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We evaluate the potential of three-dimensional (3D) thin-film silicon solar cells in the superstrate configuration deposited on hexagonally ordered arrays of ZnO nanocolumns (NCs). These nanostructures are prepared by hydrothermal growth, which is an effective and versatile method to obtain ZnO NCs of high optical and electrical quality at low temperature. For the periods P investigated, varied between 0.9 and 1.4m, 3D solar cells based on hydrogenated amorphous silicon (a-Si:H) exhibit a photocurrent (J(SC)) boost in the red wavelength range as compared to flat cells; this J(SC) gain (by more than 1.5mAcm(-2) for P=0.9m) is explained mostly by the increased effective optical thickness of the absorber layer grown on the vertical walls of the NCs. Combining this 3D concept with randomly textured interfaces, rigorous 3D optical simulations based on the finite element method predict that photocurrents significantly higher than those obtained with state-of-the-art substrates (up to 20mAcm(-2)) are within reach, if the experimental obstacles specific for 3D design are overcome.

We report on the hydrothermal growth of high quality arrays of single crystalline zinc oxide (ZnO) nanocolumns, oriented perpendicularly to the transparent conductive oxide substrate. In order to obtain precisely defined spacing and arrangement of ZnO nanocolumns over an area up to 0.5 cm 2 , we used electron beam lithography. Vertically aligned ZnO (multicrystalline or single crystals) nanocolumns were grown in an aqueous solution of zinc nitrate hexahydrate and hexamethylenetetramine at 95 °C, with a growth rate 0.5 ÷ 1 μm/h. The morphology of the nanostructures was visualized by scanning electron microscopy. Such nanostructured ZnO films were used as a substrate for the recently developed 3-dimensional thin film silicon (amorphous, microcrystalline) solar cell, with a high efficiency potential. The photoelectrical and optical properties of the ZnO nanocolumns and the silicon absorber layers of these type nanostructured solar cells were investigated in details.

In this paper we have shown that it is possible to modify and control the surface morphology of doped SnO2 transparent conducting oxide thin films deposited by atmospheric pressure Chemical Vapour Deposition by use of additives during the deposition process. A range of volatile organic compounds were explored, which caused changes of differing magnitude to the growth rates, crystallographic preferences, size and shape of the surface features and optical transmittance. Of the additives tested methanol and tertiary butanol were found to have the most significant influence allowing the surface to be modified from small, round features to much more elongated, sharp, pyramidal features.

The standardized techniques to characterize the optical properties of thin films are of high importance for development, optimiza-tion and reliable production of thin film solar cells. We apply op-tical transmittance & reflectance spectroscopy, photothermal de-flection spectroscopy (PDS) and laser calorimetry (LC) to evalu-ate optical absorption losses at rough interface between rough thin conductive oxide (TCO) and metal films used as backreflec-tors and electrical contacts in thin film solar cells. The dielectric function of the rough metal can be calculated in Landau-Lifshitz-Looyenga model fitting only one unknown parameter which greatly simplifies modelling of the optical properties of thin film solar cells.

Toxic gas sensing device with metal electrodes built into nanocrystalline diamond (NCD) is investigated. The NCD morphology is controlled via seeding and/or deposition time. The surface properties and morphology of NCD are studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). AFM measurements reveal increase in NCD surface area by up to 13%. Gas sensing properties of H-terminated NCD device show high sensitivity towards oxidizing species where the surface conductivity is increased by an order of magnitude for humid air and by three orders of magnitude for COCl 2 . The surface conductivity exhibits a small decrease to reducing spices (CO 2 , NH 3 ).

Nanocrystalline diamond (NCD) thin films and structures are grown by microwave plasma CVD technique on SiO 2 /Si substrates patterned by polymer. The substrates are seeded by ultra-dispersed diamond (UDD) nanoparticles in polymer, by spin coating of UDD drop and by ultrasonic treatment in solution of UDD. For all samples, the deposited NCD film is strongly related to the primary polymer deposited over the Si/SiO 2 substrate. For a certain concentration of UDD, seeding by polymer composite results in formation of fully closed layer. The drop of UDD requires using of spin coating process and by repeating of this procedure, a NCD layer with clear 3D geometry is achieved. Ultrasonic treatment leads in “implanting” of UDD into the polymer bulk. The primary polymer stripes are damaged during this procedure. In addition, 3D porous like layer is observed after the CVD growth. Optimizing the seeding procedure and the dimension of the primary polymer allow a direct growth of self-standing air bridges suitable for MEMS/NEMS applications.

The potential of thin film photovoltaic technologies in supporting sustainable energy policies has led to increasing interest in high performance transparent conducting oxides (TCOs), and in particular doped SnO2, as electrical contacts for solar cells. We have developed an advanced atmospheric pressure chemical vapour deposition process, by applying fast experimentation and using a combinatorial chemistry approach to aid the studies. The deposited films were characterised for crystallinity, morphology (roughness) and resistance to aid optimisation of material suitable for solar cells. Optical measurements on these samples showed low absorption losses, less than 1% around 500 nm for 1 pass, which is much lower than those of industrially available TCOs. Selected samples were then used for manufacturing single amorphous silicon (a-Si:H) solar cells, which showed high solar energy conversion efficiencies up to 8.2% and high short circuit currents of 16 mA/cm2. Compared with (commercially available) TCO glasses coated by chemical vapour deposition, our TCO coatings show excellent performance resulting in a high quantum efficiency yield for a- Si:H solar cells.

In this paper we report the results of a study assessing a newly developed deposition process for Fdoped SnO2 films by CVD operating at atmospheric pressure (APCVD). The technology is designed to be compatible with industrial requirements such as high process speed, possible up-scaling to wide substrate widths and low costs. The optical and electrical properties of layers deposited on glass are found to be similar to those of commercially available lowpressure CVD. Optical absorptance below1% is achieved for films of around 0.8�mthick. Such transparent conductive oxide (TCO) is used with a-Si:H single junction p–i–n solar cells grown by PECVD. The cells are characterised by I–V measurements using AM1.5 spectra and by measuring the external quantum efficiencies (EQE). The initial efficiencies were up to 9.3% with FF = 73%. The TCO films demonstrated an enhanced performance in the EQE compared to commercially available TCO (Asahi-U).

Nanocrystalline diamond thin films are grown on silicon and glass substrates by microwave plasma (MP)CVD from a gas mixture of methane and hydrogen at low substrate temperatures. The initial stages of diamond growth, i.e., i) the growth of individual nanometer-sized crystals and clusters, and ii) coalescence into a continuous layer, are investigated by diverse analytic techniques. Atomic force microscopy (AFM) measurements reveal nearly unchanging surface roughness up to 40 min. X-ray photoelectron spectroscopy (XPS) measurements detect changing of the surface composition from the very beginning of the growth process. The rapid carbon increase is assigned to the enlarging of the grown crystals and clusters. Scanning electron microscopy (SEM) images indicate a possible lateral growth type. The found dependences indicate that a two-dimensional growth mode takes place at low substrate temperatures. Grown nanocrystalline diamond films are optically transparent in a wide spectral range, and exhibit a high refractive index of 2.34.

The broad optical spectral range (0.2–6 eV) photoionization spectra of the nominally undoped, carefully oxidized and hydrogenated nanocrystalline diamond (NCD) thin films grown on silicon and sapphire substrates were measured using the dual-beam photoconductivity method (under constant UV light bias). The novel amplitude modulated step scan Fourier transform photocurrent spectroscopy (AMFTPS) was applied in IR region. The wet chemistry etching was used to open 6 × 6 mm window in Si substrate and to create NCD membrane in the silicon frame. In photoionization spectra we found localized defect states with the threshold around 1 eV in both hydrogenated and oxidized NCD films. The threshold of the photoionization cross section shifts towards lower photon energies in the hydrogenated samples. The photosensitivity increases by several orders of magnitude with hydrogenation. We suggest that the main deep defect is related to the nanocrystalline grain boundaries and it can be passivated by the hydrogen. In hydrogenated samples we detect at low temperature shallow defect states with photoionization threshold energies well below 1 eV, probably related to the hydrogenated surface.

The paper summarizes progress in the Fourier transform photocurrent spectroscopy (FTPS) since 2001 when it was introduced for the first time for evaluation of the spectral dependence of the optical absorption coefficient in microcrystalline silicon thin films. We concentrate on the appropriate measuring conditions and evaluation procedures for a correct data interpretation of various thin films and solar cell structures. We show how the measured and finally evaluated absorption spectra differ in case of single junction amorphous and microcrystalline silicon solar cells as well as for a micromorph tandem. The key issue of the tandem structure diagnostics is a separation of FTPS signals from amorphous and microcrystalline parts of a stacked structure and their correct interpretation. For an appropriate simulation of the light propagation within the structure and confirmation of our measuring approach the computer model cell has been used.

Three types of materials modified with carbon particles were prepared: (1) carbon fibre-reinforced carbon composites (CFRC), materials promising for hard tissue surgery, coated with a fullerene C 60 layer, (2) terpolymer of polytetrafluoroethylene, polyvinyldifluoride and polypropylene mixed with 4 wt.% of single- or multi-walled carbon nanotubes and (3) nanostructured or hierarchically micro- and nanostructured diamond layers deposited on silicon substrates. The materials were seeded with human osteoblast-like MG 63 cells (density from 8500 cells/cm 2 to 25,000 cells/cm 2 ). On the fullerene layers, the cells (day 2 after seeding) adhered in numbers from 2.3 to 3.5 times lower than those on control non-coated CFRC or polystyrene dishes. However, their spreading area was larger by 68% to 145% than that on the control surfaces. These cells also assembled numerous dot-like vinculin-containing focal adhesion plaques and a rich fine mesh-like beta-actin cytoskeleton. Similar results were obtained on the terpolymers mixed with carbon nanotubes. The cells were well spread and contained distinct beta-actin filament bundles, whereas the cells on the pure terpolymer were often rounded and clustered into aggregates. An enzyme-linked immunosorbent assay revealed that the cells on the material with single-walled carbon nanotubes contained a higher concentration of vinculin and talin, i.e. components of focal adhesion plaques (by 56% and 35%, respectively, compared to the pure terpolymer). However, the concentration of osteocalcin, a marker of osteogenic differentiation, was lower in cells on the terpolymer containing multi-walled nanotubes, which was probably due to more active proliferation of these cells (on day 7, they reached a 4.5 times higher population density than cells on the unmodified terpolymer). Adding both single-and multi-walled nanotubes to the terpolymer did not increase the concentration of ICAM-1, a marker of immune activation, in MG 63 cells. On diamond layers, the number of initially adhered cells was higher on the nanostructured layers, whereas the subsequent proliferation was accelerated on the layers with a hierarchical micro-and nanostructure. Thus, all tested carbon nanoparticle-containing materials gave good support to adhesion and growth of bone-derived cells, and they can be considered as promising for construction of bone implants and bone tissue engineering.

Steady state and low frequency photocurrent spectroscopies have proved as a valuable tool for investigation of many different semiconductors, used for example as an absorber in photovoltaic solar cells or in the large area sensors. Fourier transform photocurrent spectroscopy (FTPS), described here, exhibits advantages as a high sensitivity (we demonstrate dynamical range up to 9 orders of magnitude of the optical absorption coefficient, connected with the absorption process leading to free carriers; or sensitivity for dopant detection better than 1 part-per-billion), fast acquisition of data (it can be of the order of seconds) or high resolution (under more lengthy acquisition of data). Results on amorphous silicon, microcrystalline silicon, diamond layers, nanocrystalline diamond and very thin organic films, as poly(2-methoxy-5-(3′,7′-dimethyl-octyloxy))-p-phenylene-vinylene (MDMO-PPV), regioregular poly(3-hexylthiophene (P3HT) and their blends with (6,6)-phenyl-C61-butyric-acid (PCBM) are reported, together with the results measured on various thin film silicon or polymer solar cells.

Glass slides (standard 1 × 3 in. size) coated with nanocrystalline diamond were successfully tested for DNA immobilization. The nanodiamond films were grown on glass substrates at temperature below 400 °C, while keeping the excellent material properties of diamond, such as low background luminescence and high optical transparency. The nanodiamond surface to which proteins were attached was functionalized by ultra-thin amino-polymer film in the radio-frequency (RF) plasma discharge of vaporized organosilane coupling agent N -(6-aminohexyl) aminopropyl trimethoxysilane (AHAPS). Several different IR spectroscopy methods (transmission and reflection–absorption spectroscopy (IRRAS), attenuated total reflectance (ATR) and grazing angle reflectance (GAR)) are discussed with respect of their ability of detecting the functional groups on bio-functionalized diamond surface. The IR absorbance spectra of just a few nm thick RF plasma polymer films deposited on nanodiamond surface are presented.

We present investigation of nanocrystalline diamond films deposited in a wide temperature range. The nanocrystalline diamond films were grown on silicon and glass substrates from hydrogen based gas mixture (methane and hydrogen) by microwave plasma CVD process. Film composition, nano-grain size and surface morphology were investigated by Raman spectroscopy and scanning electron microscopy. All samples showed diamond characteristic line centred at 1332 cm − 1 in the Raman spectrum. Nanocrystalline diamond layers revealed high surface flatness (under 10 nm) with crystal size below 60 nm. Surface morphology of grown films was well homogeneous over glass substrates due to used mechanical seeding procedure. Very thin films (40 nm) were successfully grown on glass slides (i.e. standard size 1 × 3″). An increase in delay time was observed when the substrate temperature was decreased. A possible origin for this behaviour was discussed.

Nanocrystalline diamond (NCD) films were grown by microwave plasma CVD in hydrogen-based gas mixture. Deposition experiments were performed at different temperatures varying from 370 to 1100 °C. Before growth step, silicon (100) oriented substrates were nucleated by bias enhanced nucleation procedure and glass substrates were pretreated in ultrasonic bath. Optical, structural and morphological properties of NCD films were systematically studied by using an optical spectroscopy, scanning electron microscopy and Raman spectroscopy. NCD films were optically transparent in wide range and had high refractive index of 2.34. All deposited samples exhibited diamond characteristic line in the Raman spectrum. The growth kinetic was attributed to the hydrogen abstraction model.

Micro-cantilevers are excellent tools to measure tiny forces (from 1 nN up to 10 (iN) as shown by the development of atomic force microscopy (AFM) techniques. That is the reason why micro-cantilevers are also the most sensitive acoustic sensors. For instance, one can use the variation of the cantilever's resonant frequency to measure mass loading. In this work, we will show first why diamond is the most suitable material for a special type of cantilever sensors: piezoelectric bimorph cantilever sensors. In contrast to other cantilevers, it is possible to actuate piezoelectric bimorph cantilevers and to detect their resonance frequencies simultaneously. Then, we present one application of this type of cantilever: a diamond/AIN cantilever used as a high pressure sensor (up to 7 ar). The sensor operates by monitoring the frequency shift of the first resonant mode (f 1 ∼ 36.5 kHz). We have measured a sensitivity of 0.155 Hz/mbar in pure nitrogen.

Fourier transform photocurrent spectroscopy (FTPS) has been applied to the study of electronic defect states in nanocrystalline diamond films. To analyze the influence of the substrate on submicron-thin nanodiamond films, silicon substrates were compared to low alkaline glass substrates. We have observed four peaks in the photocurrent spectrum of nanocrystalline diamond: two sharp peaks at 0.36 and 0.40 eV and broad bands at 0.27 and 0.57 eV. These peaks, observed for films grown on Si substrate, have different behavior with respect to the temperature, external light illumination and absorption/desorption processes at the nanodiamond surface.

We have grown a variety of thin nanocrystalline diamond thin layers on silicon substrates with thicknesses ranging from 100 to 2000 nm. Using a bias enhanced nucleation for nucleation density over 10 10 cm −2 and changing the deposition conditions and/or using argon dilution we have obtained nanodiamond layers of different structural properties. The nucleation process and growth was monitored with Scanning Electron Microscopy (SEM); cross-section SEM and micro-Raman measurements were used to access the nanodiamond microstructure. Surface topography was followed by SEM and Atomic Force Microscopy. Windows were opened in the silicon substrate to get self-supporting diamond membrane. Diamond membranes are very smooth, homogeneous and transparent from UV to IR. Fourier Transform Photocurrent Spectroscopy has been used to access main electronic defects in the gap of this material. New defects were observed with a peak photoionization energy of 0.37 and 0.40 eV.

For thin film silicon solar cells and modules incorporating amorphous (a-Si:H) or microcrystalline (μc-Si:H) silicon as absorber materials, light trapping, i.e. increasing the path length of incoming light, plays a decisive role for device performance. This paper discusses ways to realize efficient light trapping schemes by using textured transparent conductive oxides (TCOs) as light scattering, highly conductive and transparent front contact in silicon p–i–n (superstrate) solar cells. Focus is on the concept of applying aluminum-doped zinc oxide (ZnO:Al) films, which are prepared by magnetron sputtering and subsequently textured by a wet-chemical etching step. The influence of electrical, optical and light scattering properties of the ZnO:Al front contact and the role of the back reflector are studied in experimentally prepared a-Si:H and μc-Si:H solar cells. Furthermore, a model is presented which allows to analyze optical losses in the individual layers of a solar cell structure. The model is applied to develop a roadmap for achieving a stable cell efficiency up to 15% in an amorphous/microcrystalline tandem cell. To realize this, necessary prerequisites are the incorporation of an efficient intermediate reflector between a-Si:H top and μc-Si:H bottom cell, the use of a front TCO with very low absorbance and ideal light scattering properties and a low-loss highly reflective back contact. Finally, the mid-frequency reactive sputtering technique is presented as a promising and potentially cost-effective way to up-scale the ZnO front contact preparation to industrial size substrate areas.

We present an optical model for thin-film silicon solar cells (both single and multijunction) with nanorough surfaces/interfaces. For these cells, the optical absorptance within each layer and the total reflectance are computed taking into account roughness, angular distribution of scattered light, thicknesses, and optical constants of all layers. In the model, we combine coherent approach, scattering theory, and Monte Carlo tracing method. Results of the model are shown to be in good agreement with the experimentally measured spectral response and the total reflectance of solar cells. Some predictions of the ultimate solar cell performance based on the model are presented as well.

Fourier-transform photocurrent spectroscopy (FTPS) was used as a sensitive spectroscopic method to study boron doping in diamond layers, deposited by microwave plasma enhanced chemical vapor deposition (CVD). Results were compared to boron doped single crystals, synthesized at high pressure and high temperature. Introduction of boron increases the photosensitivity of diamond; the measured spectrum of excited states of the boron acceptor depends both on the crystal perfection and the boron concentration. The spectrum of excited states is a clear fingerprint of the presence of substitutional boron (up to 31 absorption lines have been identified). A quantitative assessment of the substitutional boron concentration is possible and the sensitivity of FTPS in combination with photothermal ionization spectroscopy (PTIS) for boron detection in diamond is estimated to be better then 1 part per billion (ppb).

In combination with CVD diamond, an aluminium nitride (AlN) thin film is one of the most promising piezoelectric materials for surface acoustic wave (SAW) applications. One of the critical issues of SAW devices is the electromechanical coupling coefficient, which depends on the AlN film thickness and its mechanical and piezoelectric properties. In this work, properties of well (002) oriented AlN films deposited on silicon and fused quartz substrates by reactive DC pulsed magnetron sputtering were measured. The mechanical, electromechanical and optical properties of AlN film deposited under optimal conditions were determined. Novel methods, using an atomic force microscope (AFM), were used to measure the d 33 and d 31 piezoelectric coefficients. The d 33 piezoelectric coefficient measurement method allows a direct piezoelectric mapping. The experimental measurement results are in good agreement with the bulk values.

Polycrystalline diamond thin films were grown on 2-inch silicon wafers at high pressures, up to 250 mbar, in high power microwave plasma CVD rotational ellipsoidal reactor. Influence of the gas pressure and the gas mixture on the diamond growth was investigated. High growth rates, up to 4.5 μm/h, were obtained at high pressure and low methane concentration. Hydrogen desorption from the diamond surface under atomic hydrogen flux were found to limit diamond deposition rate and the activation energy of this process is 0.2 eV. During deposition, the growth temperature is monitored with a two-colors pyrometer. The observed variation of the apparent temperature was related to the diamond film thickness and the instantaneous deposition rate. Diamond layers were characterized by Raman spectroscopy, scanning electron microscopy and X-ray photoemission spectroscopy. New absorption peaks were observed in the spectra of Fourier transform photocurrent spectroscopy.

Raman scattering, X-ray photoemission spectroscopy (XPS), Fourier transform photocurrent spectroscopy (FTPS), Rutherford backscattering (RBS) and electron paramagnetic resonance (EPR) method have been used for characterization of diamond layers deposited by microwave plasma enhanced chemical vapor deposition (MWPECVD). As substrates, thick silicon wafers pretreated by the mechanical seeding have been used, surrounded by the molybdenum ring. Here we report how this configuration can lead to the Mo contamination of diamond layers (similar effect to the well known contamination of diamond by Si) and we study the optical spectra related to the presence of molybdenum and other impurities over the bulk of deposited layers. Mo contamination was confirmed by XPS measurements, but we were not able to detect it by RBS and EPR.

Fourier-transform photocurrent spectroscopy (FTPS) was used as a very sensitive spectroscopic method to detect shallow and deep impurities (dopants) in CVD diamond layers. Detailed study of experimental conditions (temperature, frequency, electric field, bias light, surface conditions) was performed. Residual boron contamination was detected in many samples, phosphorus spectra were measured in P doped epitaxial layers. Anomalous (opposite) temperature dependence of the defect level with a threshold approximately 0.9 eV was detected and possible explanation of this effect was discussed.

The structure of a-Si:H, deposited at rates in excess of 100 A/s by the hot wire chemical vapor deposition technique, has been examined by x-ray diffraction (XRD), Raman spectroscopy, H evolution, and small-angle x-ray scattering (SAXS). The films examined in this study were chosen to have roughly the same bonded H content CH as probed by infrared spectroscopy. As the film deposition rate Rd is increased from 5 to >140 A/s, we find that the short range order (from Raman), the medium range order (from XRD), and the peak position of the H evolution peak are invariant with respect to deposition rate, and exhibit structure consistent with a state-of-the-art, compact a-Si:H material deposited at low deposition rates. The only exception to this behavior is the SAXS signal, which increases by a factor of ∼100 over that for our best, low H content films deposited at ∼5 A/s. We discuss the invariance of the short and medium range order in terms of growth models available in the literature, and relate changes in th...

We present here an overview of the light scattering influence on the absorption coefficient spectra α(E) measured by constant photocurrent method (CPM) and/or by photothermal deflection spectroscopy (PDS). We compare results of numerical simulation with the measured CPM and PDS spectra and verify our theory by polishing the as-grown nanotextured layers. We show that the experimentally observed apparent absorption coefficient can overestimate the true α(E) by a factor of 10.

SnO2 thin films, is compatible with industrial requirements such as high process speed, scaling to wide substrate widths and low costs. Precise method for measuring the optical absorptance in the spectral range 300–1700 nm combines transmittance, reflectance and photothermal deflection (PDS) spectra measured on the same spot of the sample immersed in the transparent liquid with a relatively high index of refraction. The effects of the film thickness, doping gas addition and the susceptor temperature on the optical absorptance and electrical resistivity of the TCO films are assessed. We show that the doping gas concentration and the susceptor temperature influence both the incorporation ratio of dopants into SnO2 film as well as the defect concentration. The SnO2 films growth at optimum APCVD conditions have thickness 0.7 μm, average surface roughness about 40 nm, sheet electrical resistance 10 Ω/sq and the optical absorption 1% at 500 nm and about 5% at 1000 nm.

The spectral dependence of the optical absorption coefficient in thin films of hydrogenated microcrystalline silicon is measured over nine orders of magnitude in the subgap, defect-connected region, and in the above-the-band gap region. Transmittance, reflectance, and constant photocurrent method measurements are combined with Fourier-transform photocurrent spectroscopy (FTPS). Results are analyzed and interpreted as due to electron transitions from defects or interband electron transitions, all having direct relevance to the thin-film microcrystalline silicon solar cell performance. FTPS is a fast and sensitive quantitative method for quality assessment of microcrystalline silicon absorber in solar cells and can be used for quality monitoring in solar cell production.

The impact of boron doping level of nanocrystalline diamond (NCD) films on the character of cell growth (i.e., adhesion, proliferation and differentiation) is presented. Intrinsic and boron-doped NCD films were grown on Si/SiO2 substrates by microwave plasma CVD process. The boron-doped samples were grown by adding trimethylboron (TMB) to the gas mixture of methane and hydrogen. Highly resistive (0 ppm), semiconducting (133 or 1000 ppm), and metallic-like (6700 ppm) NCD films were tested as the artificial substrates for the cultivation of osteoblast-like MG 63 cells. The conductivity and surface charge increased monotonically with the increasing boron content. All NCD substrates showed good biocompatibility and stimulated the adhesion and growth of MG 63 cells. Higher osteocalcin concentration (by more than 30%) for the cells growing on 1000 and 6700 ppm boron-doped NCD films was found which indicates an enhancement in the cell growth biochemistry.

Values for the deep defect density determined from PDS, CPM or ESR may vary significantly on the same sample depending on the method of data analysis used. Experimental conditions under which they yield comparable results are discussed. Procedures for determination of deep defect density from optical spectra are reviewed and compared on samples in light-saturated states. The measurement of the absorption coefficient at E=1.2 eV, with a new range for the calibration factor, is suggested as an easy and generally usable procedure for the determination of deep defect density.

The development of μc-Si:H technology and the introduction of intrinsic μc-Si:H as photovotaically active material is retraced. Special emphasis is laid on the use of very high frequency glow discharge as a particularly propitious deposition method for μc-Si:H. Thereby, the use of a gas purifier to reduce oxygen content and obtain intrinsic layers with ‘midgap’ character is described. Recent results obtained with single-junction μc-Si:H solar cells and a-Si:H/μc-Si:H tandem solar cells are given. The analysis of carrier collection in single-junction μc-Si:H solar cells is undertaken with the variable intensity measurements method. It yields effective mobility×lifetime (μτ)eff products for the i-layer in p–i–n and n–i–p solar cells in the range 10−7–10−6 cm2 V−1. Similar values have been found for μτ-products in individual layers based on photoconductivity and ambipolar diffusion length measurements. Transmission electron microscopy images for μc-Si:H layers are given. They display a complex microstructure not suspected before. On the other hand, atomic force microscopy data reveal a pronounced surface roughness that correlates well with the optical light scattering and with the pronounced enhancement of the apparent optical absorption coefficient, in the 1–2 eV region, as already observed before.

New approach for the determination of the angular distribution of the scattered light at nano-rough surfaces/interfaces from AFM (Atomic Force Microscopy) data is presented. Calculation comes from modeling the electromagnetic field in the tight vicinity of the nano-rough surface by complex solution of Maxwell's equations and subsequent near field to far field transform. This method is demonstrated for four types of transparent conductive oxides (with rough free surfaces) deposited on glass substrates. As a result we have the amount and angular distribution of the scattered light „observed” in both transmission and reflection. Moreover calculation can be done for real sample dimensions (to compare the results with the measurement of the angular distribution function using LED laser) or for a semi-infinite sample which suppresses the interference effects and thus such distribution functions can be used as an input parameter for our 3-dimensional optical model CELL for thin film silicon solar cell modeling.In the second part of this contribution we describe our experiment of thin film silicon solar cell characterization by Light Beam Induced Current (LBIC). This measurement done for laboratory solar cell structures reveals the light scattering and light trapping properties of the multilayer stack on a glass substrate. We suggest the test structure for the direct back reflector quality comparison and thus also for its optimization.

Fourier-transform Photocurrent Spectroscopy (FTPS) was introduced four years ago [1] as a method for fast and very sensitive evaluation of the spectral dependence of the optical absorption coefficient of photoconductive thin films and recently also for the quality assessment of thin film silicon solar cells [2]. In this contribution we refer about the FTPS characterization of different thin film solar cells (amorphous silicon, microcrystalline silicon, micromorph tandem, polymer solar cells) with the main target of a fast quantum efficiency (QE) measurement. Further, we study the possibility of the FTPS-QE measurement of single cell incorporated in the solar module when only the module terminals can be used for contacting. The FTPS measurement has proved to be very fast (time scale of seconds), enabling a quick verification of quantum efficiency and subgap absorption measurement of absorber of different thin film solar cells.

CVD diamond has many outstanding physical properties. Because of its extreme hardness, this material is difficult to cut and polish and laser cutting and shaping is a technology of choice. Thick polycrystalline diamond layers were deposited by microwave plasma enhanced chemical vapor deposition on silicon substrates. After synthesis, the silicon substrate was dissolved in an acid mixture and diamond wafer has to be cut into desired shapes according to their future use. With LASAG Nd:YAG pulsed laser system KLS 246-102 we found cutting parameters for different thickness of diamond wafers from 0,1 mm to 0,7 mm. A special support with connection to vacuum was developed to keep small and light parts fixed during processing. To avoid undesirable cracks, laser scribing was used at first. Laser pulse with energy 30 mJ-200 mJ according wafer thickness and velocity 3mm.s-1-15 mm.s-1 goes two or four times along cutting lines. High temperature is the origin of black graphite layers, where absorption of laser radiation continues. Peak power contained in 0,2 ms pulse was up to 1000 W. Developed method helps to prepare CVD diamond samples of any desired shape.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this work, the effect of a diamond nucleation process on freestanding aluminium nitride (AlN)/diamond surface acoustic wave (SAW) device performances was studied. Before diamond deposition, silicon (Si) substrates have been mechanically nucleated, using an ultrasonic vibration table with submicron diamond slurry, and bias-enhanced nucleated (BEN). Freestanding diamond layers obtained on mechanically scratched Si substrates exhibit a surface roughness of R/sub MS/=13 nm, whereas very low surface roughness (as low as R/sub MS//spl les/1 nm) can be achieved on a freestanding BEN diamond layer. Propagation losses have been measured as a function of the operating frequency for the two nucleation techniques. Dispersion curves of phase velocities and electromechanical coupling coefficient (K/sup 2/) were determined experimentally and by calculation as a function of normalized thickness AlN film (kh/sub AlN/=2/spl pi/h/sub AlN///spl lambda/). Experimental results show that the propagation losses strongly depend on the nucleation technique, and that these losses are weakly increased with frequency when the BEN technique is used.

Optical absorption phenomena and in particular sub band gap absorption features are of great importance in the understanding of processes of charge generation and transport in organic pure and composite semiconductor films. To come towards this objective, an alternative and high sensitive spectroscopic approach is introduced to examine the absorption of light in pure and compound organic semiconductors. Because sub band gap absorption features are typically characterized by very low absorption coefficients, it is not possible to resolve them using common transmission and reflection measurements and high sensitive alternatives are needed. Therefore, a combination of photocurrent (Constant Photocurrent Method CPM/Fourier Transform Photocurrent Spectroscopy FT-PS) and photothermal techniques (Photothermal Deflection Spectroscopy PDS) has been used, increasing sensitivity by a factor of thousand, reaching detectable absorption coefficients ((E) down to 0.1 cm -1 . In this way, the dynamic range of measurable absorption coefficients is increased by several orders of magnitude compared to transmission/reflection measurements. These techniques have been used here to characterize ground state absorption of thin films of MDMO-PPV, PCBM and a mixture of both materials in a 1:4 ratio, as typically used in a standard active layer in a fully organic solar cell. The spectra reveal defect related absorption phenomena and significant indication of existing interaction in the ground state between both materials, contrary to the widely spread conviction that this is not the case. Experimental details of the techniques and measurement procedures are explained.

In this work, the effect of diamond nucleation process on freestanding AlN/diamond SAW device performances was studied. Before diamond deposition, silicon substrate were mechanically nucleated, using an ultrasonic vibration table with sub-micron diamond slurry, and bias enhanced nucleated (BEN). Freestanding diamond layers obtained on mechanically scratched Si substrates exhibit a surface roughness of R/sub MS/=13nm whereas very low surface roughness (as low as R/sub MS//spl les/1 nm) can be achieved on BEN diamond layer. Propagation losses (/spl alpha/) and electromechanical coupling coefficient (K/sup 2/) have been measured as a function of the operating frequency and the normalized AlN film thickness (kh/sub AlN/=2/spl pi/h/sub AlN///spl lambda/). Experimental results show that the propagation losses strongly depend on nucleation technique while the electromechanical coupling coefficient slightly depends on nucleation technique.

Influence of front TCO thickness, surface texture and different back reflectors on short-circuit current density and fill factor of thin film silicon solar cells were investigated. For the front TCO studies, we used ZnO layers of different thickness and applied wet chemical etching in diluted HCl. This approach allowed us to adjust ZnO texture and thickness almost independently. Additionally, we used optical modeling to calculate optical absorption losses in every layer. Results show that texture and thickness reduction of front ZnO increase quantum efficiency over the whole spectral range. The major gain is in the red/IR region. However, the higher sheet resistance of the thin ZnO causes a reduction in fill factor. In the back reflector studies, we compared four different back reflectors: ZnO/Ag, Ag, ZnO/Al and Al. ZnO/Ag yielded the best, Al the worst light trapping properties. Furthermore, the Ag back contact turned out to be superior to ZnO/Al for microcrystalline cells. Finally, the smooth ZnO/Ag back contact showed a higher reflectivity than the rough one. We prepared pin cells with rough and smooth ZnO/Ag interface, leaving the roughness of all other interfaces unchanged.

Absorption losses at a nanorough silver back reflector of a solar cell were measured with high accuracy by photothermal deflection spectroscopy. Roughness was characterized by atomic force microscopy. The observed increase of absorption, compared to the smooth silver, was explained by the surface plasmon absorption. Two series of silver back reflectors (one covered with thin ZnO layer) were investigated and their absorption related to surface morphology. (C) 2004 American Institute of Physics.

The authors present progress in the three regions important for optimization of the highest long term a-Si:H solar cells efficiency: (1) in order to achieve light saturated state rapidly and controllably a new method of the accelerated degradation by combined AM1 and pulsed ruby laser illumination is proposed; (2) diagnostic of the degraded state is then made possible by a new constant photocurrent method setup combining standard and transmission modes which gives absorption coefficient a in the absolute units and undisturbed by interferences; (3) the possibility to measure deep defect density of states directly on a-Si:H solar cells by space-charge-limited-current time-of-flight is demonstrated.

Optical spectra of semiconductor provide a fundamental source of information on its electronic structure. Photons can excite electrons from the filled valence bands to the empty conduction bands (interband optical transitions), from filled defect states to the conduction band or from the valence band to the empty defect states (defect-connected optical transitions). These are the basic optical transitions, which we will treat here.

We measure subgap absorption on n-type amorphous silicon using the “absolute” constant photocurrent method. We find that for typical monochromator probe beam intensities the measurement is not significantly influenced by lifetime changes. When the measurement is performed under light bias, an apparent increase in the defect absorption coefficient is observed, but no change in the photoexcitation threshold or spectral shape of the absorption band is seen. We show that this increase is likely due to a bias-light amplification of spectrally dependent lifetime changes. Our measurements suggest a larger electron capture cross section of positive valence band tail states compared to neutral dangling bonds.

We report on the experimental realization of amorphous/microcrystalline silicon tandem solar cells (Micromorph) based on our three-dimensional design. An enhancement is reached in the short-circuit current by 40%, with an excellent open-circuit voltage of 1.41V and a fill factor of 72%. We have used nanoholes or microholes dry etched into the ZnO front contact layer. Monte Carlo optical modeling shows that stable efficiency of amorphous silicon p-i-n solar cells in over 12% range is possible. For the Micromorph cells, efficiency over 15% with the thickness of amorphous Si below 200 nm and of microcrystalline Si around 500 nm is possible.

High performance transparent conducting oxides (TCOs), have significance for optimising PV performance. We have developed an advanced atmospheric pressure chemical vapour deposition process, by applying fast experimentation and using a combinatorial chemistry approach to aid the studies. The deposited films were characterised for crystallinity, morphology (roughness), haze and resistivity to aid optimisation of material suitable for solar cells. Optical measurements on these samples showed low absorption losses, less than 1% around 500 nm for one pass, which is much lower than those of industrially available TCOs. Selected samples were then used in manufacture of single junction a-Si : H solar cells, which showed high initial solar energy conversion efficiencies up to 9.3% and high short circuit current densities of 15 mA/cm². Compared with (commercially available) TCO CVD coated glasses, these TCO coatings show excellent performance resulting in a high quantum efficiency yield for a-Si : H solar cells.

Constant photocurrent (CPM) and steady state photograting (SSPG) measurements have been performed on a series of hot wire (HW) and glow discharge (GD) hydrogenated amorphous silicon (a‐Si:H) films, where the substrate temperature was varied in each case to affect the bonded H content. A reduction in the magnitude of the Staebler‐Wronski effect, as observed by CPM after saturation light soaking, is seen when the H content is reduced in both sets of samples, but the lowest saturated CPM values and the highest SSPG diffusion lengths measured after saturation occur for HW films having H contents in the range 1‐4 at.%. Although correlations exist between the number of excess defects produced by saturation light soaking and microscopic parameters such as the H content and the optical bandgap, there is not a simple correspondece for both sets of samples. This suggests that the Staebler‐Wronski saturation may be influenced in part by the film microstructure.

This paper describes the use, within p–i–n- and n–i–p-type solar cells, of hydrogenated amorphous silicon (a-Si:H) and hydrogenated microcrystalline silicon (μc-Si:H) thin films (layers), both deposited at low temperatures (200°C) by plasma-assisted chemical vapour deposition (PECVD), from a mixture of silane and hydrogen. Optical and electrical properties of the i-layers are described. These properties are linked to the microstructure and hence to the i-layer deposition rate, that in turn, affects throughput in production. The importance of contact and reflection layers in achieving low electrical and optical losses is explained, particularly for the superstrate case. Especially the required properties for the transparent conductive oxide (TCO) need to be well balanced in order to provide, at the same time, for high electrical conductivity (preferably by high electron mobility), low optical absorption and surface texture (for low optical losses and pronounced light trapping). Single-junction amorphous and microcrystalline p–i–n-type solar cells, as fabricated so far, are compared in their key parameters (Jsc, FF, Voc) with the [theoretical] limiting values. Tandem and multijunction cells are introduced; the μc-Si: H/a-Si: H or [micromorph] tandem solar cell concept is explained in detail, and recent results obtained here are listed and commented. Factors governing the mass-production of thin-film silicon modules are determined both by inherent technical reasons, described in detail, and by economic considerations. The cumulative effect of these factors results in distinct efficiency reductions from values of record laboratory cells to statistical averages of production modules. Finally, applications of thin-film silicon PV modules, especially in building-integrated PV (BIPV) are shown. In this context, the energy yields of thin-film silicon modules emerge as a valuable gauge for module performance, and compare very favourably with those of other PV technologies. Copyright © 2004 John Wiley & Sons, Ltd.

Undoped hydrogenated microcrystalline silicon (νc-Si:H) layers and solar cells have been deposited by plasma-enhanced chemical vapour at low temperature and at different values of VHF plasma power and silane to hydrogen dilution ratios. Transport and defect density measurements on layers suggest that structural properties (e.g. crystallite shape and size) only marginally influence the electronic transport properties. The latter are influenced strongly by the Fermi level, which depends on the oxygen impurity content. Furthermore, they are best described by the quality parameter ν0τ0 (deduced from photoconductivity and ambipolar diffusion length). Cell efficiency correlates better with νoτ0 than with the defect density as determined from subbandgap absorption. Anisotropy of the transport properties in some νc-Si:H is also demonstrated but does not seem to play a major role in νc-Si:H cells deposited at high rates under VHF glow discharge conditions.