This PDF file contains the front matter associated with SPIE Proceedings Volume 6656, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

By introducing a titanium oxide (TiO_x) layer between the active layer and the aluminum cathode in polymer based electronic devices, we have demonstrated devices with excellent air stability and with enhanced performance. The TiO_x layer acts as a shielding and scavenging layer which prevents the intrusion of oxygen and humidity into the electronically active polymers, thereby improving the lifetime of unpackaged devices exposed to air by nearly two orders of magnitude. We have also fabricated polymer tandem solar cells with a power conversion efficiency of 6.5%, with each layer processed from solution. A transparent TiO_x layer is used to separate and connect the front cell and the back cell. The TiO_x layer serves as an electron transport and collecting layer for the first cell and as a stable foundation that enables the fabrication of the second cell to complete the tandem cell architecture. We use an inverted structure with the low band-gap polymer/fullerene composite as the charge separating layer in the front cell and the high band-gap polymer composite as the charge separating layer in the back cell.

Some items to increase photovoltaic performances of dye sensitized solar cells (DSC) are reported. Focus is put on the fabrication of the electron collection path and ionic path. In order to increase the surface coverage of TiO₂ nano-particles with dye molecules, the dye adsorption on TiO₂ layers was carried out under a pressurized CO₂ atmosphere (CO₂ process). The CO₂ process promoted the dye adsorption and shortened the dye adsorption time to 1/10 - 1/100. In addition, solar cells prepared by the CO₂ process had higher Voc and Jsc than those prepared by the conventional dipping process. The increase in the photovoltaic performance was explained by the large electron diffusion coefficient in TiO₂ layers and by longer electron life time in TiO₂ layers. Thermally stimulated current measurement (TSC) implied that the surface electron trap on the TiO₂ nano-particle was passivated by the sufficient dye adsorptions on the TiO₂ surfaces. In addition, it was found that the dye aggregation was prevented by the CO₂ process, which increased the photovoltaic performances. Hybrid dye sensitized solar cells having two-dye-layer-structures were fabricated by the CO₂ process for the first time in order to absorb the light having wide range of wavelength. In addition, three-dimensional W electrodes were fabricated on the thick TiO₂ layer in order to collect electrons in the TiO₂ layer effectively. Solid type DSCs are reported. High performance quasi-solid DSCs were fabricated by preparing ionic paths in the quasi-solid electrolyte layers. The ionic path was fabricated by the surface modification of the straight nano-pore walls in a porous Al₂O₃ membrane, where, I^-/I₃ ^- ion species were concentrated and were expected to diffuse by Grötthuss mechanism.

All screen printed Dye Sensitized Solar cell modules were fabricated and demonstrated excellent electrical performances thanks to a monolithic interconnection based on highly conductive carbon layers. Attained efficiency at 1000 W/m² is 6 % with a fill-factor of 0.7. This monolithic module is very elegant to manufacture since the layers, including nano- TiO₂ spacer, catalytic active layer, conductive carbon and sealing are all printed. Such a module only requires one transparent conductive substrate which allows substantial manufacturing cost reductions. Moreover, only one co-firing cycle is sufficient, thus lowering the required energy at production. In addition, a quick staining process enables in-line production techniques. Modules of 10 x 10 cm are now being built for sampling and performance testing.

We have synthesized a new series of Ru complexes having β-diketonate and terpyridine ((tctpy = 4,4',4''- tricarboxy-2,2':6',2''-terpyridine) ligands as efficient panchromatic photosensitizers. Then we fabricated dye-sensitized solar cells (DSCs) using these Ru dyes. It was observed that newly synthesized Ru dye, Ru(tctpy)(dfac)NCS (3) (dfac = 1,1-difluoroacetylacetone), as well as previously synthesized Ru dyes, Ru(tctpy)(acac)NCS (1)(acac = acetylacetone) and Ru(tctpy)(tfac)NCS (2) (tfac = 1,1,1,-trifluoroacetylacetone) could absorb light wider than that of Ru(tctpy)(NCS)₃ (Black dye), which was well known as one of the best panchromatic dyes. DSC using dye (1) showed a low solar energy conversion efficiency (η) because of a narrow energy gap (ΔG₁) between HOMO level of dye(1) and I^-/I₃^- redox energy level. On the other hand, DSC using dye (2) produced such a high photocurrent (Jsc) as 25.4mA/cm². However this cell could not show a high efficiency such as 10% because of a narrow energy gap (ΔG₂) between LOMO level of dye (2) and TiO₂ conduction band. Finally, DSC using newly synthesized dye (3) showed such a high efficiency as 10.2% because of its suitable HOMO-LUMO energy levels, having optimum energy gaps of ΔG₁ and ΔG₂.

We proposed a solid=state image sensor with multi=layered structure on the basis of the combination of a charge read-out circuit with photoelectric conversion layers, which behave in similar fashion to sensitizing dyes in color films. We developed an organic photoelectric conversion layer, which selectively absorbs green light and transmits blue and red lights. By overlaying this layer on a silicon substrate having silicon photodiodes and a read-out circuit, we successfully produced a two-color sensor. Significant reduction in the dark current in the photoelectric conversion layer owing to appropriate carrier-blocking layers made it possible to take pictures with low level of noise.

This paper aims to propose a 3D nanostructured organic-inorganic hybrid photovoltaic device based on the ZnO nanostructures/poly(3-hexylthiophene)(P3HT):TiO₂ nanorods hybrids by solution processes at low temperature. An array of ZnO nanorods with a larger size of ~50 nm in diameter and ~180 nm in length are grown to provide direct pathways for efficient charge collection. TiO₂ nanorods with a size of ~5 nm in diameter and ~20-30 nm in length are incorporated into polymer to facilitate charge separation and transport by providing increased interfacial area and more effective transport pathway. The device performance with the inclusion of TiO₂ nanorods exhibits a seven times increase in the short circuit current with respect to that without TiO₂ nanorods.

We observed very small electronic density of states in the band gap of pentacene thin films deposited on inert surfaces using ultraviolet photoelectron spectroscopy (UPS) with ultrahigh sensitivity. We found, furthermore, that a pentacene film with less density of gap states gives a splitting of the HOMO band in UPS spectra with energy separation of about 0.45 eV due to the band dispersion even for ultrathin polycrystalline films. The results indicate that the gap states do not originate from electronic interaction between pentacene and the substrate surface but from imperfect molecular orientation/packing structure. We confirmed that the Fermi level pinning in the pentacene films originates from the intrinsic gap states depending on their density and energy distribution. The Fermi level position as well as appearance of the band dispersion in pentacene thin films therefore depends sensitively on perfectness of the molecular packing structure in each crystal grain.

Sensitizer dyes capable of producing two triplet excited states from a singlet excited state produced by the absorption of a single photon would allow an increase of the efficiency of photovoltaic cells by up to a factor of 1.5, provided that each triplet injects an electron into a semiconductor such as TiO₂. Although singlet fission in certain crystals and polymers was reported long ago, little is known about its efficiency in dyes suitable for use as sensitizers of photoinduced charge separation on semiconductors surfaces. Biradicaloids and large alternant hydrocarbons are desirable parent structures likely to meet the requirement E(T₂), E(S₁) > 2E(T₁) for the excitation energies of the lowest excited singlet (S₁) and the two triplet (T₁, T₂) states. We report results for 1,3-diphenylisobenzofuran, a model compound of the biradicaloid type. Its energy levels satisfy the desired relation, and in solution it shows no triplet formation by intersystem crossing. In the neat solid state, it forms triplets efficiently, and indirect evidence suggests that this is due to singlet fission. This appears to be the first compound displaying SF by design. When two such chromophores were combined into dimers, triplet formation yields of up to 9% were observed in polar solvents, possibly due to singlet fission, but possibly due to intersystem crossing. The triplet formation occurs in two steps, via an intermediate assigned as an intramolecular charge-transfer state and responsible for most of the observed excitation loss.

Recently, we have demonstrated an open circuit voltage of 1.0V and a power conversion efficiency of 3.4% in thin film solar cells, utilizing a new acceptor-substituted oligothiophene with an optical gap of 1.77 eV as donor and C₆₀ as acceptor. Stimulated by this result, we systematically study the energy and electron transfer processes taking place at the oligothiophene:fullerene heterojunction along a homologous series of these oligothiophenes. The heterojunction is modified by tuning the HOMO level using different oligothiophene chain lengths, while the LUMO level is essentially fixed by the choice of the acceptor-type end-groups (dicyanovinyl) attached to the oligothiophene. We study electron transfer at the heterojunction to C₆₀ using photoinduced absorption. The observed transitions are unambiguously identified by TD-DFT calculations. With increasing the effective energy gap of the donor-acceptor pair, charge carrier dissociation following the photoinduced electron transfer is eventually replaced by recombination into the triplet state, which alters the photovoltaic operation conditions. Therefore, the optimum open-circuit voltage of a solar cell is a trade-off between an efficient charge separation at the interface and a maximized effective gap. We conclude that values between 1.0 and 1.1 V for the open-circuit voltage in our solar cell devices present an optimum, as higher voltages were only achieved with concomitant losses in charge separation efficiency.

The electrical and photoelectrical properties of oxygen doped films of nickel phthalocyanine photovoltaic cells have been studied using ohmic gold and blocking indium electrodes. DC conduction processes identified depend both on the polarity and on the electric field strength. Under forward bias (gold electrode positive), conductivity is ascribed to Schottky diode behaviour at lower fields and by space- charge-limited conductivity controlled by an exponential trap distribution at higher fields. Under reverse bias, the conduction process is interpreted in terms of an electrode-limited to a bulk limited transition. The photovoltaic parameters of the cells are evaluated from the current-voltage characteristics under illumination. Space charge concentrations and barrier heights are estimated from the capacitance-voltage measurements both in dark and under constant illumination. From the action spectra of the photocurrent it is concluded that the carrier generation process is wavelength independent.

Organic photovoltaics (PV) are constrained by a tradeoff between exciton diffusion and optical absorption. The short exciton diffusion length within organic semiconductors demands the use of extremely absorptive materials. Unfortunately, the excitonic character of most organic materials yields highly structured absorption spectra, with regions of strong and weak absorption. Here, we describe a device architecture that decouples light absorption and exciton diffusion in organic PV through the addition of a light absorbing 'antenna' layer external to the conventional charge generating layers. Radiation absorbed by the antenna is transferred into the thin charge generating layers via surface plasmon polaritons (SPP) in an interfacial thin silver contact and radiation into waveguide modes. SPPs are a particularly effective energy transfer mechanism as they propagate in the plane of the PV rather than parallel to the incident radiation, thereby providing a more efficient means of pumping thin charge generating structures. We exploit efficient SPP-mediated energy transfer by attaching a resonant cavity antenna to a conventional small-molecular weight organic PV. We find that the resonant cavity antenna boosts the performance of a phthalocyanine-based PV in the absorption gap between the phthalocyanine Q and Soret bands. Off resonance the antenna serves as a mirror, but near the resonant wavelength, the antenna absorption is significantly enhanced, and energy is fed back into the PV cell via SPP-mediated energy transfer. Thus, the resonant antenna may be employed to supplement the performance of the PV cell at resonance, with no degradation off-resonance.

Organic solar cells were fabricated by stacking aromatic amine and C₆₀ layers. The energy conversion efficiency of these solar cells was low because of poor photoabsorption by these layers and short diffusion length of excitons. However, the photocurrent density was increased by about 3 times by the application of heat treatment to the stacked organic layers at about 140 °C, and the maximum energy conversion efficiency reached 1.1% under AM 1.5, 100 mW/cm² simulated solar light. The effect of the heat treatment was attributed to the infiltration of the amorphous aromatic amine compound into grain boundaries of the microcrystalline C₆₀ layer. From observation by electron microscopy, the mixed form of these two compounds near the interface was found to be suited to solar cells because the C₆₀ and aromatic amine phases wedge each other in a direction normal to two electrodes.

Significant progress is being made in the photovoltaic energy conversion using organic semiconducting materials. One of the focuses of attention is the nanoscale morphology of the donor-acceptor mixture, to ensure efficient charge generation and loss-free charge transport at the same time. Using small molecule and polymer blend systems, recent efforts highlight the problems to ensure an optimized relationship between molecular structure, morphology and device properties. Here, we present two examples using a host/guest mixture approach for the controlled, sequential design of bilayer organic solar cell architectures that consist of a large interface area with connecting paths to the respective electrodes at the same time. In the first example, we employed polymer demixing during spin coating to produce a rough interface: surface directed spinodal decomposition leads to a 2-dimensional spinodal pattern with submicrometer features at the polymer-polymer interface. The second system consists of a solution of a blend of small molecules, where phase separation into a bilayer during spin coating is followed by dewetting. For both cases, the guest can be removed using a selective solvent after the phase separation process, and the rough host surface can be covered with a second active, semiconducting component. We explain the potential merits of the resulting interdigitated bilayer films, and explore to which extent polymer-polymer and surface interactions can be employed to create surface features in the nanometer range.

Methods for scalable output voltage and encapsulation of organic photovoltaic cells are addressed in this paper. To obtain scalable output voltages, integrated photovoltaic modules comprised of a bulk heterojunction of poly(3- hexylthiophene) (P3HT) and a soluble C₇₀ derivative, [6,6]-phenyl C₇₁ butyric acid methyl ester (PCBM-70), were fabricated. Power conversion efficiency of individual P3HT/PCBM-70 cells was estimated to be 4.1 % for AM1.5 G illumination. Modules of one to four cells connected in series produced open-circuit voltages V_OC that linearly depend on the number of cells N as V_OC = N × 0.621 V with a nearly constant short-circuit current of 1.4 ± 0.1 mA. Separately, shelf lifetimes of more than one year were achieved for pentacene/C₆₀ solar cells by encapsulation with a 200-nm-thick layer of Al₂O₃ deposited by atomic layer deposition (ALD). In addition, the ALD process improved the open-circuit voltage and power conversion efficiency of the solar cells by thermal annealing that occurs during the process.

Organic photovoltaic cell is fabricated with tetrabenzoporhyrin (BP) as a donor material. Tetrabenzoporhyrin is formed by thermal conversion of the soluble precursor that has four bicycle rings instead of benzo-rings. Upon heat treatment above 150°C, the precursor molecule is converted to semiconductive benzoporphyrin, which is insoluble against conventional organic solvents. Hetero junction OPV cell is made of benzoporhyrin/fullerene layers with power conversion efficiency of 2.2%. Taking advantage of insoluble character of BP, p-i-n heterojunction OPV is successfully fabricated from solution, with BP/BP:fullerene/fullerene layers. This solution-processed p-i-n device exhibited further improvement of power conversion efficiency, 3.0%.

We report NREL-certified efficiencies and initial lifetime data for organic photovoltaic (OPV) cells based on Plexcore PV photoactive layer and Plexcore HTL-OPV hole transport layer technology. Plexcore PV-F3, a photoactive layer OPV ink, was certified in a single-layer OPV cell at the National Renewable Energy Laboratory (NREL) at 5.4%, which represents the highest official mark for a single-layer organic solar cell. We have fabricated and measured P3HT:PCBM solar cells with a peak efficiency of 4.4% and typical efficiencies of 3 - 4% (internal, NREL-calibrated measurement) with P3HT manufactured at Plextronics by the Grignard Metathesis (GRIM) method. Outdoor and accelerated lifetime testing of these devices is reported. Both Plexcore PV-F3 and P3HT:PCBM-based OPV cells exhibit >750 hours of outdoor roof-top, non-accelerated lifetime with less than 8% loss in initial efficiency for both active layer systems when exposed continuously to the climate of Western Pennsylvania. These devices are continuously being tested to date. Accelerated testing using a high-intensity (1000W) metal-halide lamp affords shorter lifetimes; however, the true acceleration factor is still to be determined.

For the first time, insoluble poly(isothianaphthene-3,6-diyl) (PITN(3,6)) thin-film has been successfully deposited from 3,4-diethynylithiophene via chemical vapor deposition polymerization. PITN(3,6) with an optical band-gap of about 1.8 eV, is a conjugated polymer with its backbone constructed through phenyl rings. The low band-gap was expected from an idea that the quinoid state of the polymer could be stabilized by the thiophene ring fused into the phenyl ring. Electrochemical analysis further provided the highest occupied molecular orbital and the lowest unoccupied molecular orbital levels with values of 5.0 eV and 3.2 eV respectively. PITN(3,6) was also synthesized through more conventional liquid-solution based synthesis (Bergmann cyclization). The structural analysis showed there were undesirable side reactions during the process leaving terminal alkyne groups and five membered thiophene rings within PITN(3,6) thin-film while PITN(3,6) deposited by CVDP showed very clean structure. Finally, a bi-layer heterojunction between carbonized poly(p-phenylenevinylene) and PITN(3,6) was fabricated. Without optimization, an open circuit voltage of about 300 mV was measured. Ultimately, CVDP can realize multi-layer organic optoelectronic devices on any platform because of its low substrate temperature and highly conformal coating capability.

Two solution-processible linear organic conjugated molecules with an electron-deficient core and triphenylamine (TPA) end groups, TPA-DCM-TPA and TPA-th-TPA, were used as donor and acceptor materials respectively in fabricating all organic solar cells (OSCs) by spin-coating method. Both the LUMO and HOMO energy levels of TPA-th-TPA are lower than those of TPA-DCM-TPA, which makes TPA-th-TPA a suitable acceptor for the OSCs with TPA-DCM-TPA as donor. The all OSC based on the blend of TPA-DCM-TPA and TPA-th-TPA (1:1, w/w) with LiF/Al as cathode, showed the photo-sensitivity in a broad wavelength range from 380 nm to 700 nm, high open-circuit-voltage (V_oc) of 1.21 V, and a power conversion efficiency of 0.21% under the illumination of AM 1.5, 100 mW/cm². The high V_oc of the device is benefited from the higher LUMO energy level of the TPA-th-TPA acceptor in comparison with that of the traditional acceptor PCBM.

We report on dye sensitized solar cells with PEDOT-PSS coated directly on flexible polyester substrate as counter electrode. The behavior of such plastic counter electrode in the presence of I ^- /I₃ redox electrolyte has been investigated with X-ray photoelectron spectroscopy. We have found that some of iodine species are "trapped" within the PEDOT-PSS layer. The presence of I₃ ^- , I₂ and PEDOT charge transfer complexes with iodine species may block the surface of the electrode. Furthermore, the PEDOT may be further oxidized (p-doped) during cell operation, which in turn may cause over oxidation and loss of conductivity in the PEDOT-PSS film. The interactions between PEDOT and iodine species may be enlarged because of the partial loss of PSS protective counter ion. The result is a decrease of PEDOT-PSS catalytic activity for reduction of I₃ ^- to I ^- in the redox electrolyte and worse cell performance than in the case of DSSC with Pt counter electrode.

The electrical and photoelectrical properties of oxygen doped films of nickel phthalocyanine photovoltaic cells have been studied using ohmic gold and blocking indium electrodes. DC conduction processes identified depend both on the polarity and on the electric field strength. Under forward bias (gold electrode positive), conductivity is ascribed to Schottky diode behaviour at lower fields and by space- charge-limited conductivity controlled by an exponential trap distribution at higher fields. Under reverse bias, the conduction process is interpreted in terms of an electrode-limited to a bulk limited transition. The photovoltaic parameters of the cells are evaluated from the current-voltage characteristics under illumination. Space charge concentrations and barrier heights are estimated from the capacitance-voltage measurements both in dark and under constant illumination. From the action spectra of the photocurrent it is concluded that the carrier generation process is wavelength independent.

Construction of efficient devices for light energy conversion, including photo-electronic and photovoltaic (PV) devices, is a big challenge for the current science and technology that will have important economic consequences. Most of the modern photovoltaic devices are based on silicon. An innovative approach to the construction of photovoltaic devices is the utilization of biological systems and principles designed for similar purposes by Nature. Biological electronic devices, proteins, have extremely high efficiency, precise spatial organization, and are inexpensive in fabrication. They can be fused with inorganic and organic materials such as conductors, semiconductors, conductive polymers, or quantum dots. The photosynthetic reaction center protein (RC) is one of the most advanced photo-electronic devices developed by Nature. It has nearly 100% quantum yield of primary charge separation, an extremely fast operation time (about 10^-9 s, or operation frequency of ~10⁹ Hz), and a very efficient stabilization of separated charges (ratio of charge separation rate to that of charge recombination is about 10⁴). The charge separation and stabilization takes place in a complex of 7 nm size and leads to the formation of a local electric field of about 10⁶ V/cm. A coupling of photosynthetic RC to inorganic electrodes is attractive for the identification of the mechanisms of inter-protein electron transfer (ET) and for the possible applications in the construction of protein-based innovative photoelectronic and photovoltaic devices. In this presentation we describe a new type of hybrid bio-inorganic photoelectronic devices based on photosynthetic proteins and inorganic materials. Using genetically engineered bacterial RCs and specifically synthesized organic linkers, we were able to construct self-assembled and aligned protein complexes with various metals and semiconductors, including gold, indium tin oxide (ITO), nanoporous TiO₂, highly ordered pyrolytic graphite (HOPG) and carbon nanotube (CNT) arrays. Our results show that photosynthetic protein-inorganic complexes can operate as highly efficient photo- and chemo-sensors, optical switches, photorectifieres, or photovoltaic devices.

It has been shown that dye sensitized solar cells (DSSCs) based on porous titanium dioxide (titania) layers have efficiencies exceeding 10%. Although porous structure has the advantage of large surface area for light harvesting, electron transport through the random nanoparticle network forming a porous film results in electron mobilities which are two orders of magnitude lower compared to the single crystal materials. Therefore, considerable efforts have been made to fabricate DSSC based on one dimensional nanostructures, such as nanowires or nanotubes. Titania nanotube arrays are typically made by anodization of titanium, followed by annealing to improve crystallinity. In this work, we investigated the influence of annealing temperature and annealing atmosphere on the crystal structure, the electron transport, and the solar cell performance of titania nanotube arrays. The titania nanotube arrays were prepared from electrochemically anodized titanium foils and their morphology and crystal structure were characterized by scanning electron microscopy and transmission electron microscopy. The crystal phases and the compositions of nanotube arrays were further investigated by X-ray diffraction for different annealing temperatures and X-ray photoelectron spectroscopy for different annealing atmospheres. For optimal annealing conditions, the short circuit current density of 4.27 mA/cm² and power conversion efficiency of 1.30% could be achieved under AM 1.5 simulated solar irradiation for 2 μm long nanotubes.

Normally, it has been widely acceptable that dye sensitized solar cell (DSSC) plays important roles compared to the conventional solar cells such as monocrystalline, polycrystalline, and even amorphous silicon in accordance with its low manufacturing and fabrication cost. However, the DSSC consists of many interfaces between anode and cathode such as semiconductor to dye and dye to electrolyte and electrolyte to platinum catalyst at the cathode. Therefore, the effect of charge recombination at dye-electrolyte interface is a major role to cell efficiency. One of major implementations to alleviate the recombination effect could be efficiently solved by adding hydrophobic co-adsorbent to dye solution. The co-absorbent molecule will be anchored to titanium dioxide semiconductor like dye and can be the barrier to protect the interface of the triiodide, dye and mesoporous titanium dioxide (TiO₂). In our works, we investigate on various hydrophobic co-adsorbent such as 1-adamantane acetic acid, cholic acid and chenodeoxy cholic acid. The amounts of the co-absorbent were varied as well as the amount of dye N719. It was found that the cholic and chenodeoxy cholic acid increase photovoltage and photocurrent, especially when the concentration was increased. This may be due to shift of conduction band (CB) to negative direction by the co-absorbent but 1-adamantane-acetic acid could not resist charge recombination. In addition multilayer of titanium dioxide was also studied on the effect of conversion efficiency. The maximum 4 layers of TiO₂ provided the best cell performance of 8.3 efficiency with the presence of cholic acid.

Control of morphology is a key issue in order to improve the performance of organic bulk heterojunction solar cells. Solar cells consisting of a blend of regioregular P3HT (poly(3-hexylthiophene)) and PCBM ([6-6]-phenyl C₆₁ butyric acid methyl ester) have demonstrated the highest efficiencies until now (up to 5 %). This performance was achieved by applying a post-production annealing, which is considered to induce a dual crystallization behavior. In order to control and tune the morphology, the phase behavior needs to be described in terms of the underlying fundamental thermodynamics. Hence, it is essential to obtain a phase diagram of the blend. In this study, the state diagram of P3HT:PCBM blends is measured by means of standard and modulated temperature differential scanning calorimetry (DSC). For the first time, the glass transition (T_g) of PCBM could be determined. All blends evidenced a single T_g, indicating an homogeneous blend is formed. Phase separation is thus only induced from crystallization and no "intrinsic" phase separation is occurring in the blend.

Organic photovoltaics are the focus of intense research efforts due to the low-cost of processing and their potential applications in flexible electronics. We herein report efficient, thick (2,500 Å) photovoltaic devices based on ternary mixtures of polycarbonate linked TPD (N,N,N',N'-tetrakis(phenyl) benzidine)) polymer (PTPD), small molecular weight radical salt of a TPD derivative and C₆₀ in an ITO/blend/Al configurations. While the addition of electron acceptor C₆₀ moiety to PTPD produces a 3 orders more, short circuit current (I_sc) of 0.22 mA/cm², the presence of salt increased it further to 0.33 mA/cm². This is attributed to the increased hole conductivity and absorption of PTPD matrix due to the presence of salt. In these 'PTPD/salt/C₆₀' ternary blend devices, the fill factors as well as the power conversion efficiencies increased with increasing salt concentration with the highest fill factor of 0.4 and power conversion efficiency of 0.47% obtained in 10% salt doped ternary ITO/PTPD-salt-C₆₀/Al device. To the best of our knowledge this is the first time that a radical salt has been used into an organic photovoltaic device configuration. Along with discussing these results, we would also be discussing the interplay of the three components of this ternary system to both open circuit voltage (V_oc) and I_sc. Further optimization in structure and morphology of these devices can lead to significant performance enhancement.

Alternative electrolytes for application in dye-sensitized TiO₂ solar cells were investigated. The electrolytes were prepared with NaI and I₂ as redox couple in a matrix consisting of poly(ethylene oxide-co-diethyleneglycolglicidyl methylether) and/or the ionic liquid N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide. Cyclic Voltammetry and Electrochemical Impedance Spectroscopy revealed that, increasing the relative amount of ionic liquid in the electrolytes, the impedance decreased and the ionic conductivity and the reversibility for the redox pair increased. For solar cells assembled with the polymer electrolytes, the efficiency for energy conversion decreased with light intensity, ranging from 3.2 to 1.4 % under 10 to 100 mW cm^-2. Using the ionic liquid electrolyte, the efficiency was ca. 1.8 %, independent of irradiation. For hybrid electrolytes, the best performance, considering mechanical stability and electrochemical properties, was achieved for an electrolyte consisting of 2:1 relative amount of polymer and ionic liquid. Solar cells assembled with this hybrid electrolyte presented, under 100 mW cm^-2, short-circuit current of 4.1 mA cm^-2 and 1.4 % for overall efficiency (ca. 3.0 % under 10 mW cm^-2).

A comparison study between a block copolymer and blend samples (D/A; donor/acceptor) revealed that their optoelectronic properties change significantly in different morphologies due to different processing conditions. The study shows that the photovoltaic performance of a block copolymer is better than that of corresponding donor/acceptor simple blend devices due to smaller scale (5-10 nanometers) donor/acceptor phase separation in the block copolymer, and that thermal annealing generally improves OE property due to potential better molecular packing.

We investigated the ability of silver thin metal films to enhance photovoltaic conversion efficiency in blends of poly-3-hexylthiophene (P3HT) and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM). By varying the thickness of the silver films and developing a new fabrication routine that involves annealing for long periods of time at low temperatures, we were able to reproducibly enhance photoconversion in P3HT/PCBM devices. Photovoltaic conversion efficiency was monitored using internal photon to current conversion efficiency (IPCE) and current-voltage measurements. We observed that plasmonic materials were able to enhance the conversion efficiencies of organic, bulk heterojunction devices. The relationship between the surface plasmon resonance wavelength and overall device performance is also presented with IPCE data. These preliminary studies indicate that plasmonic enhancement in bulk heterojunction devices show promise to improve the viability of organic solar cells.

In this paper, we described an engineered enhancement of optical absorption in an organic photovoltaic cell via the excitation of surface plasmon resonance (SPR) in spherical Au nanoparticles deposited on a device surface. We deposited gold nanoparticles with 5 nm in diameter on ITO (indium tin oxide) glass substrates and then coated poly (styrenesulfonate) / poly (2,3-dihydro-thieno-1,4-dioxin) (PEDOT) which can reduce the work function of metal atoms and poly {2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene} (MEHPPV) with Fullerene(C₆₀) mixtures that work as p-type and n-type organic semiconductors, respectively. By using Mie theory simulation, we could predict SPR resonance peak of gold nanoparticles and we assume the enhancement in electromagnetic field absorption within a device results in increased photocurrent response in organic p-n junction diodes with gold nanoparticles. Compared with the same organic photovoltaic structures without gold nanoparticles, the proposed device shows about 40 % power efficiency improvement under halogen illumination. Experimental results agree well to the prediction of simulation, which showed SPR can be applied to enhance optical absorption of organic materials.