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The hydrogen concentration in hydrogenated amorphous silicon (a-Si:H), produced by plasma-enhanced chemical vapor deposition, was measured by Raman and Fourier transform infrared spectroscopy before and after thermal annealing. The possibility of Raman spectroscopy to perform depth dependent analysis in adapting the analysis wavelength is used. The findings presented in this paper are supported by secondary ion mass Spectrometry depth profiles. Moreover, we show that Raman spectroscopy can be used to get depth-dependent information about the microstructure and the influence of annealing on the microstructure of a-Si:H.

Industry has previously established a 10% stable total module efficiency 1.1 × 1.3 m2 thin film silicon tandem junction (TJ) module manufacturing baseline. A similar silicon TJ cell manufacturing process has been established, using a plasma enhanced chemical vapor deposition (PECVD) tool with an excitation frequency of 13.56 MHz, which was modified to handle 30 × 30 cm2 substrates. Extensive PECVD process window characterization was undertaken for the silicon layers that have the biggest impact on device performance. Single layer silicon on glass data and 1 × 1 cm2 single junction and TJ solar cell data for amorphous intrinsic silicon and microcrystalline intrinsic silicon layers have been collected. Single layer characterization data for p-doped microcrystalline silicon oxide layer (μc-SiOx:H-p) for aluminum doped zinc oxide substrates is being presented, as well as solar cell data. The manufacturability of the μc-SiOx:H-p process is being considered. Finally, we present the best solar cell results obtained with the optimized PECVD process, as well as baseline performance data.

Industrially fabricated thin-film modules are investigated by electroluminescence (EL) photography. We observe metastable transients in a series of successive images recorded during application of forward bias immediately after the Cu(In,Ga)Se2 modules were kept in the dark for several hours. Our experiments are conducted in the dark either under constant current (monitoring the module voltage) or vice versa. For both situations, the EL intensities increase with time, whereas we observe a decrease of the overall module voltage (at fixed current) or an increase of the current (at fixed voltage). We ascribe our observations to the simultaneous decrease of the bulk series resistance Rs and the reduction of recombination currents (an increase in the junction resistance Rj) during the forward bias soaking. A quantitative analysis of our data shows that the reduction of Rs we observe is much stronger than the increase of Rj. We also show that the bulk series resistance can strongly adulterate the determination of the sheet resistance of the front ZnO from EL images.

Deposition of MoSi2 films on silicon and tantalum substrates applying pulsed laser deposition technique has been performed. Crystalline, hexagonal symmetry, MoSi2 films were prepared directly from stoichiometric MoSi2 tetragonal target on room temperature and heated substrates (500 °C). Textured MoSi2 films having privileged (110) and (115) orientations and average crystallite size of about 105 nm were grown on Si(111) substrates with a good degree of axial texture (rocking curve full width half maximum of 1.5°). MoSi2 films grown on Ta(211) substrates, instead, turned out to be polycrystalline, with an average crystallite size of about 100 nm and 50 nm on substrates kept at room temperature and at 500 °C, respectively. Vickers hardness for 1.2 μm thick MoSi2 films on Si(111) substrates resulted to be 15 GPa both at room temperature and 500 °C, while for 0.4 μm thick MoSi2 films on Ta(211) substrates — 26 GPa at room temperature and 30 GPa at 500 °C.

The detailed balance model for quantum dot solar cells with quantum efficiencies above unity is extended to the case of non-ideal extraction of carriers from dots and finite mobilities of free carriers. For more realistic estimations of maximum efficiencies, we include experimental values for Auger lifetimes and absorption coefficients. Thus, for a given material, the model is capable of determining the critical values for the mobilities and extraction lifetimes, which are necessary to make the efficiency benefit from multiple exciton generation.

In this paper we review and discuss the effect of light illumination and of heating on polar order in electro-optic polymers and its practical implications. Both have a positive and negative influence. Light may create polar order but destroy it too. Similarly the heating increase the polar order by increasing the chromophore mobility, but in the same time it destroys it due to the increased chromophore diffusion. The mechanisms connected with these phenomena are presented and discussed.

In this work, we present structural and electrical properties of thin Si films which are homoepitaxially grown at low substrate temperatures (Ts = 450–700 °C) by high-rate electron beam evaporation. As substrates, monocrystalline Si wafers with (100) and (111) orientations and polycrystalline Si (poly-Si) seed layers on glass were used. Applying Secco etching, films grown on Si(111) wafers exhibit a decreasing etch pit density with increasing Ts. The best structural quality of the films was obtained on Si(100) wafers. Defect etching on epitaxially grown poly-Si absorbers reveal regions with different crystalline quality. Solar cells have been prepared on both wafers and seed layers. Applying Rapid Thermal Annealing (RTA) and Hydrogen plasma passivation an open circuit voltage of 570 mV for wafer based and 346 mV for seed layer based solar cells have been reached.

The method of electron beam induced currents in junction configuration (JEBIC) has been employed to investigate carrier collection in Cu(In,Ga)Se 2 solar cells. A detailed analysis of JEBIC line-scans reveals unexpected carrier collection properties, which cannot be explained with common models. We ascribe this anomalous behavior to an electrostatic barrier effect at the Cu(In,Ga)Se 2 / CdS interface. We suggest the existence of a thin defect-layer on the surface of the Cu(In,Ga)Se 2 with high acceptor concentration and valence band edge that is energetically lower than that of the bulk. Using this model, we achieve a good agreement between experimental and simulated JEBIC line-scans. The influence of the barrier effect is considerably reduced by a metastable change of the interface properties induced by intensive electron irradiation of the interface. This effect is explained by a metastable decrease of the negative charge density in the defect-layer.

The electroluminescence (EL) of high-efficiency mono-crystalline silicon solar cells is compared to that of polycrystalline ZnO/CdS/Cu(In,Ga)Se 2 heterojunction solar cells. Both types of devices exhibit a remarkable efficiency as light emitting diodes. The external quantum efficiency Q LED defined as the ratio between radiative and total recombination currents is Q LED ≈ 0.13% in case of the silicon cell and Q LED ≈ 0.03% for the Cu(In,Ga)Se 2 device. The luminescent emission of Cu(In,Ga)Se 2 changes from a broadened donor–acceptor pair recombination at temperatures T T > 200 K. The emission of the silicon cell is dominated by transverse optical phonon assisted band-to-band recombination in the entire temperature range 90 K ≤ T ≤ 300 K. The reciprocity between the external (photovoltaic) quantum efficiency Q e and the electroluminescent emission of both devices is fulfilled.

Fluorescent photon down conversion for the improvement of the blue response of ZnO/CdS/Cu(In,Ga)Se 2 heterojunction solar cells and modules is investigated. Fluorescent dyes of the series Lumogen® F are analyzed by optical transmission and reflection as well as by photoluminescence measurements. A spectral transfer matrix formalism is introduced that allows to predict the suitability of a luminescent dye as a down-converter for a given solar cell from its absorption/emission properties. We find that Lumogen® F Violet 570 and Lumogen® F Yellow 083 as well as a combination of both yields improvements for Cu(In,Ga)Se 2 solar modules. Particularly, we find that the short circuit current density of a Cu(In,Ga)Se 2 mini-module is improved by 1.5 mA cm − 2 when applying a varnish with a combination of Lumogen® F Violet and Yellow. About 0.5 mA cm − 2 of this improvement is due to a reduced overall reflectance and an improvement of 1 mA cm − 2 results from the frequency conversion by the dyes.

We investigated the opportunities to increase the electric uniformity of GaAs and InGaAs films grown by molecular-beam epitaxy (MBE) technique on monocrystalline (single crystal) GaAs: both on porous and conventional so-called “monolithic” (without pores) GaAs (100) substrates. The basic attention was given to study the electrically active defects in films by using scanning electron microscope (SEM) with new technique which is called “Rau-detector” [E.I. Rau, A.N. Zhukov and E.B. Yakimov, Solid-State Phenomena, 1998, v. 53–54, 327.]. We compared the main properties of epitaxial GaAs and InGaAs films grown on above mentioned substrates. The films grown on porous substrates had higher structural perfection including the following advantages: ( a ) smoother surface due to lateral growth mechanism; ( b ) less density of structural defects (without dislocation walls), the density of pyramidal defects was ∼ 2 × 10 5 cm − 2 as compared with the density 2 × 10 7 cm − 2 in the films grown on monolithic substrates; ( c ) less electrical activity of various structural defects and increased electric uniformity of grown films. The electrical activity of defects in films grown on porous substrates was essentially lowered due to gettering properties of porous substrate.

Large-grained polycrystalline silicon (poly-Si) films were prepared on glass using the 'seed layer concept' which is based on the epitaxial thickening of large-grained seed layers. The aluminium-induced layer exchange (ALILE) process was used to form p + -type seed layers on glass. The seed layers feature a preferential (100) orientation of the grain surface. Epitaxial growth of the p-type absorber layers was carried out at temperatures § 600°C by either electron cyclotron resonance chemical vapour deposition (ECRCVD) or electron-beam evaporation. Secco etching was used to analyse extended defects in the films epitaxially grown on ideal substrates (Si wafers). Opposed to ECRCVD, films grown with electron-beam evaporation show no etch pits when deposited on Si(100) wafers. Post-deposition treatments (defect annealing and defect passivation) were used to improve the quality of the absorber layers. Thin-film solar cells were prepared on both Si(100) wafers (ideal seed layer) and seed layer covered glass substrates by the deposition of an n + -type a-Si:H emitter and a TCO layer. The best solar cell results were

An equivalent circuit model consisting of parallel connected diodes with different electronic quality simulates the electronic properties of solar cells with spatially inhomogeneous material quality. Variations of the local saturation current density result in a degradation of the open circuit voltage, the fill factor and, in consequence, of the overall power conversion efficiency. However, a local series resistance introduced into this network limits this degradation by preventing areas with high saturation current density to dominate the electronic losses of the entire device. Analyzing the integral current/voltage curves of the networks shows the diode ideality larger than unity to result from spatially inhomogeneous saturation.

Silicon layers grown by low-temperature Electron Cyclotron Resonance Chemical Vapour Deposition (ECR-CVD) were investigated using photoluminescence (PL) and defect etching. Different forms of etch pits could be observed using Scanning Electron Microscopy. The densities of the etch pits and the intensities of defect-related PL bands are compared. A correlation between two kinds of elliptical etch pits, two PL peaks and the impurity content was found. One of these PL peaks has an energy of 903 meV, usually attributed to the so-called rod-like defects. The orientation of the related etch pits is, however, not consistent with the orientation of rod-like defects. Possible explanations for this behaviour are discussed.

Small-area Cu(In,Ga)Se 2 thin film solar cells have reached more than 19% efficiencies. Compared to other polycrystalline materials this efficiency value is remarkable. Nevertheless, the 19% for Cu(In,Ga)Se 2 range more than 6% (absolute) below the world's best single-crystalline Si cells and almost 14% below the upper theoretical limit of 33% for an ideal black body cell with infinitely large mobility and radiative recombination only. About 4% out of the 14% are of optical nature, additional 3% stem from the limited mobility/diffusion length and from band gap fluctuations with a standard deviation σ g ≈50 meV due to spatial variations of composition and stoichiometry of the quaternary compound Cu(In,Ga)Se 2 . Thus, about 26% efficiency would be possible if there were only these band gap fluctuations. Additional, voltage-dependent electrostatic potential fluctuations push down the efficiency further to 19%: The polycrystalline Cu(In,Ga)Se 2 which is unavoidably structurally inhomogeneous due to dislocations, grain boundaries, point defects, etc. is also electrostatically inhomogeneous because of charged defects. Electrostatic potential fluctuations at the valence and conduction band edge may be not only responsible for a high saturation current density but also for the ideality factor in the current/voltage curve. The band gap and electrostatic potential fluctuations make the effective band gap which controls the intrinsic carrier density smaller than the average optical gap. The (zero bias) electrostatic potential fluctuations are here derived from the ideality factors of the current/voltage curve. The ideality factor reflects the voltage-induced electrostatic homogenization of the sample. For the world's best Cu(In,Ga)Se 2 cells with an ideality factor of n id =1.5, we estimate zero bias electrostatic potential fluctuations with a standard deviation σ elec ≈140 meV.