In superstrate thin-film solar cells light scattering is introduced by the surface texture of the transparent conductive front contact. However, a prerequisite to discuss light trapping in thin-film solar cells is a deeper understanding of the scattering behavior of such randomly textured substrates. The haze, which is widely used to characterize the scattering properties of randomly textured substrates, is an inadequate criterion to correlate the optical quality of the substrate and the measured short circuit current of solar cells. It will be shown that the wavelength dependence of the haze can be used to classify different kind of substrates. Furthermore, the angular resolved scattering properties are analyzed by means of ray tracing based simulation approach. The gained results reveal new aspects for the assessment of light trapping in thin-film silicon solar cells.

The potential of three advanced optical designs in tandem micromorph silicon solar cells are analysed by means of optical simulations: enhanced light scattering, intermediate reflector (interlayer) and antireflective coating (ARC) on glass. The effects on quantum efficiency, QE, and short circuit current density, J_SC, of the top and bottom cell are investigated. In case of enhanced light scattering, the role of haze parameter and angular distribution function of scattered light is analysed separately. High haze parameter improves light trapping in top and bottom cell. However, the improvement in QE and J_SC of the bottom cell is limited at higher haze parameters due to increased absorption in top cell and increased optical losses in realistic textured ZnO/Ag back contact. Broad ADF plays an important role for improving the performances of both, top and bottom cell. The role of refractive index of an interlayer between top and bottom cell is analysed. Significant increases in QE and J_SC of the top cell are revealed for small refractive indexes of the interlayer (n < 2.0). At the same time noticeable decrease in the performance of the bottom cell is observed. Optimisation of thickness and refractive index of a single-layer ARC on glass is carried out in order to obtain maximal J_SC either in top or in bottom cell. Moderate increases in J_SC and QE are obtained for optimised ARC parameters. Among the three optical designs, the greatest potential, considering the improvements in both cells, is revealed for enhanced light scattering.

The application of contactless transient photoconductivity measurements in the microwave frequency range for the optoelectronic characterization of Silicon-nitride covered Silicon samples for solar cells is investigated. It is shown that these measurements are a very sensitive tool for the study of the anti-reflection properties of Silicon-nitride films. The investigation of Silicon heterojunction solar cells shows that the illumination of the Silicon-nitride covered rear face of these heterojunctions may be a method to improve the efficiency of these solar cells.

Photovoltaic tandem and triple solar cells are currently being developed and produced with reasonable efficiencies at high technological cost. The concept of spectrum splitting has been proposed with the advantage of compatibility to all types of cells. Although additional optical efforts are to be made, external photon management can be achieved to match different solar cell combinations no matter which band gaps involved or how the cells are connected. We present an experimental study comparing optical devices based on either interference or diffraction for tandem and triple cell configurations. Whereas diffractive media such as gratings suffer intrinsically from higher order diffraction losses, devices based on interference such as Bragg filter can yield a significant efficiency increase. For a triple cell configuration consisting of GaInP/GaInAs/GaSb, a net efficiency gain of more than 30% is shown in a solar cell simulator compared to the best cell in direct light.

Thin-film silicon solar cells require an effective light trapping and a low reflectivity over the entire sun spectrum. As the optics in thin-film devices is not understood in detail optical simulations can be a useful tool to investigate the wave propagation in textured layer stacks. For microcrystalline (μc-Si:H) and amorphous (a-Si:H) silicon solar cells transparent conductive oxides (ZnO) with randomly rough textured interfaces are commonly used to achieve an improved light in-coupling into the cell and light scattering at the rough interfaces. Since periodically textured substrates offer the possibility to design the solar cell in accordance to a waveguide, the solar cells with integrated grating coupler and Bragg reflector gain more and more in importance. To get more insight into light propagation a detailed computational study focusing on the relation of the incoming light wave and the structure size and structure shape of the interface texture is extremely valuable.

Hydrogenated amorphous silicon has been widely studied last years, both from the basic research and industrial points of view, due to the important set of potential applications that this material offers, ranging from Thin Films Transistors (TFTs) to solar cells technologies. In different fabrication steps of a-Si:H based devices, laser sources have been used as appropriate tools for cutting, crystallising, contacting, patterning, etc., and more recent research lines are undertaking the problem of a-Si:H selective laser ablation for different applications. The controlled ablation of photovoltaic materials with minimum debris and small heat affected zone with low processing costs, is one of the main difficulties for the successful implementation of laser micromachining as competitive technology in this field. This work presents a detailed study of a-Si:H laser ablation in the ns regime. Ablation curves are measured and fluence thresholds are determined. Additionally, and due to the improved performance in optolectronic properties associated to the nanocrystalline silicon (nc-Si:H), some samples of this material have been also studied.

In natural photosynthesis, light is absorbed by photonic antenna systems consisting of a few hundred chlorophyll molecules. These devices allow fast energy transfer from an electronically excited molecule to an unexcited neighbour molecule in such a way that the excitation energy reaches the reaction centre with high probability. Trapping occurs there. The anisotropic arrangement of the chlorophyll molecules is important for efficient energy migration. In natural antennae the formation of aggregates is prevented by fencing the chlorophyll molecules in polypeptide cages. A similar approach is possible by enclosing dyes inside a microporous material and by choosing conditions such that the cavities are able to uptake only monomers but not aggregates. In most of our experiments we have been using zeolite L as a host because it was found to be very versatile. Its crystals are of cylindrical shape and consist of an extended one-dimensional tube system. They can be prepared in wide size range. We have filled the individual tubes with successive chains of different dye molecules and we have shown that photonic antenna materials can be prepared. Moreover, fluorescent dye molecules can be bound covalently to the channel entrances. Dependent on the spectral properties of these stopcock molecules, the electronic excitation energy is transported radiationless to the stopcock fixed at the ends of the nanochannels or injected from the stopcock to the dyes inside the zeolite. The radiationless energy migration is in competition with spontaneous emission, thermal deactivation, quenching, and photochemically induced degradation. Fast energy migration is therefore crucial for an efficient antenna material. - The supramolecular organization of the dyes inside the channels is a first stage of organization. It allows light harvesting within the volume of a dye-loaded zeolite L crystal and radiationless transport to both ends of the cylinder or from the ends to the centre. The second stage of organization is the coupling to an external acceptor or donor stopcock fluorophore at the ends of the zeolite L channels, which can trap or inject electronic excitation energy. The third stage of organization is the coupling to an external device via a stopcock intermediate. The wide-ranging tunability of these highly organized materials offers fascinating new possibilities for exploring excitation energy transfer phenomena, and challenges for developing new photonic devices for solar energy conversion and storage.

A nonlinearly of the photovoltaic conversion which depends on the light excitation has been observed on multi-interface Si devices provided with a nanoscale layered system. The effect has been visualized on the carrier collection efficiency. An analysis and simulation of the spatial collection components has been done. In the experimental part, two approaches are reported: the collection dependency on the equipment used and on the light excitation. First, the same test cell has been measured using two types of equipment in three different laboratories, respectively: 1) filters with light focalization and 2) monochromator. Next, the collection has been measured with different intensities of probing flux without any optical bias. The difference of the excitations used in the filter apparatus with a focused spot (having after focusing the near-solar intensity) can be roughly estimated as five orders of magnitude. We conclude that the nonlinearity of the photovoltaic conversion depends on the density of free carriers confined inside the surface zone due to a carrier collection limit. This limit appears with a nanoscale Si-layered system at the upper crystalline/amorphous interface. The same system introduces new carrier generation centers within the crystalline Si. These centers are at the origin of a low energy carrier multiplication which strength the nonlinearity. As shown in the paper the nanoscale Si transformations lead, for example, to a considerable infrared collection improvement. This suggests that Si solar cells with very high efficiency should be realizable using this way.

The luminescence quenching of the oxygen sensitive Ru²⁺ complex (Ru-ph4-TMS) used as a stopcock and attached to a zeolite L monolayer has been investigated. The luminescence lifetime of the attached Ru-ph4-TMS was the same under N₂ and under O₂ atmosphere. This remarkable result is attributed to the shielding provided by the channels of the zeolite L crystals arranged as a monolayer. The emitting ³MLCT state of the Ru-ph4-TMS stopcock is localized on the ligand bearing the phenyl groups forming the tail of this complex, which deeply penetrates into the zeolite L channel.

Microstructuring of polymer surfaces on optical spacers allows formation of reflective light traps. Such flexible reflectors can be combined with flexible polymer solar cells. We have demonstrated enhanced absorption using Lambertian and regular light reflectors, demonstrated via luminescence from fluorescent layers. Such light traps are suitable to use in combination with polymer solar cells incorporating transparent electrodes. The possibility to enhance the concentration of excited states and photogenerated charges through light trapping also helps to increase charge carrier mobility. These experimental results indicate that light confinement may be an alternative approach for boosting the efficiency of thin film conjugated polymer photovoltaics.

One key problem in optimizing organic solar cells is to maximize the absorption of incident light and to keep the charge carrier transport paths as short as possible in order to minimize transport losses. The large versatility of organic semiconductors and compositions requires specific optimization of each system. We investigate two model systems, the MDMO-PPV:PCBM blend and the P3HT:PCBM blend. Due to the small thickness of the functional layers in the order of several ten nanometers, coherent optics has to be considered and therefore interference effects play a dominant role. The influence of the thickness of the photoactive layer on the light absorption is investigated and compared with experimental data. The potential of an optical spacer which is introduced between the aluminium electrode and the photoactive layer to enhance the light harvesting is evaluated by optical modelling. Optical modelling becomes more complex for novel solar cell architectures based on nanostructured substrates. Exemplary optical simulations are presented for a nanoelectrode solar cell architecture.

In this study, we have investigated the possibility to realize different types of stacked, serially connected organic solar cells. First of all, we combined solution processed MDMO-PPV:PCBM or P3HT:PCBM and evaporated ZnPc-C60 bulk-heterojunction solar cells to achieved tandem cells exploiting the complementary absorption spectra of each single cells. Such devices exhibit open circuit voltages of 1V with a short-circuit current of approximately 5mA/cm² and a fill factor of 0.35 under simulated AM1.5 illumination. In the case of stacked, series connected cells with all active layers processed from solution, we observed a significant increase of the open circuit voltage in comparison with the single junction cells: Device fabricated from two bilayers comprising MDMO-PPV and PCBM as photoactive materials exhibit 1.28V open circuit voltage, 1.1mA/cm² short circuit current and a fill factor of 0.45 under simulated AM1.5 illumination.

In this paper we present detailed optical simulations of organic bulk-heterojunction solar cells built with inverted layer sequence as compared to the commonly used setup which is based on indium tin oxide (ITO) covered glass or plastic substrates and where the metal electrode is evaporated on top of the active absorber blend. The inverted setup may have production related advantages over the conventional setup, as the metal electrode is first evaporated onto the substrate and afterwards only wet chemical processes are needed. Additionally ITO can be replaced with a suited module concept. The effects of light trapping with an optical spacer, namely a transparent conductive layer between the absorber and the metallic electrode are investigated for the inverted setup. The results show that the insertion of an optical spacer does not increase the maximal obtainable short circuit current density and is only beneficial if a decrease of film thickness of the active absorber results in a higher internal quantum efficiency, open circuit voltage or fill factor. In the experimental section we show that the inversion of the layer sequence can be realised without any loss in device efficiency as compared to devices with the conventional layer sequence.

The production process of organic solar cells (OSCs) is investigated and the effects of parameter variations on experimental results are analysed with the Principal Component Analysis (PCA). This statistical method is applied to an exemplar data set, in which the materials' concentration in the absorber solution and the spincoating speed of the absorber solution were varied intentionally. In addition to the remaining production parameters, the time intervals between the steps were included in the analysis. A large part of the variance in the experimental results can be explained with the evaporation conditions, the spincoating speed and the concentrations in the absorber solution. The PCA also confirms that the OSC is a complex and interdependent system, where one has to analyse the influence of several parameters at the same time in order to understand their effects on the OSC properties. The PCA results will be used to focus further experiments on the identified key parameters.

High concentrator photovoltaic systems look for a remarkable reduction of cost in the production of electricity from solar radiation. This is possible thanks to an optical system which focus the light on a small solar cell. In this manner, high cost semiconductor material is substituted by potentially lower cost optical system. Since that, for this kind of solar modules, efficiency of optics system achieves a similar importance than solar cell itself. On the other hand to actually obtain the desired cost reduction, the cost of new elements and process needed must be low. The purpose of this work is to present the last advances in the industrialization of concentration PV modules based on TIR-R concentrator. To obtain a cost effective solution, the optics system is one of the key elements. Injection moulding technology gives the desired cost and quality requirements for the manufacturing of the optics system elements. The encapsulation process of the whole photovoltaic module for mass production is described. Optimization of encapsulation process of solar cell inside of secondary lens has been carried out. Over that optimized devices several optical efficiency measurements have been done. Individual concentrators have reach 69% optical efficiency. The combination of these concentrators with solar cells of 30-35% efficiency will give high concentration modules in the range of more than 20% electrical efficiency.

Converting energy from the sun's radiation into electrical current has been a reality for over 40 years but the efficiency derived from these devices has been low and not economically practical. With recent developments in solar cell technology, including multi-junction cells, conversion efficiency of nearly 40% has been demonstrated in the laboratory. The efficiency gain is due to the structure of the cell coupled with optics used to concentrate the sunlight onto the device. The concentrator design requires that the cell be uniformly illuminated to achieve the highest efficiency. Optical analysis software is used in the design and simulation of the system comprised of the solar radiation, optical concentrator and solar cell. This paper will describe the modeling of these concentrators and illustrate how the simulation can provide improved designs to achieve high illumination uniformity.

Luminescent concentrator (LC) plates with different dyes were combined with standard multicrystalline silicon solar cells. External quantum efficiency measurements were performed, showing an increase in electrical current of the silicon cell (under AM1.5, 1 sun conditions, at normal incidence) compared to a bare cell. The influence of dye concentration and plate dimensions are addressed. The best results show a 1.7 times increase in the current from the LC/silicon cell compared to the silicon cell alone. To broaden the absorption spectrum of the LC, a second dye was incorporated in the LC plates. This results in a relative increase in current of 5-8% with respect to the one dye LC, giving. Using a ray-tracing model, transmission, reflection and external quantum efficiency spectra were simulated and compared with the measured spectra. The simulations deliver the luminescent quantum efficiencies of the two dyes as well as the background absorption by the polymer host. It is found that the luminescent quantum efficiency of the red emitting dye is 87%, which is one of the major loss factors in the measured LC. Using ray-tracing simulations it is predicted that increasing the luminescent quantum efficiency to 98% would substantially reduce this loss, resulting in an increase in overall power conversion efficiency of the LC from 1.8 to 2.6%.

The thermodynamic limits of photovoltaic solar energy conversion by fluorescent collectors are examined theoretically and experimaentally. The maximum efficiency of a fluorescent collector corresponds to the Shockley-Queisser limit for a non-concentrating solar cell with a single band gap energy. To achieve this efficiency the collector requires a photonic structure at its surface that acts as an omni-directional spectral band stop filter. Such a band stop filter is also required to achieve the thermodynamic light concentration limit in a fluorescent collector. The potential of photonic structures for the efficiency enhancement of idealized and real fluorescent collectors is highlighted. Analysis of a fluorescent collector system ny spatially resolved light induced current measurements and by quantum efficiency analysis shows that the collection efficiency of a real fluorescent collector system increases by up to 30% with the help of a Bragg stack on top of the collector acting as a band stop filter.

β-FeSi₂ is an attractive semiconductor owing to its extremely high optical absorption coefficient (α>10⁵ cm^-1), and is expected to be an ideal semiconductor as a thin film solar cell. For solar cell use, to prepare high quality β-FeSi₂ films holding a desired Fe/Si ratio, we chose two methods; one is a molecular beam epitaxy (MBE) method in which Fe and Si were evaporated by using normal Knudsen cells, and occasionally by e-gun for Si. Another one is the facing-target sputtering (FTS) method in which deposition of β-FeSi₂ films is made on Si substrate that is placed out of gas plasma cloud. In both methods to obtain β-FeSi₂ films with a tuned Fe/Si ratio, Fe/Si super lattice was fabricated by varying Fe and Si deposition thickness. Results showed significant in- and out-diffusion of host Fe and Si atoms at the interface of Si substrates into β-FeSi₂ layers. It was experimentally demonstrated that this diffusion can be suppressed by the formation of template layer between the epitaxial β-FeSi₂ layer and the substrate. The template layer was prepared by reactive deposition epitaxy (RDE) method. By fixing the Fe/Si ratio as precisely as possible at 1/2, systematic doping experiments of acceptor (Ga and B) and donor (As) impurities into β-FeSi₂ were carried out. Systematical changes of electron and hole carrier concentration in these samples along variation of incorporated impurities were observed through Hall effect measurements. Residual carrier concentrations can be ascribed to not only the remaining undesired impurities contained in source materials but also to a variety of point defects mainly produced by the uncontrolled stoichiometry. A preliminary structure of n-β-FeSi₂/p-Si used as a solar cell indicated a conversion efficiency of 3.7%.

β-FeSi₂ defined as a Kankyo (Environmentally Friendly) semiconductor is regarded as one of the 3-rd generation semiconductors after Si and GaAs. Versatile features about β-FeSi₂ are, i) high optical absorption coefficient (>10⁵cm^-1), ii) chemical stability at temperatures as high as 937°C, iii) high thermoelectric power (Seebeck coefficient of k ~ 10^-4/K), iv) a direct energy band-gap of 0.85 eV, corresponding to 1.5μm of quartz optical fiber communication, v) lattice constant nearly well-matched to Si substrate, vi) high resistance against the humidity, chemical attacks and oxidization. Using β-FeSi₂ films, one can fabricate various devices such as Si photosensors, solar cells and thermoelectric generators that can be integrated basically on Si-LSI circuits. β-FeSi₂ has high resistance against the exposition of cosmic rays and radioactive rays owing to the large electron-empty space existing in the electron cloud pertinent to β-FeSi₂. Further, the specific gravity of β-FeSi₂ (4.93) is placed between Si (2.33) and GaAs ((5.33). These features together with the aforementioned high optical absorption coefficient are ideal for the fabrication of solar cells to be used in the space. To demonstrate fascinating capabilities of β-FeSi₂, one has to prepare high quality β-FeSi₂ films. We in this report summarize the current status of β-FeSi₂ film preparation technologies. Modified MBE and facing-target sputtering (FTS) methods are principally discussed. High quality β-FeSi₂ films have been formed on Si substrates by these methods. Preliminary structures of n-β-FeSi₂ /p-Si and p-β-FeSi₂ /n-Si solar cells indicated an energy conversion efficiency of 3.7%, implying that β-FeSi₂ is practically a promising semiconductor for a photovoltaic device.

In this work we have analysed the application of the Laser Beam Induced Current technique to obtain high resolution images of Dye Sensitized Solar Cells (DSSC). While this technique is widely used in the study of solar cells based on solid-state technology, its use is not so extended on DSSCs because of problems arising from the interaction between a focused laser beam and the biphase structure of such devices. We have studied the cell response to focused radiation and we have found that part of the current generated by a DSSC is caused by the activation of the radiated point while another part is generated by those points previously illuminated. Both parts of the signal have been analysed from a mathematical point of view to implement an algorithm for improving the LBIC images. When applied, the original LBIC images improve in clearness so that morphological differences can now be clearly distinguished.

The light harvesting enhancement observed when photonic colloidal crystals are integrated in dye sensitized titanium oxide solar cells is investigated herein. Such absorptance increment is explained in terms of slow photon propagation at certain ranges of wavelengths lying within the photonic pseudogap and partial localization in an absorbing layer placed onto the colloidal lattice. Based on those findings, not only recently reported experiments have been satisfactorily explained, but also new optical designs for the dye-sensitized solar cells (DSSC) are proposed. The new arrangement consists of piling up different lattice constant crystals leading to light harvesting enhancement in the whole dye absorption range. We provide the optimum structural features of such photonic crystal multilayer needed to achieve a photocurrent efficiency enhancement of around 60% with respect to standard dye-sensitized solar cells.

The role of the plasma frequency ω_p of conductors in their use for various solar energy and energy efficiency tasks, especially in transparent solar control window coatings, is analysed for a range of materials including noble and other metals, transparent compound conductors and the metallic phase of VO₂. Ways of adjusting ω_p for improved functionality are considered, including novel mesoporous metals and composites that can have an "apparent" or effective plasma frequency. While high ω_p is needed for high thermal infra-red (IR) reflectance and strong surface plasmon resonant absorption, it is not the only requirement. The location of inter-band terms relative to ω_p and the solar infra-red, effective bandwidth, and a high relaxation frequency can each alter these responses substantially. Two materials with elevated carrier relaxation rates, in one case when intrinsic, and in another due to mesostructure, are used to demonstrate this impact. Solar control and visible performance of a mesoporous gold film is analysed.

Switchable mirrors are thin films of metals or alloys which show a reversible transition from a reflecting metallic state to a transparent semiconducting state upon hydrogen exposure. We investigated the parameters which influence the kinetics of thin films of magnesium nickel alloys capped with a thin catalytic palladium layer. We found that the kinetics are strongly dependent on the composition of the films which is demonstrated by measurement of the transmittance and the reflectance of the substrate and the film sides during switching. In the case of the hydrogenation reaction this is because of the different hydride nucleation behavior of the layers. It is shown that this behavior is controlled by interface reactions during the deposition of the layers and by structural features. Nucleation at the substrate interface is believed to be due to heterogeneous nucleation of magnesium nickel hydride on MgO particles. This reaction is suppressed by alloying of magnesium and palladium at the magnesium palladium interface. Nucleation in the layer volume seems to be inhibited in the case of non crystalline magnesium nickel layers. All these features lead to fast hydrogenation kinetics and good optical properties in the hydride state for intermediate layer compositions.

Spectral properties of two-dimensional (2D) metal surface gratings are investigated to develop high performance solar selective absorbers and sky radiators. Numerical calculations based on rigorous coupled-wave analysis (RCWA) are performed and surface gratings are fabricated on silicon substrates by means of photolithography and etching process. Reflectivity spectra of the samples are measured and they show good spectral selectivity for each application. In order to fabricate surface microstructures in large area with low cost, direct metal imprinting technology are proposed. A microstructured nickel metal mold for the solar selective absorber surface is fabricated by means of electroplating technique and imprint experiments are performed on copper metal surface using mechanical pressing system. As a result, some parts of the surface structures are successfully transferred onto copper substrate.

We set up a high-temperature ellipsometry system for the measurement of optical constants n and k. The n and k values of refractory metals of W and Mo were measured from the visible (VIS) to near infrared (NIR) wavelength range at several temperatures by means of the system. The n drastically increases especially in the NIR region, while the k is almost invariant in all the range with increasing temperatures. Numerical simulation based on rigorous coupled-wave analysis (RCWA) with the values of n and k measured by high-temperature ellipsometry is qualitatively coincident with the measured spectral emissivity at high temperature. It has revealed that spectral emissivity has temperature dependence especially in the NIR region.

This study addresses the design of radio frequency (rf) magnetron sputtered aluminum doped zinc oxide (ZnO:Al) front contacts for silicon thin-film solar cells. Optimized films comprise high conductivity and transparency, as well as a surface topography trapping the light within the photovoltaically active layers. We have investigated the influence of the doping level of the target as well as the substrate temperature during sputter deposition on the ZnO:Al properties. The aluminum content in the target influences the transmission in the near infrared (NIR), the conductivity as well as the film growth of the ZnO:Al layer. The latter affects the surface topography which develops during wet-chemical etching in diluted hydrochloric acid. Depending on aluminum content in the target and heater temperature three different regimes of etching behavior have been identified. We have applied the ZnO:Al films as front contacts in thin-film silicon solar cells to study their light trapping ability. While high transparency is a prerequisite, the light trapping has been improved using front contacts with a surface topography consisting of relatively uniformly dispersed craters. We have identified low amount of target doping and high substrate temperatures as sputter parameters enabling high cell currents. Short-circuit current densities of up to 26.8 mA/cm² have been realized in μc-Si:H single junction cell with absorber layer thickness of 1.9 μm.

In solar control devices based on total internal reflection and microstructured surfaces, the Goos-Hänchen shift can lead to a significant decrease in the geometrical optical solar shading effect. The knowledge of the maximal size of the Goos-Hänchen shift for a specific geometry is an important information to estimate its effect on the desired function of the system. Quantitative measurements of the shift for optical wavelengths seems not feasible and analytical approaches are not suited to identify the maximal shift. By using newly developed numerical techniques, namely the rigorous coupled wave analysis (RCWA), the maximal Goos-Hänchen shift for given parameters can be determined.

Self-assembled monolayers (SAMs) of metal complexes are a central component of functional chemical systems for energy conversion like in e.g. the dye-sensitized photoelectrochemical solar cells or photocatalytic processes at semiconductor surfaces. In this context, scanning electrochemical microscopy (SECM) under illumination is a most valuable tool for the understanding of elementary processes of such systems. SECM comprises an ultra-microelectrode (UME), which is incorporated into a 3- or 4-electrode, respectively, electrochemical setup and which can be positioned with sub-micrometer resolution in 3 dimensions relative to a substrate. In our system, we used Pt-UMEs and dye-sensitized nano-structured electrodes as substrates. The substrate can be illuminated from the backside, which resembles working conditions of solar cell arrangements. The electrolyte consists of 2-methoxypropionitrile in conjunction with redox couples as they are used in dye-sensitized nano-structured solar cell. With this setup the photoelectrochemistry in close contact to the substrate surface initiated by the injection of electrons from the dye into the conduction band of the TiO₂ due to illumination at working conditions has been investigated. In this contribution we present the general principle of the method as well as an initial validation by relating photocurrents measured with the SECM and solar cell performances.

Efficient organic photovoltaic devices show many interesting properties, but share a common drawback, namely their instability in atmosphere. We report on a shelf lifetime study of solar cells based on blends of two widely used polymeric semiconductors with 1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61 (PCBM), encapsulated in a new flexible and transparent poly(ethylene naphthalate) (PEN)-based ultra-high barrier material. The barrier coating is entirely fabricated by plasma enhanced chemical vapor deposition (PECVD). The conjugated polymers used are poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene-vinylene) (MDMO-PPV) and poly(3-hexyl)thiophene (P3HT). We have observed in this work that the encapsulation raises the shelf lifetime (50 % of the initial efficiency) from a few hours into the range beyond 3,000 hours for MDMO-PPV based devices. Using the more stable P3HT, the lifetime could be increased to approximately 6,000 hours, or more than eight months.

In this contribution, we present a new hybrid solar cell design. CuInS₂ nanoparticles were synthesized using a low temperature colloidal route with organic surfactants to form an inorganic nanoporous hole transporting electrode. A soluble fullerene derivate PCBM (1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6) C₆₁) was used for electron transport. We investigated the photovoltaic performance of the cells consisting of these CuInS₂ and PCBM bilayers with and without a surface-adsorbed RuL₂(NCS)/TBA(2:2) dye complex(where L= 2,2'-bipyridyl-4,4'-dicarboxylic acid; TBA= tetrabutylammonium). The cells containing the dye showed an improved photovoltaic response.

A surprising photovoltaic (PV) conversion at 400 nm has been observed in nanoscale Si-layered systems (ns-Si-ls) during spectral response measurements. In conventional solar cells the UV and blue PV conversion may be poor because of the surface recombination within a thin superficial layer. In multi-interface novel devices (MIND) containing ns-Si-ls this conversion is always negligible within an even thicker surface dead zone from which practically no free-carriers can be collected. So the measured 400 nm band PV conversion in MIND cells is totally inconsistent with usually observed effects. Another CE paradox concerns its inversely proportional variation versus incident flux intensity, lower the intensity higher the CE, which value can even exceed unity. This new effect is also localized at the superficial nanostratum and originates from postimplantation defects and nanostructures formed during the implantation process. A similar low energy free-carrier generation has been observed recently in MIND cells with buried ns-Si-ls having a relatively very thin superficial stratum because of an excellent electronic passivation. No available publication mentions such an effect despite extensive investigations on the subject of structural and optical properties of Si nanoparticles, Si nanolayers, new Si-based materials such as semiconductor silicides and the luminescence-center doped Si materials. In this work, the carrier collection properties of the superficial Si nanostratum are reported and discussed in detail in relation to incident flux intensity. An additional low energy generation was observed experimentally. The effect could have capital importance for a breakthrough in the PV conversion efficiency in Si solar cells with nanotransformations.

Multi-interface novel devices (MIND) exhibit a dramatically low UV- and blue-spectrum photovoltaic (PV) performance. A paradox could even be observed, the better the electronic passivation the poorer the PV performance. The paradox appears under relatively low excitations in comparison with intense laser fluxes usually at its origin. The effect can be explained by solar light induced opacity, which reduces considerably or even totally the photon penetration into deeper layers, from which exclusively the photocarrier collection is possible. This opacity results from a feedback occasioned by the free-carrier absorption: better surface passivation, higher free-carrier density, stronger surface dead zone absorptance. The total energy of the incident short wavelength beam can be absorbed before a carrier collection limit buried in the emitter. This limit acts simultaneously on the electronic performance, blocking free-carriers, and on the optical performance, being at the origin of an enhancement of the surface absorptance. As a consequence, a thin surface zone dominates the optical functions of MIND cells through the free-carrier gas confined inside it. In this work we report specific effects concerning the solar-light induced opacity in MIND cells. The investigation allows modification of the free-carrier confinement using different device architectures. The main characterization methods were reflectivity and spectral response with a varying incident beam. The results prove the domination of the free-carrier optical functions on the MIND PV conversion.

As solar cell production grows with record rates of approximately 30-40 % per year for the last 5 years the market starts to awake interest at various industries. Especially the laser technology seems to gain influence on the production sequence as more sophisticated solar cell concepts like laser-fired contacts (LFC), metal- / emitter-wrap through cells (MWT /EWT) or back junction solar cells are about to be industrially applicable. This paper gives a short introduction over the current situation of the solar cell market and the state of the art technology. Furthermore future cell concepts are explained briefly, where the main focus is set on the chances for laser technology to be implemented. Additionally the specific demands of the solar cell production are mentioned and all potentially possible laser processes rated with respect to their potential of being transferred into industry.

Semiconductor iron-disilicide (β-FeSi₂) is expected to be used for thin film solar cells owing to its direct band gap (around 0.85eV) feature and high optical absorption coefficient (α) that is higher than 10⁵cm^-1. To fabricate β-FeSi₂ solar cells on Si substrates, thick Si substrates are needed, and cost reduction is hard to be accomplished. This paper shows the possibility to use non-Si substrates such as insulating materials or metal sheets for replacing the Si substrates. SOI, fused quartz and CaF₂ single-crystal were used as non-metal substrates, and Mo, Ta, W, Fe and stainless steel sheets were used as metal substrates. Growth of β-FeSi₂ thin films was carried out with changing substrate temperature by facing-target sputtering (FTS) method. Formation of β-FeSi₂ thin film was characterized by XRD and Raman scattering observations. Adhesion force of the films to the substrates was evaluated by pealing test and electrical properties were examined by Seebeck and Hall effects measurements. Results showed that stainless steel and iron sheets become good substrates for the growth of β-FeSi₂ thin films. Peeling tests and SEM surface observations of these films stated that the adhesion force of these films to iron sheet and to stainless steel sheet is satisfactorily strong. Results of films deposited on the remaining substrates indicated that formation of β-FeSi₂ thin films was not clearly identified, and those films were easily removed from the substrate.