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Sb2Se3 has emerged as an important photoelectrochemical (PEC) and photovoltaic (PV) material due to its rapid rise in photoconversion efficiencies. However, despite its binary nature, Sb2Se3 has a complex defect chemistry, which reduces the maximum photovoltage that can be obtained. Thus, it is important to understand these defects and to develop passivation strategies in order to further improve this material. In this work, a comprehensive investigation of the charge carrier dynamics of Sb2Se3 and the influence of sulfur treatment on its optoelectronic properties was performed using time resolved microwave conductivity (TRMC), photoluminescence (PL) spectroscopy and low frequency Raman spectroscopy (LFRS). The key finding in this work is that upon sulfur treatment of Sb2Se3, the carrier lifetime is increased by the passivation of deep defects in Sb2Se3 in both the surface region and the bulk, which is evidenced by increased charge carrier lifetime of TRMC decay dynamics, increased radiative recombination efficiency and decreased deep defect level emission (PL), and improved long-range order in the material (LFRS). These findings provide crucial insights into the defect passivation mechanisms in Sb2Se3 paving the way for developing highly efficient PEC and PV devices.

Sb2Se3 has emerged as an important photoelectrochemical PEC and photovoltaic PV material due to its rapid rise in photoconversion efficiencies. However, Sb2Se3 has a complex defect chemistry, which reduces the maximum photovoltage. Thus, it is important to understand these defects and develop defect passivation strategies in Sb2Se3. A comprehensive investigation of the charge carrier dynamics of Sb2Se3 and the influence of sulfur treatment on its optoelectronic properties is performed using time resolved microwave conductivity TRMC , photoluminescence PL spectroscopy, and low frequency Raman spectroscopy LFR . The key finding in this work is that upon sulfur treatment of Sb2Se3, the carrier lifetime is increased by the passivation of deep defects in Sb2Se3 in both the surface region and the bulk, which is evidenced by increased charge carrier lifetime of TRMC decay dynamics, increased radiative recombination efficiency, decreased deep defect level emission PL , and the emergence of new vibration modes by LFR

In this paper, contactless transient photo-conductance measurements are applied to p-doped mono-crystalline Silicon (p-Si) coated by two different kinds of aluminum oxide (Al2O3) layers in order to study alternative routes to the standard atomic layer deposition (ALD). The aluminum oxides layers were deposited by either spin coating or ion layer gas reaction (ILGAR?). For both coatings an increase of the charge carrier life time is observed indicating a passivation of the p-Si surface. This study shows alternative deposition methods and the potential of transient photocon- ductance measurements for the elucidation of the origin of the passivation. We show that the passivation induced by coating deposited via ILGAR is at least partially due to charge carrier trapping and storage at the interface. It was also surprisingly found that for those coatings, annealing at 425℃ leads to a decrease of the life time. This points to temperature instability for both coatings.

The influence of different redox mediators and electrolyte constituents on charge transfer processes in dye-sensitized solar cells (DSC) was studied by contactless transient photoconductance (TPC) measurements. Device subsets without FTO (Fluorine-doped tin oxide) contacts were prepared to increase the reliability and sensitivity of the TPC measurements. Results revealed a decrease of electron decay rate with increasing concentration of the redox couple ([Co(III/II)(bpy)3](PF6)3/2) which was attributed to an improvement of the reduction of the dye cation (dye regeneration). Furthermore, the presence of the electrolyte additives 4-tert-butylpyridine (TBP) and chenodeoxycholic acid was found to decrease the electron decay rate, which was attributed to blocking of interfacial charge recombination. The use of other redox couples (quinone/hydroquinone and ferrocene/ferrocenium) with these electrolyte additives displayed a significant improvement for ferrocene/ferrocenium, while the electron lifetime for quinon...

Lead halide perovskites have recently been used as light absorbers in hybrid organic–inorganic solid-state solar cells, with efficiencies as high as 15% and open-circuit voltages of 1 V. However, a detailed explanation of the mechanisms of operation within this photovoltaic system is still lacking. Here, we investigate the photoinduced charge transfer processes at the surface of the perovskite using time-resolved techniques. Transient laser spectroscopy and microwave photoconductivity measurements were applied to TiO2 and Al2O3 mesoporous films impregnated with CH3NH3PbI3 perovskite and the organic hole-transporting material spiro-OMeTAD. We show that primary charge separation occurs at both junctions, with TiO2 and the hole-transporting material, simultaneously, with ultrafast electron and hole injection taking place from the photoexcited perovskite over similar timescales. Charge recombination is shown to be significantly slower on TiO2 than on Al2O3 films.

Manganese oxide films on conductive substrates were prepared by electrochemical deposition. Charge carrier kinetics in these films was studied by contactless transient photoconductivity measurements. These measurements revealed the generation of mobile charge carriers with a nonneglectable lifetime. The transport from charge carriers generated in the oxides to the substrate was observed.

The surface of commercial TiO2 compounds (P25 and ST01) has been modified with Ag nanoparticles induced by radiolysis. On P25, the Ag nanoclusters are very small (1–2 nm) and homogeneous in size while on ST01, two populations of nanoparticles are obtained, small nanoparticles (1–2 nm) and larger ones (mean diameter 7 to 12 nm depending on the silver loading). The photocatalytic properties of Ag-modified TiO2 have been studied for phenol photodegradation in aqueous suspensions under UV and visible light. Their electronic properties have been studied by time resolved microwave conductivity (TRMC) to follow the charge-carrier dynamics. TRMC measurements show that the TiO2 modification (P25 and ST01) with Ag nanoparticles plays a role in charge-carrier separations increasing the activity under UV light. Indeed, Ag nanoparticles act as electron scavengers, decreasing the charge carrier recombination. TRMC measurements show also that more electrons are produced in the conduction band of P25 under UV illuminatio...

The kinetics of charge carriers in ZnO films and nanorods was analyzed by contactless transient photoconductance (TPC) measurements. The use of two excitation wavelengths allowed to identify the decay processes. The TPC signal displayed a significantly accelerated decay in ZnO films after sensitization with a ruthenium bipyridyl dye which was attributed to a higher electron–hole recombination whereas the electron–dye cation recombination was relatively slow. ZnO nanorods displayed no such destructive influence of the dye adsorption. Recombination processes took place over a large time range because of the heterogeneity of the samples.

A quasi-solid-state dye-sensitized solar cell is presented, where an electrolyte film replaces the conventional liquid electrolyte, reaching a solar light-to-current conversion efficiency of 3%. This proves the importance of surface conduction of the positive charge, e.g., via the Grotthuss mechanism. Contactless transient photoconductance measurements were performed on operating cells, revealing decay behavior of photoinduced charge carriers, dependent on external applied potential conditions. The measurements show that the decay is controlled by the injection of electrons into the front contact, hindered or enhanced by the field in the space charge region. Furthermore, the influence of redox molecules on the decay of photogenerated charge carriers in sensitized TiO2 films was analyzed and found to be dependent on the redox pair concentration. We ascribe this effect to the regeneration of the oxidized dye by iodide, in this way screening the positive charge from possible recombination with injected elect...

Surface charge, surface state density and interface recombination behavior on polished float zone (FZ) solar cell substrates were investigated after various wet-chemical pre-cleaning procedures and deposition of amorphous silicon (a-Si:H) or silicon nitride (a-SiNx:H). Applying surface photo voltage (SPV), microwave detected photo conductance decay (µW-PCD) and transient microwave conduction (TRMC) measurements, electronic interface properties were monitored repeatedly during the preparation processes. As shown for an inverted a-Si:H/c-Si hetero-junction structure, with front side passivation by a-SiNx:H and a p-type a-Si:H emitter on the rear side, the effect of optimised wet-chemical pre-treatment can be preserved during the subsequent soft plasma enhanced chemical vapour deposition of a-Si:H or a-SiNx:H. This leads to hetero-interfaces with low interface recombination velocities. These results were compared to previously reported findings, obtained on textured Czochralski (CZ) single crystalline substrates. a-SiNx:H is known to result in a field effect passivation. Nevertheless a strong influence of wet-chemical treatments on surface charge and recombination losses was observed on both flat and textured a-SiNx:H/c-Si interfaces. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High-temperature contact firing of screen printable metal pastes is getting more problematic as silicon wafers used in solar cell production are becoming thinner. Besides, an electronic degradation of the Si x N y /c-Si interface occurs at these temperatures especially if the Si x N y layer is directly deposited onto high-quality absorbers as on the front side of a-Si:H/c-Si hetero-contact solar cells of inverted geometry. The latter structure has been proposed as an easy producible high-efficiency solar cell. Low-temperature alternatives such as local ablation of Si x N y with 355 nm laser radiation are examined with regard to the stability of the electronic quality of passivated areas between the openings in the Si x N y layer. Contactless time-resolved microwave conductivity measurements (TRMC) are applied to measure changes in electronic passivation after these treatments. Subsequent galvanic metallization of the openings is optimized for its use as ohmic contacts.

Standard crystalline silicon homojunction solar cells have been irradiated with high energy protons at variable energies between 0.8 MeV and 65 MeV. As one possible criterion for the evaluation of the radiation induced degradation, we compared the suppression of the bandgap electroluminescence at a wavelength around 1150 nm for the solar cells, irradiated at different energies. The lowest electroluminescence efficiency has been observed for an intermediate proton energy of 1.7 MeV. At this energy value, however, crystalline silicon solar cells are not homogeneously damaged, as shown by the defect profiles, calculated by the SRIM code. We propose therefore a irradiation at a higher energy in order to obtain a relative homogeneous defect profile. At 65 MeV the projected range of the protons in silicon is about 2 cm and we obtain a nearly constant defect distribution in the solar cell and the irradiation can be performed in air. Subsequently we compared the fluence dependence of the degradation of the solar cell parameters after 65 MeV irradiation with other material parameters, such as effective diffusion lengths, as calculated by the quantum yield spectra and the effective excess charge carrier lifetime, as measured on silicon wafers by the contactless TRMC-technique. Similar degradation has been found for the short circuit current, solar cell efficiency and electroluminescence efficiency and a good agreement between diffusion length and excess charge carrier lifetime changes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Semiconductor (photo)electrochemical knowledge is mostly based on potential dependent (photo)current measurements, on electrons turned over by the semiconductor electrode. Photo or potential induced microwave reflection measurements can provide information on the potential dependent dynamics of electronic charge carriers within the semiconductor electrode. This contribution shows that information gained by both types of measurements, current and microwave reflection, is consistent and, together, yield a more complete and detailed picture of semiconductor electrochemical mechanisms. Most of the measurements present so far in the literature with this combined technique are on the silicon–electrolyte interface. In this paper, the good agreement of theory and experiment is demonstrated at layered semiconductors like molybdenum disulfide or tungsten diselenide which promise favourable properties for thin film solar applications. Besides analysing p- and n-type samples with respect to surface recombination and (photo)corrosion, a quantitative determination of interfacial rate constants for a minority charge carrier exchange via the semiconductor–electrolyte interface is presented. By exemplary qualitative and quantitative measurements the potential of this combined technique is discussed and the behaviour of charge carriers in layered semiconductors studied and interpreted.

Excess charge carrier transport and relaxation in semiconductor layered structures have been numerically simulated by a finite-difference method.

A new structure to circumvent the problem of light absorption in dead layers (i.e., highly doped emitters) is investigated: an inversion of the conventional a-S:H/c-Si solar cell hetero-structure, i.e., illumination of the backside, the c-Si part of the junction. This has the advantage that only a small part of the excitation light reaches the a-Si:H emitter. However, in the simplest configuration the lateral collection of excess majority carriers is less easy and a higher series resistance therefore limits the current. The longer path of excess-charge carrier pairs to the junction also causes higher demands on the minority carrier lifetime than in the conventional configuration. It will be shown that a thin (70 nm) Si 3 N 4 film offers an efficient electrical passivation as an antireflective coating. The first inverted Si 3 N 4 /n c-Si/p a-Si:H solar cells were characterized by a moderate efficiency of about 11%. Most detrimental appeared to be the high series resistance of the device. Modelling enabled the causes of this effect to be localized and new ways of contacting the c-Si base decreasing the series resistance will be proposed. Also the contacting of the c-Si part of the junction will be discussed in view of an optimal absorption of the incident radiation.

Transparent, conductive SnO 2 (FTO) films and colloidal TiO 2 films deposited on these FTO films are investigated by means of contactless transient photoconductance measurements in the microwave frequency range (TRMC measurements). For the bare FTO–glass films excitation with 355 nm light pulses leads to appreciable TRMC signals indicating the semiconductor properties of the material. For TiO 2 films on FTO–glass films, injection of excess electrons from TiO 2 into FTO is observed.

Microwave conductivity and two channels of recombination process were observed in the CuI films. Spin orbital splitting resulted in split in the valence band of CuI. The dye molecules attached to the CuI film act as an electron mediator in addition to the sensitization process under back wall-mode illumination.

Microwave Hall experiments in a bimodal cavity are presented. The principle of the measurements is elucidated and the experimental set-up is considered. A quantitative evaluation of the measurement data is given. Precise cavity tuning with the help of a rotating sample holder is discussed. Results of measurements on crystalline silicon and pyrite (FeS 2 ) are shown.

p-type Si wafers provided with silicon nitride films at the surface are investigated by contactless transient photoconductivity measurements. Comparing wafers of different resistivities and wafers at one side and at two sides provided with nitride films shows that separation and storage of excess charge carriers in the space charge region is the main kinetic process at low injection level. Fitting of the experimental data with a simple model leads to the conclusion that the electron mobility in the interface is strongly reduced, a value 250(−+20%) cm2 V−1 s−1 is determined, independent of the wafer resistivity. This confirms the reduction of the electron mobility reported in the literature on the basis of completely different measurements.

The use of microwave photoconductivity measurements as a tool for the non-destructive characterization of semiconductors is studied and the experimental equipment is described. Through some examples of experiments on silicon wafers covered with a silicon nitride coating the merits of different ways to perform these measurements are discussed.

Amorphous silicon/crystalline silicon (c-Si) heterojunctions are studied by contactless transient photoconductivity measurements at the microwave frequency range. Excellent passivation of the n-type crystalline silicon (n c-Si) surface by n-type, hydrogenated amorphous silicon (n a-Si:H) films is observed. The influence of band offsets is discussed. It is shown that energy converting junctions can be characterized accurately by these measurements. Charge carrier kinetics in the junctions are controlled by charge carrier separation determined by band bending and by interface recombination.

The optoelectronic properties of μc-Si films produced in different ways are studied by contactless transient photoconductivity measurements in the microwave frequency range. A strong charge carrier trapping is observed in most μc-Si films. The effective mobility determined from these measurements appears to be an appropriate parameter to characterize these films. The films show a high absorption at 1064 nm, tentatively attributed mainly to defect absorption.

It is shown by contactless transient photoconductivity measurements in the microwave frequency range that Si3N4 films are an outstanding passivation of the n-type c-Si surface. Si3N4 on n-type Si forms an accumulation layer, which acts as an ideally reflecting potential barrier for minority carriers (holes). Due to the small space charge layer capacitance, minority carrier storage at this interface is very limited. In contrast to the latter measurements on p-type Si wafers covered with Si3N4 are characterized by storage of excess charge carriers in the surface depletion layer. The stored charge carriers decay slowly. The minority carriers (electrons) collected at the surface show a reduced mobility.

The silicon/silicon nitride interface was studied by contactless photoconductivity measurements in the microwave frequency range. Good passivation and antireflection properties of Si 3 N 4 coatings were observed. It is shown that spatially resolved measurements offer a very sensitive tool for the characterization of the lateral thickness distribution of the Si 3 N 4 film. The inversion layer at the p c-Si/Si 3 N 4 interface causes a storage of excess charge carriers that can be observed by time resolved photoconductivity measurements.

The optoelectronic properties of microcrystalline silicon (μc-Si) films were determined by contactless transient photoconductivity measurements in the microwave frequency range. High mobilities were observed in μc-Si produced by laser annealing although the material contains impurities diffused from the substrate and is doped. Hot wire and plasma enhanced chemical vapor deposited (PECVD) μc-Si films are characterized in the best case by mobilities in the order of magnitude of the mobility in a-Si:H.

The passivating influence of a-Si:H films on the c-Si surface is shown by contactless transient photoconductivity measurements in the microwave frequency range. A relation between the signal and the performance of a-Si:H/c-Si heterojunctions for solar energy conversion was found. The injection of excess charge carriers from the a-Si:H film into the c-Si substrate was observed and shown to yield information on charge carrier transport in the a-Si:H film and in the space charge region.

The influence of doping on the (opto)electronic properties of a-Si : H films is investigated by transient photoconductivity and photo-induced absorption measurements. The decay rate of the majority charge carrier decreases with doping due to fast minority carrier trapping already active at low doping levels. The transition from electron to hole conduction is observed at 3 ppm B2H6. At high doping levels the recombination rate becomes faster by recombination via doping-induced defects.

To investigate the relation between interface passivation and the performance of an a-Si:H/c-Si solar cell, we monitored the glow discharge deposition process of n-doped a-Si:H films on p-doped crystalline silicon in situ by transient photoconductivity measurements in the microwave frequency range (TRMC measurements). After the end of the deposition process, we also performed ex situ TRMC measurements of the heterojunctions. From three representative samples, we prepared solar cells and their performances were compared to the TRMC measurements.

a-Si:H/c-Si junctions were investigated by contactless photoconductivity measurements in the microwave frequency range. The dependence of the junction properties on the thickness of the a-Si:H films was determined via a characterization by the interface recombination velocity at the junction at a fixed injection level. It is shown that the differential recombination rate at the junction as a function of the injection level yields information on band bending and interface defect density. The separation and collection of excess charge carriers at the junction was observed with time-resolved measurements.

Contactless transient photoconductivity measurements in n-doped GaAs films with different doping concentrations are presented. It is shown that at low excess carrier densities the signal is due to excess charge carriers separated in the space charge region. These signals are characterized by a long decay time not related to the bulk properties of the films. At moderate excess carrier densities surface recombination takes place still hampered by the space charge field giving way to a high surface recombination at high excitation densities.

The photogeneration of charge carriers in poly[methyl(phenyl)silylene] (PMPSi) is a multistage process including, photoinduced electron transfer and relaxation of the charge-transfer state which results in ion (polaron) pair formation. The radical ions are usually detected by transient optical absorption. Covalently linked molecular dipoles or Coulomb-correlated ion-pairs, and free and shallow localized carriers can also be detected by the method of time-resolved microwave conductivity (TRMC). This method is based on the proportionality of the relative change in the reflected microwave power and the “induced conductivity” due to dipolar transitions that are caused by the absorption of a light. The formation of radical ion-pairs in poly[methyl(phenyl)silylene] upon light excitation was studied by the abovementioned techniques.

A model simulating excess charge carrier kinetics in Si wafers was developed taking into account space charge fields and surface recombination. This model was applied to experimental data obtained by contactless transient and frequency resolved photoconductivity measurements of silicon wafers with accumulation or depletion layers at the surface. It is shown that a surface accumulation layer has only a minor influence and surface recombination can be analyzed with a surface recombination velocity weakly depending on the excess carrier concentration. At low injection level a surface depletion layer leads to a strongly nonlinear behavior of the photoconductivity due to excess charge carriers stored in the space charge region. The presence of these charge carriers is also revealed by the tail of the transient photoconductivity signal characterized by a decay time longer than the volume lifetime. At higher injection level the contribution of these charge carriers to the photoconductivity can be neglected and t...

The decay of optically generated excess charge carriers at the heterointerface between crystalline silicon and amorphous silicon has been monitored in situ during plasma deposition of the amorphous layer. A dramatic increase in the interface recombination rate is seen instantly when the silane plasma is ignited. In a later stage of amorphous layer deposition, the recombination rate decreases. This interface passivation depends strongly on the substrate temperature and is more efficient at higher temperature and in the presence of silane plasma. The effect is not due to a change in the band bending at the heterointerface.

The damage induced by hydrogen and helium plasmas at the surface of crystalline silicon has been monitored in situ by time‐resolved microwave conductivity and by spectroscopic ellipsometry measurements. Both plasma treatments increase the decay rate of the optically generated excess charge carriers and decrease the amplitude of the microwave reflection transients. While for the helium plasma a high density of electronic defects is created immediately after plasma ignition, a continuously increasing number of recombination centers is observed in the case of the hydrogen plasma exposure. In support of the transient microwave measurements, the analysis of the spectroscopic ellipsometry measurements reveals the creation of a damaged surface layer, which in the case of the helium plasma exposure has a high and in the case of the hydrogen plasma a low fraction of amorphous silicon. This can be explained by the different nature of the processes involved in the interaction of hydrogen (chemical) and helium (physi...

Theory and measurements of the conductivity and the (transient) photoconductivity in the microwave frequency range are presented. The theory is tested on noninvasive measurements of semiconductors with known properties, i.e., Si wafers, in a simple apparatus. Quantitative agreement between theory and experiment is found without the use of adjustable parameters. A contactless and accurate determination of the conductivity of Si wafers in a restricted conductivity range is proposed. The quantitative evaluation of photoconductivity measurements makes a detailed discussion of nonuniform photoconductivity possible. The requirements for reliable measurements of nonhomogeneous charge carrier kinetics are discussed.

Multilayers of a-Si:N/a-SiN:H and a-Si:H/a-SiC:H were investigated by contactless transient photoconductivity measurements. A faster decay of the photoconductivity was observed in the a-Si:H/a-SiC:H multilayer whereas the a-Si:H/a-SiN:H multilayer was characterized by a slower decay relative to a pure a-Si:H film. These effects are ascribed to defects associated with interface states. The electron mobility in the thin a-Si:H layers of the multilayers does not appear to be appreciably different from that in pure a-Si:H films.

Experimental results of contactless time-resolved photoconductivity measurements in intrinsic a-Si:H films are compared to numerically simulated results with an electron-hole recombination as the main decay channel. This simplistic model is extended stepwise by incorporating experimental features of increasing complexity in order to fit the experimental results. It appears possible to explain the experimental data by a model containing only one free parameter. This leads to the proposal of a value for the rate constant for the recombination of electrons and holes by a second-order reaction of 1.0 × 10 −9 cm 3 s −1 as a satisfactory fit to the data.

During removal of amorphous silicon films deposited on crystalline silicon substrates by dry etching in a hydrogen plasma the kinetics of mobile excess charge carriers have been followed by measuring the change of the microwave reflection after laser pulse illumination. Following the amplitude of the measured transient signals the thickness of the remaining amorphous silicon film can be determined and the decay in the nanosecond time range yields information about the defect density of the substrate surface. The impact of the plasma process on the surface recombination is shown and a criterion for endpoint detection is given in the case of a‐Si:H removal from crystalline silicon covered with a SiO2 layer.

A qualitative correlation between time resolved microwave conductivity (TRMC) and the quality of a-Si:H films is discussed. Aim of this work is to find a more quantitative correlation between TRMC signal features and proposed kinetic mechanisms in a-Si:H. Initial results concerning electron-hole recombination reactions are presented and discussed.

The recombination at high excess charge concentrations (higher than 10 18 cm −3 ) in a-Si:H has been studied by comparison of the excess electron concentration obtained by contactless transient photoconductivity measurements with numerical calculations. The first stage of the recombination process is described satisfactorily by a recombination between mobile excess electrons and all excess holes. In later stages this simple model predicts a too high recombination rate. A better description has been obtained if the recombination rate parameter depends on the energy of the hole.

A quasi-solid-state dye-sensitized solar cell is presented, where the conventional liquid electrolyte is replaced by an electrolyte film, reaching a solar light-to-current conversion efficiency of 3%. Contactless transient photoconductance measurements were performed, revealing decay behavior of photoinduced charge carriers, dependent on external applied potential conditions. The measurements show that the decay is controlled by the injection of electrons into the front contact, hindered or enhanced by the field in the space charge region.

Contactless in-situ measurements of the microwave detected transient photoconductivity during growth of intrinsic a-Si:H films by plasma enhanced chemical vapour deposition are presented. It is shown, that these measurements can be performed without perturbation of the deposition process. The growth of a-Si:H films at 250° C and 120° C substrate temperature is studied and the information obtained from these measurements is discussed. In-situ characterization during growth of a multilayer structure with films deposited subsequently at 120° C, 250° C and again at 120° C is shown.

Relaxing in the sunlight. Long time-transient decays of photogenerated carriers in P3HT:PCBM blends for organic solar cells are interpreted in terms of the relaxation of hole carriers in a broad density of states. The after-pulse time-resolved microwave conductivity (TRMC) decays observed in P3HT:PCBM blends display a dependence on time close to t−β, independent of excitation intensity, in the 10 ns–1 μs range. This is explained in terms of the relaxation of carriers in a Gaussian density of states (DOS). The model is based on a demarcation level that moves with time by thermal release and retrapping of initially trapped carriers. The model shows that when the disorder is large the after-pulse decay of the type t−β is obtained, while at low disorder and large temperature the carrier distribution becomes independent of time. In the measurements different β values were observed depending on the solvent used for spin-coating: 0.4–0.6 for chlorobenzene and 0.3–0.4 for toluene. The model was applied to extract the shape of the DOS from the TRMC decays, giving a dispersion parameter of about 120 meV for blends with high P3HT content.

The monitoring of the microwave reflection changes after pulsed laser illumination enables the in‐situ characterization of important optical and electrical material parameters during the growth of intrinsic hydrogenated amorphous silicon on low conductivity substrates.

The optoelectronic properties of a-Si:H films grown at different substrate temperatures between 30°C and 250°C were evaluated in-situ by contactless Time Resolved Microwave Conductivity (TRMC) measurements. The transient photoconductivity induced by 532nm laser pulses during the growth of multilayer systems composed of a-Si:H layers deposited at different temperatures made a direct comparison of these films possible. The maximum height of the TRMC signal was observed to decrease strongly with decreasing deposition temperature. Additionally, the annealing of layers deposited at low temperatures was studied by TRMC, stationary photoconductivity, IR and ESR measurements. Whereas a considerable increase of the photoconductivity and the TRMC signal and a decrease in the spin density was observed during annealing at 250°C, the IR transmission spectra remained unchanged.

Three commercial TiO2 compounds (Degussa P25, Sachtleben UV100, and Millenium PC50) and their platinized forms have been studied by the time-resolved microwave conductivity (TRMC) method to follow their charge-carrier dynamics and to relate it to the photocatalytic activity for phenol degradation in TiO2 aqueous suspensions. The degradation reaction has been studied in detail, following the time evolution of the concentration of phenol and its intermediates by liquid chromatography. The results show that platinization has a distinct influence on the commercial compounds, decreasing globally the activity of P25 and increasing the activity of PC50 and UV100. An influence of charge-carrier lifetimes on the photoactivity of pure and platinized TiO2 samples has been evidenced.

We have synthesized new carbazole and ethylenedioxythiophene based molecular glasses with hydrazone and imine goups. Thermal analysis confirms the metastable amorphous properties of these molecules with glass temperature in the range of 62 to 76 °C. Electrochemical properties have been studied and show the effect of the conjugated imine or hydrazone groups on the electronic delocalization of the structures. A decrease of the oxidation potential, compared to the parent unsubstituted molecules, is observed, which decreases the HOMO energetic level and improves the donor properties of the molecules. Amorphous materials of low molecular weight should allow the regeneration of the oxidized sensitizer in agreemen t with their respective energetic levels. Moreover, all the molecules absorb light in the range of th e wavelength, blue-shifted in comparison with the ruthenium dye, which limits the shield effect for a good photogeneration of charge carrier in the dye. Results suggest that such molecular glasses could find applications in photovoltaic devices.

Laser crystallization of a-Si:H on PES, PET and AryLite™ polymer substrates is reported. For each material, the glass transition temperature T g and the coefficient of thermal expansion have been evaluated, to determine the optimum deposition and crystallization processes conditions. 1000-A thick intrinsic amorphous silicon films have been deposited on the substrates by Plasma Enhanced Chemical Vapour Deposition in the temperature range of 120–250°C. Dehydrogenation and crystallization have been obtained by high energy (10 J) XeCl pulsed excimer laser. The irradiation conditions have been varied to study their influence on the electrical and optical properties of crystallized material. Structural characterization has been performed by X-ray Diffraction. Increasing the radiation energy densities up to 220 mJ/cm 2 crystallites sizes up to 750 A have been obtained.

The characterization of III–V semiconductor films by contactless and non-invasive conductance and transient photoconductance measurements in the microwave frequency range were investigated. It was shown that the conductivity (of a GaSb film) and the majority carrier mobility (of GaAs and InP films) can be determined. Besides, information on charge carrier transport, in particular at the surface is obtained.