For the first time, large area nanocrystalline titanium oxide based Dye Solar Cell modules with a size up to 45 x 45 cm have been manufactured with industrial methods and materials, opening a way to real products for selected markets. The electrical performances are measured, efficiency and stability are addressed, as well as the economic data showing an excellent cost of production of ca. 2 US $ per Wp for a one MWp production volume. The required steps leading towards end-user products and the challenges to overcome are also addressed.

Control of charge interfacial charge transfer is central to the design of photovoltaic devices. We report herein the application of insulating metal oxide blocking layers to control the charge recombination kinetics at a solid-state dye sensitised nanocrystalline inorganic/organic semiconductor interface. We show that the conformal growth of a ~1 nm thick overlayer of Al₂O₃ on a preformed nanocrystalline TiO₂ film results in a ~3-fold retardation in the rate of charge recombination at such an interface. This observation shows a good correlation with the current/voltage characteristics of dye sensitized nanocrystalline solar cells fabricated from such films, with the Al₂O₃ coating resulting in a 40% improvement in overall device efficiency

Quasi-solid dye sensitized solar cells (Q-DSSC) were fabricated by employing gel electrolytes containing ionic liquids and gelators. Sufficient physical contacts between nano-crystalline TiO₂ particles and gel electrolytes in nano-porous TiO₂ layers were achieved by solidifying gel electrolyte precursors after the cells are filled with the electrolytes. Photo-currents increased largely by embedding carboxylic acids among dye molecules on TiO₂ crystals. The nano-porous TiO₂ electrolytes were fabricated by dipping the dye anchored TiO₂ substrates in dilute solutions of carboxylic acids. It was found that resistances in the TiO₂ layers decreased by these treatments.

In dye-sensitized solar cells, electron transport in nano-porous thin TiO₂ film electrodes plays an important role in energy conversion efficiency. Previous studies have revealed that the electron transport property is largely influenced by electron density in the electrodes and the preparation methods of the TiO₂ electrodes. In this paper, we study the electron diffusion in nano-porous TiO₂ electrodes with and without dye adsorption. The electron diffusion coefficient is derived from pulsed laser induced current transients in the presence and absence of bias light. Measurements are repeated with various light intensities to examine electron density dependence. The experiments are performed for the electrodes prepared from two different TiO₂ particles and for two different electrolytes. For all cases, dye adsorption is found to increase electron diffusion coefficients under the same electron density in the electrodes. The increase of diffusion coefficients is confirmed by open-circuit voltage transient measurements. The charge trap on the electrode surface is studied from the relationship between open-circuit voltage and charge density in the dyed TiO₂electrodes. The reduction of surface charge trap density due to the dye adsorption is discussed.

Nanocomposite titanium dioxide/polymer photovoltaic cells have been fabricated using poly[2-(2-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEHPPV). Two different types of titanium dioxide were used, one synthesized using a sol-gel method, the other was a commercial paste. The crystal structure, porosity and absorption spectra of the titanium dioxide layers were measured, and the titanium dioxide synthesized using the sol-gel method had a much lower level of anatase. The photovoltaic properties of the ITO/TiO₂/MEHPPV/Au cells, which were similar for both types of TiO₂, were measured as a function of illumination power and compared with equivalent circuit models. A simple equivalent circuit model incorporating a diode, two resistances and a light induced current was inconsistent with the illumination -- dependent data and was improved by adding an illumination dependent shunt resistance. A very long lived, photo-induced increase in dark current was observed, which could not be explained by a polymer degradation mechanism or an increase in temperature under illumination, but was more likely to be due to trapped charge.

The covalent linking of acceptor molecules to electron donating conjugated polymer is an approach for the development of new photoactive materials for the fabrication of organic photoelectric conversion devices. With this strategy we have designed a polyalkylthiophene copolymer series containing in the side chain anthraquinone molecules as electron acceptor. The peculiar features of the copolymers are the good processability and the ease in tailoring the content of acceptor moieties. Their potential use as photoactive materials is investigated in terms of the photoinduced charge transfer properties, studied by FTIR photoinduced absorption and Light Induced Electron Spin Resonance spectroscopies. The results indicate the photoinduced electron transfer from the polythiophene backbone to the anthraquinone substituents and its tunability by changing the content of acceptor molecules. The photovoltaic response of these polymers is also discussed.

We discuss a generalized model for a solar cell, and the realization with heterogeneous photochemical photovoltaic converters such as the dye-sensitized solar cell. The different steps involved in the conversion of photon energy to electrical energy, indicate that a key point to consider is maintaining the separation of Fermi levels in the selective contacts to the absorber. In order to understand the irreversible processes limiting the efficient operation of the solar cell, it is necessary to obtain a precise description of the internal distribution of Fermi levels. We suggest the equivalent circuit as a central tool for obtaining such description, in relation with small perturbation measurement techniques. The fundamental steps of excitation and charge separation, and the losses by transport and charge transfer, can be represented by suitable circuit elements, and the overall circuit configuration indicates the operation of the selective contacts. The comparison of the equivalent circuits for heterogeneous dye solar cells and solid-state p-n junctions, shows the significant difference in the mechanisms of the selective contacts of these solar cells.

The concept of solid-state dye-sensitized TiO₂ solar cell in which the hole transport medium is an organic semiconductor is critically studied by examining the anode-TiO₂ interface and dye-hole conductor interface. The importance and the role of a compact hole-blocking TiO₂ layer in between the anode and the mesoporous layer is extensively studied by preparing this layer by spray pyrolysis using an automated procedure which guarantees reproducibility in obtaining constant thickness and quality of this crucial layer as seen in the current-voltage characteristics of the solar cells. To characterize the rectifying behavior of the blocking layer, cells with the structure, fluorinated tin oxide (FTO)/blocking TiO₂ layer/hole conductor/Au, were prepared and their current (I)-voltage (U) properties were investigated. Solid state solar cells were also prepared with different blocking layer thicknesses and their photovoltaic properties were investigated in order to study the influence of the blocking layer thickness on solar cell performance. In order to improve the dye-hole conductor interface, novel multifunctional molecules carrying dye units and triphenylamine moieties were synthesized and their influence as interface modifiers were studied. This interface modification results in doubling the external quantum efficiency of current conversion via improved charge transfer at the dye-hole conductor interface. Moreover, the recombination processes at this interface is drastically suppressed which leads to higher open circuit voltage and consequently higher power conversion efficiencies.

We report on the photovoltaic properties of solar cells containing a new discotic liquid crystalline material (DL-CuPc) based on copper phthalocyanine. In addition to being soluble, these materials can self-organize into highly ordered structures which can lead to good transport properties that can potentially be superior to those of amorphous materials. Increase in short-circuit current density and fill factor was obtained by thermal annealing of spin-coated DL-CuPc layer in bi-layer solar cells based on junction between DL-CuPc and C₆₀. These improvements are explained by change in structure and morphology upon thermal annealing.

Photovoltaic devices were fabricated using rhenium bis(arylimino)acenaphthene (DIAN) complex containing poly(p-phenylenevinylene). These polymers absorb strongly in the visible region at ca. 440-550 nm. In addition, this type of transition metal based polymers have been shown to exhibit large photo-sensitivity due to the presence of the rhenium complex, which has a relatively long-lived Metal-to-Ligand Charge Transfer (MLCT) character. By using this type of polymers, the metal content can be adjusted easily by simply changing the monomer feed ratio. Moreover, the excited state properties and electronic absorption properties can be modified by varying the structure of the diimine ligand coordinated to the metal. This approach allows us to fine-tune the absorption spectra of the polymers by employing different types of rhenium complex derivatives. PEDOT:PSS and PTCDI were used as the hole and electron transport layers, respectively. The ITO/PEDOT:PSS/DIAN-PPV/PTCDI/Al devices were found to exhibit photovoltaic response under the illumination of AM1 solar radiation. The short-circuit current I_sc, open-circuit voltage V_oc, and the fill factor FF were measured to be 38 μA/cm², 0.93 V and 0.21 respectively. Another photovoltaic device was prepared with the structure ITO/PEDOT:PSS/DIAN-PPV:TiO₂/PTCDI/Al and its photovoltaic properties were studied. The presence of TiO₂ will assist the electron transport of the DIAN-PPV to the PTCDI, in which the electrons can be collected at the aluminium electrode. The short-circuit current I_sc, open-circuit voltage V_oc, and the fill factor FF were measured to be 51 μA/cm², 1.18 V and 0.12 respectively. It was observed that the power conversion efficiency of photovoltaic devices related closely to the rhenium content and the structure of the rhenium complex used.

Few techniques are available where the morphology of blends can be determined in all three dimensions on a nanometer scale. Here we describe the use of a combination of techniques to resolve the morphology both laterally and vertically in spin cast films of a poly(p-phenylene vinylene)/methanofullerene blend. These blends are used as photoactive films in plastic bulk heterojunction solar cells where the performance strongly depends on the molecular morphology. In addition to depth profiling by dynamic time-of-flight secondary ion mass spectrometry (TOF-SIMS), tapping-mode atomic force microscopy (TM-AFM), transmission electron microscopy (TEM), absorption and emission spectroscopy and time-correlated single photon counting fluorescence measurements were used to investigate the morphology of ~100 nm thick spin cast composites with varying composition of 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM) and poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV). Combining all results showed clustering of PCBM into rather pure separate domains in a matrix of ~50 wt% MDMO-PPV for composites with PCBM concentrations 80-100 wt%, and no spontaneous stratification. Electrical characterization, under illumination and in the dark, of the composite devices revealed the percolation threshold for electron transport and showed a reduction in recombination-limitation for the photocurrent of these solar cells as a result of an improved charge transport and collection efficiency with increasing fullerene concentration.

We fabricated polymer-fullerene photovoltaic (PV) devices using various conjugated polymers, poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), poly{2-[4-(3,7-dimethyloctyloxy)-phenoxy]-1,4-phenylenevinyl-ene} (p-DMOP-PPV), and their copolymer system, p-DMOP-co-MEH-PPV. By comparing PV characteristics of such devices with a systematic change of the energy levels (ionization potential Ip and electron affinity E_a), we investigated the origin of open circuit voltage (V_oc) of the devices. Our results indicate that the magnitude of V_oc is governed by the difference between E_a of the fullerene and I_p of the polymer, which is not consistent with previous consideration of the work function difference between electrodes as in conventional metal-insulator-metal type devices.

Polymer bulk hetero junction solar cells were made from poly(2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene-vinylene) (MDMO-PPV) as donor and poly(cyanoetherphenylenevinylene) (PCNEPV) derivatives as acceptor material. In this paper we start out with discussing the synthesis of the materials. Subsequently, the main issues concerning the devices are treated. Annealing the devices yielded devices with encouraging efficiencies of 0.5% (1 sun, 100mW/cm²), as calculated from the maximum power points (MPP). AFM studies revealed that this anneal step improves especially the interface of the active layer with the under laying PEDOT:PSS, although mobility and morphology changes can not be ruled out. Lowering the molecular weight (Mw) of the MDMO-PPV gave a slight improvement of the device performance. Decreasing the Mw of the acceptor material, MDMO-PCNEPV (PCNEPV derivative with the same side chains as MDMO-PPV) and optimizing the layer thickness led to a device with an efficiency of 0.65%. Finally we looked into the influence of the nature of the side chains on the acceptor polymer. The results suggest that the closer the resemblance between donor and acceptor is the better the device performance.

In this report new PPV-PPE copolymers DE 69, DE 11 were compared with the state of the art materials MDMO-PPV and poly(3-alkylthiophenes) (P3DDT, P3OT). The optical band gap energy of the two copolymers DE 69, DE11 is somewhat higher than that one of MDMO-PPV. The electrochemical band gap was found to be lower for DE 69, DE11 related to for MDMO-PPV. The absorption coefficient of the new PPV-PPE copolymers is higher than for MDMO-PPV but in the same order of magnitude. Films from composites of MDMO-PPV/PCBM and DE69 or DE11 with PCBM show a clear photoluminescence quenching effect. At 77 K two kinds of LESR signals were identified, one of polarons (P^+.) and one of radical anions of fullerenes. The LESR results show strong differences in kinetics between the separation and recombination processes of photoexcited charge carriers. The relaxation rates of paramagnetic centers were estimated by microwave power saturation experiments. Photovoltaic devices were prepared under ambient conditions on flexible PET-ITO foils with MDMO-PPV/ PCBM (1:3 wt. %) with η_AM1.5 = 2.4% and DE 69/ PCBM (1:3 wt. %) with η_AM1.5 = 1.75% (A=0.25 cm², P_in = 100 mW/cm²).

The interface between polymer and fullerene in organic photovoltaic devices is improved by thermally induced interdiffusion. Starting from a bilayer of 2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene copolymer (MEH-PPV) and the Buckminsterfullerene (C₆₀) devices are heated in the vicinity of the glass transition temperature creating a gradient bulk-heterojunction. Interdiffused devices show photoluminescence quenching with concomitant improvements in photocurrents. Variation of the polymer layer thickness shows an increase in photocurrents with decreasing layer thickness within the examined thickness regime as transport of the separated charges out of the device is improved. The interdiffusion was observed in situ by monitoring the photocurrents during the heating step. Cross-sectional transmission electron microscopy reveals C₆₀ clusters of up to 30 nm in diameter in the interdiffused devices. The clustering of the fullerene molecules puts a significant constraint on the interdiffusion process.

Polymers of general constitutional structures: (formula available in paper) have been synthesized through the Horner- Wadsworth-Emmons olefination reactions of bisphosphonates 3 and fluorophoric dialdehydes 1, 2, 12 and 13 respectively. High molecular-weight, thermostable and transparent film-forming materials were obtained in high yields. The new compounds exhibit lyotropic and thermotropic liquid crystalline behavior. The insertion of triple bonds into the conjugated backbone enhances the electronaffinity relative to PPV and make them highly luminescent in solution as well as in solid state. Fluorescence quantum yields between 60 and 80% in solution and between 20 and 50% in film and extinction coefficients around 100,000 M^-1cm^-1 were obtained. In the cases of 4 and 5 are the solid state properties side - chains dependent. The three classes of polymers 5, 14 and 15 show similar photoluminescence behavior despite the differences in constitutional structures. This can be ascribed to identical chromophore system responsible for the emission. They are presently used in the design of light-emitting diodes and organic solar cells devices.

The aim of this work is to develop some new polymer materials with typical n-type semiconducting properties and low reduction peak potentials. Therefore new synthetic routes are presented leading to organo-soluble polyquinolines and polyquinoxalines. The results of the synthesis and characterization of the obtained new organo-soluble polymers are shown. The electrochemical reduction and oxidation behavior of these polymers is studied by cyclovoltammetric measurements. All studied polymers can be reversibly oxidized and reduced. In addition the absorption and luminescence properties are investigated. Polymer/polymer solar cells are prepared from blends of the new polyquinoxalines and poly-[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenvinylen] as active single layer. First results are discussed.

In this work, we investigate the influence of different indium tin oxide (ITO) surface treatments on the performance of organic solar cells with different device architectures. Two layer cells with different layer hierarchy (ITO/copper phthalocyanine (CuPc)/fullerene (C₆₀)/Al and ITO/C₆₀/CuPc/Cu) and three layer cells with mixed layer inserted between CuPc and C₆₀ were fabricated. We found that in all cases the short circuit current was the parameter which was most significantly affected by ITO surface treatment. However, the performance of the cells with C₆₀ layer in contact with ITO was markedly less sensitive to the ITO surface treatments compared to the cells with CuPc in contact with ITO. The cells with C₆₀ layer in contact with ITO also exhibited higher efficiency compared to the cells with CuPc in contact with ITO. We also fabricated two layer cells with structures ITO/CuPc/ perylene tetracarboxylic acid diimide (PTCDI)/Al and ITO/PTCDI/CuPc/Cu. In this case, we also obtain higher efficiency and lower sensitivity to ITO properties when “n type” material is in contact with ITO. The best obtained AM1 power conversion efficiency was 0.4% for ITO/PTCDI/CuPc/Cu cell and ITO/C₆₀/CuPc:C₆₀/CuPc/Cu cells.

A series of novel π-conjugated polymers containing ruthenium bipyridine complexes have been synthesized by a cross-coupling reaction and characterized. These polymers exhibit absorption maxima at around 330 - 350 nm (π-π*) and 460-500 nm (MLCT) respectively. They are soluble in common organic solvents and all polymers can be converted into transparent films. We investigated the influence of different donating and acceptor diethynylarenes on the UV/Vis spectra. The oxidation potentials, which have been measured by cyclic- and square-wave voltammetry, show a typical Ru^2+/3+ exhibiting at around + 1.26 V vs. SCE and an additional peak for triphenylamine containing polymers (+ 1.07 V C4c). The polymers were further characterized with photoluminescence measurements. When excited at 442 nm (C2), the polymer showed an emission peak at 690 nm. This peak is attributed to the MLCT states.

Multilayer photovoltaic devices were fabricated by the sequence adsorption of different polyelectrolytes. A ruthenium terpyridine complex containing poly(p-phenylenevinylene) was used as the polycation layer. This polymer has been shown to exhibit large photo-sensitivity due to the presence of the ruthenium complex, which has relatively long-lived excited state. This polymer absorbs strongly in the visible region at ca. 480 - 550 nm and it can act as the electron transporter. Sulfonated polyaniline was used as the hole-transporting polyanion layer. The ITO/(polyanion/polycation)_n/Al devices were found to exhibit photovoltaic properties under the illumination of AM1 solar radiation. The short-circuit current I_sc, open-circuit voltage V_oc, and the fill factor FF were measured to be 14 μA/cm², 0.84 V and 0.16 respectively. It was found that the power conversion efficiencies of the devices were dependent on the device thickness. This simple layer-by-layer self-assembly method allowed us to control the devices thickness accurately.

Photovoltaic effect has been studied on single- and multi-layer OLED devices based on phosphorescent PtOEP and Ir(ppy)₃ molecules, together with the electroluminescence (EL). The incident photon to current efficiency (IPCE) spectra of these PtOEP and Ir(ppy)₃ devices are similar to the absorption spectra of PtOEP and Ir(ppy)₃ molecules, respectively. This indicates that the photovoltaic effect is caused by the optical excitation of PtOEP and Ir(ppy)₃ molecules. The single-layer devices show weak EL luminance and low EL efficiency. Although the EL efficiency of the multi-layer Ir(ppy)₃ OLED device is high, the IPCE value is quite low, e.g. 0.013% in the single-layer device at the absorption peak wavelength of 386 nm. The same is true for PtOEP OLED, e.g. 0.0425% at the absorption peak wavelength of 371 nm. Such a low IPCE is considered to be due to low carrier mobility of PtOEP and Ir(ppy)₃ molecules. It was found that the multi-layer PtOEP and Ir(ppy)₃ OLED devices with emitting layer of guest-host system show much less efficient photovoltaic effect than the single-layer devices without guest-host.

We report the electropolymerization of poly(3-methylthiophene) (P3MT) in mesoporous titania. X-ray photoelectron spectroscopy (XPS) depth-profiling experiments confirm that the polymer filled the pores continuously from the bottom electrode to the top surface of the mesoporous titania. Photovoltaic cells with this structure show 0.23% power efficiency under 3.3mW/cm² 514 nm monochromatic illumination.

A novel tertiary nano structured photovoltaic device has been designed and preliminarily examined by recent development of target block copolymers. The unique feature of the device includes a -D(donor)-B(bridge)-A(acceptor)-B(bridge)- type of block copolymer primary structure, where D and A are conjugated donor and acceptor polymer blocks, and B is a non-conjugated and flexible chain, a π orbital stacked and conjugated chain self-assembled and ordered “secondary structure,” and a donor/acceptor asymmetric layers sandwiched D/A columnar “tertiary structure.” This device is expected to improve photovoltaic power conversion efficiency significantly in comparison to existing organic based donor/acceptor binary photovoltaic devices due to the reduction of “exciton loss,” the “carrier loss,” as well as the “photon loss” via three-dimensional space and energy level optimizations. Preliminary experimental results revealed better morphology and opto-electronic properties of -DBAB- vs. D/A blends.

Organic photovoltaic devices often show improved performances, if the active layer is made of a polymer blend. Due to the low miscibility of polymers the layer will phase separate and the lengthscale of the phase separation has a major influence on the device efficiency. We present a novel method to control the lengthscale of the phase separation, based on semiconducting polymer nanospheres (SPNs) forming the active layer. SPNs of M3EH-PPV (diameter 54nm) and CN-Ether-PPV (diameter 36nm) dispersed in water were produced by the miniemulsion process. Mono- and multilayers of these particles were fabricated by spincoating and photovoltaic devices utilizing these nanoparticles are shown to exhibit large external quantum efficiencies of up to 14%.

The spray deposition method has been developed as a new way of polymer ultra-thin film preparation for organic optoelectronic devices such as an organic photovoltaic cell (OPC). In this method, a highly diluted solution of an organic material is nebulized into air and concentrated under a controlled evaporation condition. The resulting aerosol is transported by a carrier gas and deposited onto a solid substrate. This method has substantial advantages that an almost insoluble and non-evaporative material can be fabricated into a thin film, and that a separate area coating and layer-by-layer structure of polymer materials can be performed. An OPC was prepared from highly diluted THF solutions (below 1 ppm) of fullerene/ poly-phenylenevinylene (PPV) derivative mixture. The device configuration, ITO/PEDOT-PSS/fullerene-PPV/LiF/Al, is known as a bulk hetero-junction PC. By control of temperature, we obtained homogeneous active layer by spray deposition. In addition, we can achieve power conversion efficiency of 0.63% using the active layer consist of fullerene: PPV(1:1). This method has significant potential to provide a structural control of the active layer and to reduce the cost of the OPCs drastically in spite that the power conversion efficiency is slightly lower than a PC prepared in same ratio by spin-coating.

Flexible plastic film-based electrodes for dye-sensitized solar cells were fabricated by low-temperature processes based on electrophoretic deposition techniques combined with post chemical necking treatments of TiO₂ layers. The film-type dye-sensitized photocell achieved solar conversion efficiency of more than 3%. A scheme for roll-to-roll manufacturing system based on the techniques is proposed.

We study the charge recombination kinetics and photovoltaic performance of composites of poly (9,9-dioctylfluorene-co-bithiophene) polymer with nanocrystalline TiO₂. Transient optical spectroscopy confirms that photoexcitation of the polymer leads to electron transfer to the TiO₂ and indicates that charge recombination is slow with a half-time of 100 μs to 10ms. Polymer penetration into thick porous TiO₂ layers is improved by melt-processing and treatment of the TiO₂ surface. We study the photovoltaic characteristics of devices with different layer thickness and interface morphology. Quantum efficiency (QE) of all devices is increased by reducing the TiO₂ and polymer layer thickness. Inserting a thin porous TiO₂ layer in to a thin bi-layer device increases the QE by a factor of five. The improved device shows peak QE and monochromatic power conversion efficiencies of over 11% and 1% at 440nm respectively. The device produced a short-circuit current density of 300μAcm^-2, a fill factor of 0.24 and an open-circuit voltage of 0.8V under AM1.5 illumination. The fill factor is increased from 0.24 to 0.40 by introducing an additional dip-coating layer and overall power conversion efficiency is increased by 50%. However, the device produced degraded current-voltage characteristics. We investigate this using an alternative polymers and different top contact metals.

Effects of a dead layer localized at the interface in a photodiode are studied theoretically. The model proposed here is developed for a Schottky junction but can be adapted to any other structure. A sharp decrease of the quantum efficiency in the short wavelength range is predicted, as generally observed experimentally. The various features encountered for the spectral responses are explained by the influence of the diffusion length L and of the dead layer thickness d. It is shown, moreover, that measuring the diffusion length from the photovoltaic short circuit spectra gives, in fact, the sum of L and d but determination of the maximum in the spectral response allows to separate the two.

Strategies towards flexible solid state solar cells based on nanocrystalline titanium oxide and organic hole conductor were investigated. For the flexible cell geometry a metal foil was used as substrate and a semi-transparent gold layer as counter electrode which allows light transmission (back illumination). The device performance of solid state cells based on SnO₂:F coated glass on the one hand and a metal foil on the other hand were characterized and compared by measuring the current voltage curves on back and front illumination.

We present a study of charge recombination in polyfluorene:[6,6]-Phenyl C₆₁-butyric acid methyl ester (PCBM) blend photovoltaic cells. The recombination kinetics of photogenerated charge carriers are investigated at room temperature by frequency and time domain photoinduced absorption. Monomolecular and bimolecular recombination processes are discussed in detail. Finally, a discussion on what kind of recombination can be dominant in our photovoltaic cells is addressed.

The work reported here explores the impact of polymer morphology on the physics and performance of perylene benzimidazole/poly(3-hexylthiophene) bilayer photovoltaic devices. By varying both the annealing temperature and the solvent used for polymer deposition, we demonstrate control of the polymer chain morphology. An increase in the relative ordering of the polymer chain conformation is observed through a shift in the absorption onset and absorption spectral shape, and results in improved photovoltaic performance.