The most widespread expectations for the future role of organic solar cells are probably as an extremely low-cost, easily-replaceable, power-producing medium for a wide variety of portable applications. This picture has come about owing to the present-day relatively low efficiency and stability of organic solar cells compared to their far more mature inorganic counterparts. However, even with the highest-efficiency and most stable inorganic solar cells there are still serious questions as to whether such technology could ever be cost-competitive with fossil-fuelled power generation, except for special niche situations. We have recently proposed that very large parabolic dishes, if used to illuminate inorganic solar cells at solar intensities several hundred times larger than normal, could lead to fossil-competitive solar power generation. The paper will review the technical details and economic projections of such systems and will discuss the conditions under which it might be possible for them to employ organic solar cells.

Inorganic semiconductors are the backbone of present day photovoltaic (PV) technologies. The highest performance solar cells use III-V based materials in complex multijunction device structures and are used primarily in the space industry. The crystalline Si technologies are the mainstay of the commercial terrestrial markets and range from single crystal through large grain polycrystalline materials. Thin film PV technologies, which are approaching large scale manufacturing production levels, consist of polycrystalline CdTe, CuInSe2 and related alloys, and amorphous silicon (a-Si) and related alloys. The paper provides an historical background on the development of these inorganic PV technologies, followed by a discussion of the present status of each technology. The future directions being pursued to improve performance will also be discussed with emphasis on synergies between the technologies.

We have measured the electron and hole mobility in blends of poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-p-phenylene vinylene) (MDMO-PPV) and [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM) with varying MDMO-PPV/PCBM composition. It is shown that the electron mobility in the PCBM-rich phase gradually increases up to 80 wt.% PCBM, due to an increased number of percolated pathways from bottom to top electrode. In contrast to the expectations the hole mobility in the MDMO-PPV phase shows a similar behavior as a function of fullerene concentration; Starting at 40 wt.% with the value of pristine MDMO-PPV the hole mobility strongly increases and saturates beyond 67 wt.% at a value which is more than two order of magnitude higher. The large enhancement of the hole mobility and its saturation is related to recent findings on the film morphology of this material system.

Polymer blends allow control of microstructure in donor-acceptor photovoltaic devices. Here we present measurements of devices containing polyfluorene blend layers of different thicknesses, and we are able to extract characteristic transport lengths for electrons and holes. We also present analytical and numerical modeling of single-layer and bilayer photovoltaic devices, which demonstrates the importance of bound polaron pairs formed after the initial electron transfer from donor to acceptor. Field-assisted dissociation of these polaron pairs is a critical process in determining device performance.

Photovoltaic power conversion efficiency is the single most important performance indicator. This paper gives an overview of procedures to determine the efficiency with respect to standard conditions. The measurement theory and general procedures for determining the efficiency with respect to reference conditions are well understood. The engineering challenge of commercial or custom equipment to perform accurate efficiency measurements for all photovoltaic technologies is discussed. Accurately measuring the performance of multijunction devices requires adjusting the intensity and spectral content of the light source so that each junction generates the proper photocurrent. Organic devices often have time constants on the photocurrent in excess of 1 s. This poses a variety of problems when measuring the quantum efficiency under 1-sun illumination or measuring the current-voltage characteristics. Many photovoltaic cells have reversible and irreversible transients in the current and/or voltage. Module acceptance testing and qualification procedures often assume that these transients are not present. The sample with the highest efficiency may not produce the highest energy because the photovoltaic performance is a function of the spectral content of the light, total irradiance, and temperature-all of which are different in the "real world" than under standard reference conditions.

The photovoltaic characterization of triple-junction InGaP₂/GaAs/Ge solar cells is presented. Measurements made using a single light source solar simulator are compared with other measurements made using a multi-light source solar simulator that provides a close match to the air mass zero (AM0) solar spectrum. The output spectrum of the solar simulators has been measured, and two methods for calibrating the simulator output intensity haven been employed. The spectral response of the solar cells has been characterized through quantum efficiency measurements. These data are analyzed to determine the effect of the simulator spectrum on the measured photovoltaic response, and in particular, areas where spectral mismatch between the simulator and AM0 can lead to inaccurate performance predictions are highlighted. In addition, the effects of the different calibration techniques on the measured data are studied. Exploiting the capabilities of the multi-source, close matched simulator, the response of each of the three sub-junctions are studied individually, and the interplay between the spectral response of the sub-junctions and the incident spectrum is investigated.

Limited spectral response range of photocoltaic (PV) devices requires device performance be characterized with respect to widely varying terrestrial solar spectra. The FORTRAN code "Simple Model for Atmospheric Transmission of Sunshine" (SMARTS) was developed for various clear-sky solar renewable energy applications. The model is partly based on parameterizations of transmittance functions in the MODTRAN/LOWTRAN band model family of radiative transfer codes. SMARTS computes spectra with a resolution of 0.5 nanometers (nm) below 400 nm, 1.0 nm from 400 nm to 1700 nm, and 5 nm from 1700 nm to 4000 nm. Fewer than 20 input parameters are required to compute spectral irradiance distributions including spectral direct beam, total, and diffuse hemispherical radiation, and up to 30 other spectral parameters. A spreadsheet-based graphical user interface can be used to simplify the construction of input files for the model. The model is the basis for new terrestrial reference spectra developed by the American Society for Testing and Materials (ASTM) for photovoltaic and materials degradation applications. We describe the model accuracy, functionality, and the availability of source and executable code. Applications to PV rating and efficiency and the combined effects of spectral selectivity and varying atmospheric conditions are briefly discussed.

We present data on the initial period of operation of Gilch-route MEH-PPV/TiO₂ composite solar cells (CSCs) which show that during this period the CSCs operate in a non-steady state regime. The behavior is complex and may include a gradual rise of the open circuit voltage (V_oc) and of the short-circuit current density (J_sc) with time, a passage through a maximum of either or both parameters, and even a sign reversal. The mechanisms most probably contributing to the transient processes are: i) diffusion driven redistribution of charges resulting in the build up of a quasi steady state charge density profile across the device; ii) photo-doping resulting in a relatively slow increase of the average charge carrier concentration and consequently of the conductivity of the device. The latter is responsible for a strong decrease in Voc, and is evidenced by the significant increase in dark current after device illumination.

Control of charge interfacial charge transfer is central to the design of photovoltaic devices. A an elegant approach to control those dynamics, is the use of an insulating metal oxide blocking layer at a nanocrystalline inorganic / organic semiconductor interface. We show that the conformal growth of a ~1 nm thick overlayer of MgO on a preformed nanocrystalline SnO₂ film results in a ~4-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 sensitised nanocrystalline solar cells fabricated from such films, with the MgO coating resulting in ~ 50% improvement in overall device efficiency.

Different material combinations of two conjugated polymers, each blended with the methanofullerene acceptor phenyl-C₆₁ butyric acid methyl ester (PCBM) have been evaluated focusing on their potential for application as absorber material in polymer-fullerene bulk-heterojunction solar cells. Devices based on these solution processable composite materials have been studied by means of temperature dependent profiling of the photocurrent. In combination with measurements of the incident photon conversion efficiency, this technique probes the charge carrier recombination losses within the absorber material. Samples based on material composites with a low mobility-lifetime (μτ) product of the charge carriers (OC₁C₁₀-PPV: PCBM) exhibit a thermally activated photocurrent throughout the temperature range from 100 K to 350 K. The latter issue is attributed to the presence of shallow traps inside the bulk of the absorber limiting the photocurrent by recombination and scattering of the charge carriers with defects. Accordingly, the active layer thickness must be kept low at the expense of optical absorption. In contrast, the photocurrent in devices based on absorber materials with a high μτ product, P3HT: PCBM, saturates at a certain temperature and becomes constant, reflecting that all photogenerated charge carriers are efficiently extracted within their lifetime prior to recombination. Thus, solar cells with absorber materials demonstrating a high μτ product, have the potential to be designed with relatively thick absorber films above 100 nm. A large active layer thickness is a prerequisite for industrial deposition techniques, e.g., screen-printing, and improves the mechanical stability of large area flexible solar cells. As consequence of a high μt product the increase of the active layer thickness to L=350 nm in P3HT: PCBM photovoltaic devices results in a higher density of photogenerated charge carriers due to improved light absorption. Consequently, a strongly increased short-circuit current density of up to 15.2 mA/cm² was obtained for devices with absorber thickness of 350 nm which rising the power conversion efficiency up to 3.1 %.

Fluorene arylene copolymers are a class of aromatic macromolecules that have an alternating backbone structure consisting of a 9,9-dialkylfluorene together with one (or more) additional aromatic group(s). Fluorene when combined with chromophoric and/or charge transporting aromatic monomers to form polyfluorenes have received a great deal of attention over the last several years as the emissive layer in polymeric light emitting diodes. The emission of green, red, or blue light can be controlled by the choice of the aryl backbone segments and alkyl side groups in the polymer. More recently, polyfluorenes have been designed and evaluated as the organic semiconducting layer in polymeric field effect transistors (pFETs). This work has led to a class of polymeric semiconductors with an excellent combination of charge mobility, environmental stability, and processability. These polymers have also been shown to have optoelectronic properties. The high optical density, high charge carrier mobility, and the potential to tune the absorption spectra makes this class of materials an ideal candidate for further study in the area of organic photovoltaics. This paper reviews the synthesis and characterization of polyfluorenes, focusing on the optimization of electronic properties for the conversion of light into electric current.

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 organo-soluble copolyquinoxalines were used in polymer blends with poly-[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenvinylene] or regioregular poly-(3-hexylthiophene). The photovoltaic properties of these polymer blends depend on the blend morphology. So the short circuit current density can be improved by better solvent mixtures and by temper processes. But nevertheless the photovoltaic properties are low and a stable and well ordered phase morphology is difficult to obtain with polymer blend systems. Therefore another approach to receive more effective full polymer photovoltaic cells was done. Block copolymers consisting of n-type and p-type sequences in one polymer chain were synthesized. As n-type material a quinoline monomer and as p-type material 3-hexylthiophene were used. The synthesis of these new materials is described. The spectroscopic and cyclovoltammetric investigations clearly indicate their block copolymer structure. The study of their phase morphology and photovoltaic properties is in progress.

Organic photovoltaic cells exhibiting an ideal diode behavior with large fill factor (FF) are presented. It is demonstrated that the current-voltage characteristics can be well described using the equivalent circuit model that is also used for inorganic solar cells. Resistances associated with the cells and other diode parameters are extracted by fitting the experimental electrical characteristics using the equivalent circuit model. The effects of these parameters on FF are quantitatively described. Changes in these parameters under different illumination conditions are presented and compared to those occurring in inorganic pn-junction solar cells.

Single heterojunction and multi-heterojunction, small-molecule organic photovoltaic devices (OPVs) have been prepared on Glass/ITO and fully-flexible thermoplastic substrates using pre-patterned, conducting polymer electrodes (~ 450Ω/□). OPVs were fabricated via sequential vacuum vapor deposition of layers of the organic electron donating/hole transporting material: N,N'-(a-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (a-NPD) and the electron accepting/transporting material C₆₀. Devices built on glass/ITO substrates operated with a maximum, white-light power conversion efficiency (η_power) of 1.1% (AM1.5, 97 mW/cm²). Analogous devices fabricated on fully-flexible, plastic substrates using conducting polymer transparent electrodes exhibited white-light power conversion efficiencies of ~1%, virtually identical to those fabricated on prepatterned ITO/glass substrates. The glass/ITO cells were further optimized by including an exciton blocking layer of 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and their η_powerS exhibited a 30% increase to 1.3%.

Optimization of polymeric/organic solar cells in both space (morphology) and energy (time) domains has been preliminarily examined, both experimentally and theoretically, in order to minimize the 'photon loss', the 'exciton loss' and the 'carrier loss'. In spatial domain optimization, for instance, thin films of the -donor-bridge-acceptor-bridge- (-DBAB-) type block copolymer exhibited much higher photoluminescence quenching and photoconductivity in comparison to corresponding donor/acceptor simple blend films under identical conditions. This enhancement of photoelectric conversion was attributed mainly to the improved bicontinuous morphologies in the -DBAB- block copolymer versus the donor/acceptor simple blend. In energy/time domain optimization, preliminary theoretical simulation reveals that, an optimum exciton-charge conversion can be achieved when the frontier orbital offset of donor/acceptor pair is close to the sum of exciton binding energy and the charge separation reorganization energy.

Evaluating the performance of photovoltaic (PV) devices in the laboratory and in the field requires accurate knowledge of the optical radiation stimulating the devices. We briefly describe the radiometric instrumentation used for characterizing broadband and spectral irradiance for PV applications. Spectral radiometric measurement systems are used to characterize solar simulators (continuous and pulsed, or flash sources) and natural sunlight. Broadband radiometers (pyranometers and pyrheliometers) are used to assess solar resources for renewable applications and develop and validate broadband solar radiation models for estimating system performance. We describe the sources and magnitudes of uncertainty associated with calibrations and measuremens using these instruments. The basic calibration and measurement uncertainty associated with this instrumentaion are based on the guidlines described in the International Standards Organization (ISO) and Bureau INternationale des Poids et Mesures (BIPM) Guide to Uncertainty in Measurement. The additional contributions to uncertainty arising from the uncertainty in characterization functions and correction schemes are discussed and ilustrated. Finally, empirical comparisons of several solar radiometer instrumentation sets illustrate that the best measurement accuracy for broadband radiation is on the order of 3%, and spectrally dependent uncertainty for spectroradiometer systems range from 4% in the visible to 8% to 10% in the ultraviolet and infrared.

Efficient technique of Quantum Radiative Cooling (QRC) of textured Solar Cells and Modules is described that is capable of Solar Module (SM) temperature reduction by 5-20C, resulting in 3-10% efficiency increase. Novel methods are based on the quantum assisted IR emission from the surface covered by either multi-layer coatings made of Si-nitride, SiO or Si oxy-nitride films or specifically designed insulating sun-transparent chamber (QRC zone) that contains Selective Emissive (SE) gas or gas mix. QRC zone is mounted on the top of Solar Module replacing existing lamination coatings. To enhance the efficiency of QRC some specific methods and fabrication procedures are proposed to form an electricly charged textured surface that provide a high Electric Field at the surface thus enhancing IR emissivity from the surface. Such procedure can be also used to form the field Induced Surface Barriers in the Si-based Solar Cells that can substitute the existing diffused Emitters resulting in significant reduction of the Cycle Time as well as prospective Fabrication Cost.

Optimization of transparent conductive and textured-dielectric coatings to increase the efficiency and reflectance control is very important for solar cell applications. The developed technique has allowed us to obtain Li doped ZnO films with high transparency and low dark conductivivity. Measurements of dark and photoconductivity were carried out over a wide frequency range (0-10¹⁰ Hz). Photoelectric property studies have shown that with Li doping, it is possible to achieve an essential increase of photoconductivity. This phenomenon can be used for development of solid-state photodetectors in the UV range (290-340 nm). The current-voltage characteristics, current-optical power sensitivity and kinetics of rise and decay times of slow and fast components of the photoresponse were studied. It was found that the dark current and photocurrent have different conductivity mechanisms: hopping mechanism of charge transfer in the Hubbard model impurity band for dark conductivity current and drift mechanism of charge transfer in the conduction band for photoconductivity current.

A series of chlorotricarbonyl rhenium (I) bis(phenylimino)acenaphthene (Re-DIAN-X) complexes were used as the photosensitizers for photovoltaic cells. Unlike other transition-metal-based photovoltaic sensitizers that can only be prepared by solution method, these complexes are sublimable. Compared to other rhenium diimine complexes based on bipyridine or 1,4-diaza-1,3-butadiene ligands, these complexes have lower band gaps, which can be modified easily by changing the structure of the ligand. It allows the preparation of blend of metal complexes in order to broaden the sensitization region in UV-vis absorption spectrum. One of the complexes also shows bipolar charge transport character with relatively high charge carrier mobilities in the order of 10^-3 cm²V^-1s^-1. Multilayer heterojunction and bulk heterojunction devices with fullerene as the electron accepting molecule were prepared. For the bulk heterojunction devices, the fill factor and power conversion efficiency under AM 1.5 simulated solar light illumination were 0.51 and 1.29 %, respectively. The effects of changing the Re-DIAN/C₆₀ film thickness, Re-DIAN/C₆₀ ratio and variation of ligand structures in the bulk heterojunction devices were studied. The amount of photosensitizer and electron transport molecules may strongly affect the balance between the photon absorption, exciton formation, dissociation, and charge transport processes. Atomic force microscopic images showed that the complex dispersed evenly with fullerene molecules in solid state.

Solar cells based on poly(3-hexylthiophene) (P3HT) :TiO₂ nanocomposite films were investigated. We studied the influence of the nanoparticle concentrations and different nanostructures (spherical particles with size ~5 nm and ~20-40 nm, and rods with diameter ~10 nm and length ~40 nm) on the performance of the nanocomposite solar cells. PL quenching and improved external quantum efficiency (EQE) was observed for all the nanocomposite devices compared to that of pristine P3HT solar cells. However, TiO₂ (~5 nm spheres) and TiO₂ rods showed only small improvement in EQE. The small improvement for the 5 nm TiO₂ spheres was attributed to the lack of connectivity of nanoparticles for electron conduction. Therefore, the charge collection efficiency was limited. For TiO₂ rods, the tendency of the rods to lie in the plane of substrates also limited the charge conduction and collection in the direction perpendicular to the substrates. Therefore, the improvement of the devices made by these nanoparticles was limited. For TiO₂ (20-40 nm spheres) with optimal concentration, external quantum efficiency up to 15% and AM1 power conversion efficiency of 0.42% were obtained. The improvement in the efficiency was related to the improved morphology of the film and was attributed to the formation of percolation paths of TiO₂ for electron conduction.

The electrical and photoelectrical properties of photovoltaic cells, made by dispersing particles of copper phthalocyanine (CuPc) in a binder polymer (polycarbonate MK) and sandwiching between gold nad indium electrodes, have been studied. A complete study of the current as a function of voltage and temperature is carried out. At low voltages, the current in the forward direction varies exponentially with voltage. At higher voltages, two separate regions of ohmic and space charge limited conduction (SCLC) are observed. The latter process is controlled by an exponential distribution of traps above the valence band edge. Analysis of the results enables the determination of the important trapping parameters. Reverse characteristics are interpreted in terms of both the Poole- Frenkel and Schottky effects. Barrier heights and widths are determined as a function of applied voltage. The photovoltaic parameters of the cells are determined from the analysis of the current -voltage characteristics under illumination. Trap density and Schottky barrier built in potential are estimated from capacitance-voltage measurements.

In our study, the polycrystalline Si thin films were grown for solar cell applications by using the metal-induced growth (MIG) process. In this process, the poly-Si heteroepitaxally grows from the NiSi₂ or CoSi₂ layers which were formed by the reaction of Ni or Co with Si. Usually, due to the low absorption of light in the crystalline Si, light confinement is an important issue in thin film poly-Si solar cells. The MIG poly-Si thin films have some intrinsic features which assist the light absorption and light trapping. First, the top surfaces of the poly-Si films are relatively rough and have grain facets which reduce the light reflectance. In comparison, the Ni-induced Si film has hemisphere-shaped grain tops while Co-induced Si films have pyramid-shaped grain tops. The Ni-induced Si film has a rougher top-surface, so it appears to be darker under the optical examination compared to the Co-induced sample. This implies that more light may be absorbed in the Ni-induced Si film than in the Co-induced one. Second, in the MIG process, a thin metallic layer under the Si film was formed as a seed-layer for Si growth. This metallic layer could serve as a back contact and a back surface reflector. The above top and back surface structures are naturally formed and will allow MIG poly-Si to absorb the light more efficiently than other techniques. So far, the Schottky solar cell which was fabricated for the intent of MIG poly-Si film property studies has shown a J_sc of 12 mA/cm². By considering the Si film thickness of 5 μm and the photon absorption of 60% at this thickness, these data are reasonable.

Multi-junction solar cells have been used for the asteroid sample return mission spacecraft, MUSUES-C, since May 2003, their spectral response ranging from 350 to 1850 nm. To use a new generation of multi-junction solar cells in space during a long duration, we must precisely evaluate their characteristics by means of an ageing test and a performance test. To cope with these issues, we need a new type of solar simulator and we call it a multi-solar simulator. This paper describes a design method for an air mass zero (AM0) multi-solar simulator according to CIE 85 (TC2-17) 1989. The multi-solar simulator consists of three kinds of lamp: Mercury lamps with high brightness in the UV region, Xenon lamps in the visible region (VR), which are equipped with an IR cut-off filter at a wavelength of more than 780 nm, and halogen lamps in the IR region, which are equipped with a VR cut-off filter at a wavelength of less than 780 nm. We can realize the AM0 spectra without spikes in this method. Light rays from those lamps housed in optical lamp houses are superposed on a test plane for testing the multi-junction solar cells. In our simulator's performance, it is possible to achieve a beam of intensity of 1.4KW/m², a projection area of 2.5*2.5m², and a uniformity of ±15%. Because of the beam uniformity, an ellipsoidal mirror and a partial diffusion filter are installed in each lamp-house, an angle of 10° being achieved as a half divergence angle.

We have studied the photocurrent data of 20:80 wt% blends of poly(2-methoxy-5-(3’,7’-dimethyloctyloxy)-p-phenylene vinylene) (MDMO-PPV) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) bulk heterojunction solar cells. Two cases have been investigated: When only drift of charge carriers is taken into account, a voltage-independent photocurrent is expected, corresponding to the extraction of all generated charges. It is demonstrated that the experimental data are in disagreement with this prediction. However, when both drift and diffusion of charges are taken into account, the predicted photocurrent shows a different behavior: At low electric fields a linear behavior is predicted, which results from the diffusion of charges, followed by saturation at high fields. The agreement between the numerical result and the experimental data obtained from MDMO-PPV:PCBM cells is satisfactory when a charge carrier generation rate of G=1.6 × 10²⁷ m^-3s^-1 is used, showing the importance of diffusion at low fields, i.e., near the open-circuit voltage.

2d-hexagonal nanostructured sol-gel thin films were prepared by dip-coating method. A neutral surfactant Brij58 was used as template to produced channels into the film. The structure was identified by X-ray diffraction and TEM. Silver nanoparticles were obtained by spontaneous reduction process of Ag⁺ ions to Ag⁰ at room temperature. A broad band located at 430 nm was detected by optical absorption; it corresponds to the surface plasmon. Photoconductivity studies were performed on films with ions and with silver nanoparticles to characterize their mechanisms of charge transport in the darkness and under illumination at 420 and 633 nm wavelengths. Straight lines showing an ohmic behavior fit the experimental data. Films without colloids possess normal photoconductivity behavior. But films with colloids present an abnormal response. Transport parameters were calculated. The films with silver nanoparticles exhibit a photovoltaic effect stronger than the films without nanoparticles, except to high concentrations. A theoretical model is proposed to predict these processes as function of the silver concentration.

Though being much less efficient than silicon cells, organic solar cells exhibit a unique combination of interesting properties: low cost, flexibility, and the possibility of large surface coverage. Large progresses have been made over the last years using MDMO-PPV (Poly[2-methoxy-5-(3’,7’-dimethyloctyloxy)-1,4-phenylenevinylene) reaching efficiencies of 2.9% and recently efficiencies over 3%, using poly(3-hexyl thiophene). A great deal of research however has still to be invested to improve the current state of the art. Among the main key-points to be addressed are namely the stability and lifetime of such devices. We are currently working on bulk heterojunction solar cells made from MDMO-PPV and PCBM (methano-fullerene[6,6]-phenyl C₆₁-butyric acid methyl ester). Different batches of MDMO-PPV, originating from different synthesis modes (classical "Gilch" synthesis and "Sulphinyl" synthesis led by IMEC-IMOMEC) have been tested. Evolution of the power efficiency following continuous illumination (AM1.5, 80 mW.cm^-2) was characterized under controlled atmosphere of nitrogen. In parallel, photodegradation studies are also investigated and electrical modeling is under way in order to get a better understanding of the relations between photochemical and electrical parameters of the diode that can be deduced from I/V curves.

The optical properties of previously synthesized sulfone and methoxy substituted block co-polymers of poly-phenlyenevinylene (PPV) have been examined. An internal space charge field is formed which has been used to quench the luminescence intensity in these materials by separating optically generated excitons and electron-hole pairs. The absorption and emission spectra and the time dependence of the emission of donor and acceptor derivatized block co-polymers was measured and the quenching of the luminescence was observed and quantified. PPV materials with this internal field have potential applications as solar energy converters and photodetectors.

This study focuses on systems consisting of high hole-mobility MEHPPV based polymers or a fluorene-bithiophene co-polymer in contact with different nanocrystalline TiO₂ films. We use photoluminescence quenching, time of flight mobility measurements and optical spectroscopy to characterize the exciton transport, charge transport and light harvesting properties, respectively, of the polymers, and correlate these material properties with photovoltaic device performance. We find that the polymer properties with greatest influence on device efficiency are the polymer exciton diffusion length and absorption range, followed by the hole mobility. We have also studied the photovoltaic performance of these TiO₂/polymer devices as a function of active layer thickness. Device performances are significantly improved by introducing a PEDOT layer between the polymer and the top Au electrode and by reducing the thickness of the active layers. The optimized devices have peak external quantum efficiencies ≈ 40 % at the polymer's maximum absorption wavelength and yield short circuit current densities ≥ 2 mA cm^-2 for air mass (AM) 1.5 conditions (100 mW cm^-2, 1 sun). The AM 1.5 open circuit voltage reaches 0.64 V and the fill factor 0.43, resulting in an overall power conversion efficiency of 0.58 %.

Photovoltaic cells require deposition of a platinum layer at the cathode to serve as a catalyst for reduction of redox carriers in PV cells. Current dye-sensitized solar cells (DSSC) employ high temperature decomposition of chloroplatinic acid to give platinum islands. In order to produce DSSCs with plastic substrates, a low temperature platinum deposition process was developed. Initial experiments showed that platinum was deposited if Karstedt platinum catalyst solution in hexamethyldisilazane (HMDZ) was coated onto a substrate followed by heating under 150°C. PV cell performance of Karstedt-HMDZ-containing platinum was inferior to cells made with high temperature platinum. However, CODPtMe₂ (COD = 1,5-cyclooctadiene) was found to be a platinum precursor that led to PV cell performance equivalent to that obtained from high temperature platinum. Other precursors were evaluated as well including MeCpPtMe₃ that permitted platinum deposition via UV irradiation. Kelvin Probe analysis was also performed on several platinum films prepared from a variety of precursors on several substrates under a variety of conditions. CPD values of < -0.6eV appeared to predict good PV cell performance. Further application of the low temperature-derived platinum films was made for organic light emitting diodes.

We present this detailed study of a postproduction heat treatment of flexible organic solar cells based on regio-regular (RR) P3HT:PCBM composite in a wide temperature range from 75°C to 150°C. The efficiency of the photovoltaic device was significantly improved by postproduction heat treatment and both optimal annealing temperature and time dependencies were determined. Optimized parameters yielded >3% efficiency for devices on glass substrates and, using these optimized parameters, an efficiency of >2% was found for devices fabricated on flexible substrates. The optimal phase separation of PCBM and RR-P3HT into bi-continuous network structure occurs within a very short period of time and are very stable. We found that optimal concentration of PCBM in a RR-P3HT matrix is rather low, only 34 w.%. We show the performance of plastic solar cells fabricated on flexible substrates (ITO coated PET) using these optimized heat treatment parameters.