study on the thin organic films we report on the energy level alignment at metal / organic and organic / organic interfaces, where the organic layer is either a PPV-like oligomer or C 60 . The results are important for understanding organic photovoltaic devices.