Phthalocyanine/C₆₀ heterostructure organic solar cells were fabricated by evaporating highly purified materials under high vacuum conditions. 1%-2.5% external power conversion efficiencies were obtained with ITO / PEDOT:PSS / 300 angstrom ZnPc / 300 angstrom C₆₀ / 170 angstrom BCP/Al layering. The role of the buffer layers at the interfaces to the electrodes and their influence on the I-V characteristics was studied. Degradation of the organic cell caused by air and light exposure was investigated. Atmospheric oxygen diffusing into C₆₀ films was identified as external source of degradation. A second source was spotted in the interior of the cell.

Phthalocyanine (Pc) materials are commonly used in organic solar cells. Four different phthalocyanines, nickel phthalocyanine (NiPc), copper phthalocyanine (CuPc), iron phthalocyanine (FePc), and cobalt phthalocyanine (CoPc) have been investigated for organic solar cell applications. The devices consisted of indium tin oxide (ITO) coated lass substrate, Pc layer, and aluminum (al) electrode. It has been found that ITO/CuPc/Al Schottky cell exhibits the best performance. To investigate the influence of the active layer thickness on the cell performance, cells with several different thicknesses were fabricated and optimal value was found. Schottky cell exhibits optimal performance with one ohmic and one barrier contact. However, it is suspected that ITO/CuPc contact is not ohmic. Therefore, we have investigated various ITO surface treatments for improving the performance of CuPc based Schottky solar cell. We have found that cell on ITO treated with HCl and UV-ozone exhibits the best performance. AM1 power conversion efficiency can be improved by 30% compared to cell made with untreated ITO substrate. To improve power conversion efficiency, double or multiplayer structure are required, and it is expected that suitable ITO treatments for those devices will further improve their performance by improving the contact between ITO and phthalocyanine layer.

Current state-of-the-art bulk hetero-junction organic photovoltaic devices will be discussed based on poly(2-methoxy-5-(3',7'-dimethyl-octyloxy))-p-phenylene vinylene, (MDMO-PPV), as an electron donor and (6,6)-phenyl-C₆₁-butric-acid (PCBM)(a soluble C60 derivative) as electron acceptor. A brief review will be provided summarizing recent results on efficiency enhancement on morphological investigations. A significant increase in power conversion efficiency has been demonstrated for devices based on so-called 'sulphinyl' synthesized MDMO-PPV (η_AM1.5 = 2.9%) in comparison with devices based on 'Gilch' synthesized MDMO-PPV (η_AM1.5 = 2.5%). In order to understand the higher efficiency values obtained using a different solvent or a different MDMO-PPV-material, electrical and morphological investigations are being performed. Concerning the latter, it has been shown with various analytical techniques that the morphology of the blended photoactive films and also the power conversion efficiency of the corresponding photovoltaic devices are both simultaneously influenced by preparation conditions such as choice of the solvent and drying conditions.

Organic solar cells based on interpenetrating networks of conjugated polymer donors and fullerene-based acceptors with MA 1.5 efficiencies up to 3% were presented recently. For further improvement of the efficiency, the absorption of the solar light should be increased. This can be done by matching the active layer absorption better to the terrestrial solar emission spectrum and by increasing the absorption coefficient. In this contribution we present a combined spectroscopic and device study of novel materials that extend the absorption to the red. The systems studied are, among others, low bandgap polymers as electron donors or dye sensitized fullerene compounds. The photophysical properties are investigated by excited state spectroscopy and the materials are discussed with regard to their suitability for efficient photoinduced charge generation. The photovoltaic activity is demonstrated by photocurrent action spectra as well as by AM 1.5 efficiencies of prototype devices made using these novel materials.

We have explored the use of polymer / small molecule organic composites in the form of a polymer / perylene diimide heterojunction bilayer in order to combine the advantageous properties of both materials. Using the electron transporting perylene benzimidazole (PBI) and the hole conducting polymer poly[2,5-dimethoxy-1,4-phenylene-1,2-ethenylene-2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-1,2-ethenylene (M3EH-PPV), we have achieved increased power conversion efficiencies for a planar device of up to 0.71% under 80 mW/cm² white illumination. By varying the order of the photoactive layers, we have probed the mechanisms creating the photovoltage and found that the photovoltage is not determined by the difference in electrode work functions alone. In addition to the internal field, the interfacial chemical potential gradient, caused by exciton dissociation at the polymer / perylene diimide interface, appears to contribute to the photovoltage. We also discuss why, contrary to some expectations, the polymer / perylene diimide devices are more efficient than the analogous pure small molecule perylene diimide / phthalocyanine cells.

The microstructure of MDMO-PPV:PCBM blends as used in bulk hetero-junction organic solar cells was studied by Atomic Force Microscopy (AFM) and Kelvin Force Microscopy (KFM) to image the surface morphology and by means of Transmission Electron Microscopy (TEM) to reveal images of the film's interior. By introducing KFM, it was possible to demonstrate that phase separated domains have different local electrical properties than the surrounding matrix. Since blend morphology clearly influences global electrical properties and photovoltaic performance, an attempt to control the morphology by means of casting conditions was undertaken. By using AFM, it has been proven that not only the choice of solvent, but also drying conditions dramatically influence the blend structure. Therefore, the possibility of discovering the blend morphology by AFM, KFM and TEM makes them powerful tools for understanding today's organic photovoltaic performances and for screening new sets of materials.

Latest results show an 8.2 % efficiency obtained with industrially viable materials and processes. Stability in outdoors and simulated conditions are also presented. An elegant assembly technique has been developed for large area dye solar cells intended for outdoors applications. Solid-state dye solar cells show an efficiency up to 4 % in low light conditions, making them ready for indoor applications.

The photovoltaic performance of solid-state dye-sensitized solar cells based on spiro-MeOTAD (2,2'7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene) has been improved to 3.2% overall conversion efficiency under air mass AM 1.5 illumination by performing the dye adsorption in the presence of silver ions in the dye solution. Different spectroscopic methods, such as X-ray photoelectron, Fourier-transform infrared and UV-visible spectroscopy have been employed to scrutinize the impact of the silver on the dye-sensitized device. From spectroscopic evidence it is inferred that the silver binds to the sensitizer mainly via the amphidentate thiocyanate, allowing the formation of ligand-bridged dye complexes. The enhancement in overall device efficiency is a result of increased open circuit potential and short circuit current. The increased open circuit voltage was explained by the blocking of the dark current as a result of a closer packed dye layer and/or the partial formation of a dye double layer upon silver coordination. The increased short circuit current corresponds to the higher amount of ruthenium dye units adsorbed to the TiO₂ surface.

The electrodeless flash-photolysis time-resolved microwave conductivity technique (FP-TRMC) has been used to study photo-induced interfacial charge separation in bilayers consisting of a smooth, 80 nm layer of anatase TiO₂ onto which is spin-coated a 60 nm layer of a tetraphenyl porphyrin derivative with either unsubstituted or para-carboxy-substituted phenyl moieties; "TPP" or "TPPC". No significant difference in sensitization efficiency was observed between TPP and TPPC; both gave a maximum charge separation efficiency per incident photon of ca 1% on irradiation in their Soret band (430 nm). The low efficiency indicates that interfacial charge transfer occurs mainly for excited states produced in the first adsorbed monolayer of the sensitizer. Contrary to previous suggestions, specific interactions between the carboxy groups of TPPC and the TiO₂ surface do not appear to favor more efficient charge separation.

Using an aerosol technique, in which ultrasonically formed droplets of titanium tetraisopropoxide are pyrolysed, thin films of nanosized particles of anatase TiO₂ can be deposited. The size of the particles and the film morphology are strongly dependent on deposition parameters like reaction temperature, concentration of the precursor, and gas flow. At best, films can be formed consisting of homogeneous, stoichiometric anatase TiO₂ particles with a size of about 50 nanometer. With these films, solar cells have been constructed by spin casting poly(3-octyl)thiophene (P3OT) on top. Cell characteristics of the devices with a 1 μm film of TiO₂ and an equivalence of 30 nm of PT inside the pores are I_sc: 0.25 mA/cm², V_oc: 0.72 V, FF: 0.35 and η: 0.06% using white light with an intensity of 1000 W/m² (not AM 1.5). The IPCE is 2.5% at 488 nm.

Raman spectroscopy (RS) was used to study the interfacial species due to the presence of a redox couple in the electrolyte during the operation of dye-sensitized solar cells (DSSC). Two bands appear in the Raman spectra of polypyridinium (ppy) dyes adsorbed on nanocrystalline anatase. They can be directly connected to the presence of iodine/iodide couple because they are not present when hydroquinone/quinone (HQ/Q) redox couple is used. The band at 112 cm^-1 has already be assigned to the presence of tri-iodide; it disappears only at very high cathodic polarization. The band at 167 cm^-1 is due to the formation of an intermediate compound between the oxidized form of the dye , D⁺, and iodine; it involves a Py-I bonding. The use of different focusing proves that this compound is located below the adsorbed tri-iodide. Electrochemical Impedance Spectroscopy (EIS) allows to determine the charge transfer kinetics at the three main interfaces of the cell and to characterize the diffusion of tri-iodide species. Three different cell functioning regimes (photocurrent plateau, recombination, accumulation) were described. The Raman intensities of the two iodide-connected bands are investigated in each of the three regimes. The “Py-I” band is strong in the photocurrent plateau range and disappears in the recombination range.

Recently it has been discovered that some types of liquid crystals exhibit very fast electronic conduction characterized by high mobility over 10^-2 cm²/Vs, with is 1000 to 10000 times higher than that of the amorphous organic semiconductors practically used. Now, the liquid crystals are being recognized as a new class of organic semiconductors, that is, Self-organizing molecular semiconductors. The liquid crystalline materials enjoy crystal-like self-organizing molecular alignment and liquid-like fluidity. These unique nature provide us with a good basis for their application to the photo-voltaics in terms of quality photo-electrical properties and feasibility of large-area application. The general aspects related to photoconductivity in liquid crystalline materials, especially charge carrier generation and carrier transport properties are reviewed on the basis of our experimental results on the smectic liquid crystals and discuss their high potential as a new type of photo-voltaic materials.

Supra-molecular and nano-structured electro-active polymers are potentially useful for developing variety inexpensive and flexible shaped opto-electronic devices. In the case of organic photovoltaic materials or devices, for instance, photo induced electrons and holes need to be separated and transported in organic acceptor (A) and donor (D) phases respectively. In this paper, preliminary results of synthesis and characterizations of a coupled block copolymers containing a conjugated donor block (RO-PPV), a conjugated acceptor block (SF-PPV), and some of their electronic/optical properties are presented. While the donor block film has a strong PL emission at around 570 nm, and acceptor block film has a strong PL emission at around 590 nm, the PL emissions of final -D-B-A-B- block copolymer films were quenched by over 99%. Experimental results demonstrated an effective photo induced electron transfer and charge separation due to the interfaces of donor and acceptor blocks. The system is very promising for variety light harvesting applications, including “plastic” photovoltaic devices.

New dyes of the type Ru(II)(bdmpp)(bpy) [where bdmpp is 2,6-bis(3,5-dimethyl-N-pyrazoyl)pyridine and bpy is 2,2'-bipyridine-4,4'-dicarboxylic acid] are prepared and characterized by infra-red (IR), mass (MS) and electrospray mass spectroscopy (ES-MS) as well as ¹H NMR (1D and 2D) spectroscopies. The compounds present broad and very high intensity MLCT absorption bands in the visible and can be chemically anchored on TiO₂ films via ester-like linkage involving carboxylato groups. These complexes have been tested with success as potential molecular antennas in dye-sensitized solar cells. Both opaque and transparent nanocrystalline TiO₂ thin film electrodes obtained by a doctor blade technique sensitized by these complexes were incorporated in a sandwich type regenerative photoelectrochemical solar cell containing 0.1M LiI +0.01M I₂ in propylene carbonate as well as a platinized conductive glass counter electrode. The cell was characterized by Raman spectroscopy under anodic and cathodic bias. Two new vibration bands were observed in the lower frequency region. The first one at 112 cm^-1 is due to tri-iodide formed on the photoactive electrode, and the second one at 167 cm^-1 is a sign of the dye/iodide interaction and corresponds to a vibration in a chemically stable "DI" intermediate species. Under direct sunlight illumination (solar irradiance of 60 mW/cm²) by using a composite polymer solid state electrolye, the cell ITO/TiO₂/(Ru(II)(bdmpp)(bpy)(NCS))(PF6)/electrolyte/Pt-ITO produced a continuous photocurrent as high as 4.29mA/cm², and gave IPCE values about half of the corresponding values obtained by the standard N3 dye under the same conditions. The photovoltage is about 600 mV and the overall energy conversion cell’s efficiency is as high as 1.72%.

We have investigated the evolution of the growth front of perylene, an organic semiconductor with high carrier mobility, on glass and Au substrates grown side-by-side by vapor deposition. The films were grown with gradually increasing thickness which allowed us to examine both the spatial and temporal correlation of the surface roughness using atomic force microscopy. Our results show that perylene growth on glass and Au substrates is non-stationary. However, the instability during the growth is shown to depend largely on the substrate. A roughness exponent of 0.82 is obtained for glass and 0.84 for Au. A growth exponent of 0.21 is obtained for glass and 0.74 for Au. The results indicate the strong influence of the substrate on the film morphology and point to possible ways to control and improve it.