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[en] In order to estimate the performance of solar cells with downshifters under realistic irradiation conditions we used spectral distributions as they may be found outdoors. The spectral distributions were generated on a minutely basis by means of the spectrum simulation model SEDES2, using minutely measured data for global, direct, and diffuse irradiation from a Dutch meteorological station. Hourly aggregated spectra for a number of typical days (clear summer day, cloudy summer day, clear winter day, cloudy winter day) were used in modelling the output of the solar cell with and without downshifter. It was found that the simulated short current enhancement, which varies between about 7 and 23%, is linearly related with the average photon energy of the spectra
[en] Pulsed laser sources are widely used for the micro-processing of materials from the structuring and patterning of surfaces to the direct machining of devices. This paper discusses laser micro-processing techniques for the fabrication of microstructures with high accuracy and precision over large areas. Techniques discussed include laser mask projection techniques, synchronised image scanning (SIS) and bow tie scanning (BTS) and direct beam micromachining. Examples of the application of these techniques in industrial production are discussed, including solar cell scribing, micro-optical device manufacture, inkjet printer nozzle drilling and plasma display panel patterning
[en] Structuring of glassy carbon (GC) can be performed by various methods such as sawing, laser ablation, and reactive ion etching (RIE). Laser machining with a tripled Nd:YAG laser at an irradiation wavelength of 355 nm allows the fabrication of V-shaped channels with depths >600 μm and aspect ratios >5. This method is very flexible for rapid prototyping, but is comparatively slow due to the sequential machining. A complete flowfield consisting of 100 parallel channels with a depth of 250 μm and a top width of 50 μm was prepared by direct laser ablation and tested in a micro fuel cell. As an alternative, a novel process combining laser structuring of a metal mask with subsequent reactive ion etching was developed. The quality of the metal layer and the ablation behavior are strongly influenced by the metal adhesion, which depends on the GC pretreatment and the deposition technique. Reactive ion etching of glassy carbon can be performed with etch rates of ∼40 μm h-1, but the high pressure conditions of 100 mTorr (0.13 mbar) limit the aspect ratio to <1.5 due to pronounced underetching. The fabrication of structures with aspect ratios >4 and etch rates of ∼10 μm h-1 is possible with the use of alternative etching devices with different design or plasma sources
[en] In-situ Se flux control system is applied for the growth of Cu(In,Ga)Se2 (CIGS) absorber layers by a multi stage thermal co-deposition of elements at low substrate temperature below 500 °C. It was revealed that the composition depth profile of the [Ga]/([In]+[Ga]) (GGI) ratio is affected by the [Se]/[Metal] flux ratio. It was observed for the solar cell properties that the change in the depth profiles of GGI induced by the change of [Se]/[Metal] resulted in an increase in the JSC and a decrease in the FF, and hence little influence on the efficiency. Under control of [Se]/[Metal] ratio during the deposition process, the effect of CIGS layer thickness on the solar cell properties was investigated. With increase in the thickness up to 2.8 μm, the short circuit current density was increased to over 35 mA/cm2 w/o AR coating, resulting in conversion efficiency above 18% using low temperature deposition method. - Highlights: • Precise control of Se flux during the growth of Cu(In,Ga)Se2 absorber layers • The Se to metals flux ratio affects the composition depth profile of the [Ga]/([In]+[Ga]) • Improvements of JSC and efficiency with increasing the Cu(In,Ga)Se2 layer thickness
[en] ‘Smart’ (or selective) electrode for charge carriers, both electrons and holes, in organic bulk-heterojunction (BHJ) solar cells using insertion layers made of hydrophobically-recovered and contact-printed siloxane oligomers between electrodes and active material has been demonstrated. The siloxane oligomer insertion layer has been formed at a given interface simply by conformally-contacting a cured slab of polydimethylsiloxane stamp for less than 100 s. All the devices, either siloxane oligomer printed at one interface only or printed at both interfaces, showed efficiency enhancement when compared to non-printed ones. The possible mechanism that is responsible for the observed efficiency enhancement has been discussed based on the point of optimum symmetry and photocurrent analysis. Besides its simplicity and large-area applicability, the demonstrated contact-printing technique does not involve any vacuum or wet processing steps and thus can be very useful for the roll-based, continuous production scheme for organic BHJ solar cells. - Highlights: • Carrier-selective insertion layer in organic bulk heterojunction solar cells • Simple contact-printing of siloxane oligomers improves cell efficiency. • Printed siloxane layer reduces carrier recombination at electrode surfaces. • Siloxane insertion layer works equally well at both electrode surfaces. • Patterned PDMS stamp shortens the printing time within 100 s
[en] The paper presents a two-dimensional simulation study of a polycrystalline Cu(In,Ga)Se2 (CIGS) solar cell with various shapes of grains inside the CIGS absorber layer. The grain boundaries (GBs) with a diverse valence-band offset (VBO) and the density of defect states (NtA) are considered so as to evaluate their effects on the performance of the CIGS cell. The numerical simulations show that a CIGS cell with column-like grains can achieve a high conversion efficiency (η), while the η of a CIGS cell with diamond-like grains is low if the VBO at the GBs exceeds 0.4 eV. The VBO at which the η of the CIGS cell with diamond-like grains peaks is found at 0.20-0.27 eV. A favorable VBO mainly depends on the shape of the grains, but it also depends on the NtA. The simulations of the CIGS cells in the substrate and superstrate configurations showed that their performances change if the VBO is varied. This result also implies that the configuration of the CIGS cell is important and the substrate configuration with larger grains in the space-charge region has a considerable advantage if the VBO ranges from 0 eV to 0.2 eV.
[en] We report the effects of precursor uniformity on the efficiency of Cu2ZnSnSxSe4−x (CZTSSe) solar cells using sputtered precursors. The reduction of Sn cluster agglomeration in the Cu/Sn/Zn stacked precursor created synthesis of more uniformly distributed CZTSSe absorbers during the annealing process. The secondary phase difference between the 80 W and 40 W sputtered CZTSSe absorbers was confirmed with Raman analysis at 178 cm−1 and 259 cm−1. The 40 W sputtered CZTSSe cell produced blue region enhancement of external quantum efficiency results due to improvement of the pn-junction properties. The CZTSSe 40 W cells achieved a maximum power conversion efficiency of 5.7% and short-circuit current of 32.4 mA/cm2. - Highlights: • The sputtering conditions influence the morphology of the precursor. • The morphology of the precursor depends on the tin cluster agglomeration. • A flatter surface of the precursor provides higher solar cell efficiency.
[en] In this investigation we selected four different Cu(In,Ga)Se2-based solar cells produced using different methods and with efficiencies ranging from less than 5% for the low-cost types to 20% for the highest efficiency process. These devices were intensively characterized using the optoelectronic methods of temperature-dependent current–voltage characteristics, capacitance–voltage measurements, and bias-dependent external quantum efficiency. By combining these methods it is possible to study the dominant recombination mechanisms in the devices and relate them to composition and morphology effects known through other characterization series. It was found that the highest efficiency cell has the least indication of interface recombination or tunneling effects; the temperature-dependent behavior is best described by recombination in the space-charge region. In contrast, the low-cost devices reveal high diode factors and a temperature dependence well described by tunneling-enhanced recombination at the interface. The consequences for the device behavior and recommendations for improvement will be presented. - Highlights: ► Highly efficient and low-cost Cu(In,Ga)Se2 solar cells are investigated. ► Recombination mechanisms are determined. ► Current collection is studied by bias-dependent spectral photocurrent measurement. ► Activation energy is low for interface-dominated recombination
[en] In this paper we analyse the passivation of the front surface of p-Si interdigitated rear contacts solar cell (IBC) by a thin porous silicon (PS) layer. Effectively, an efficiency improvement of 87% in relative was observed after porous silicon layer formation on the front surface of the IBC cell. The origin of surface passivation by the PS layer was studied by Laser Beam Induced Current (LBIC) method. The front surface of rear contacts cell with thin porous silicon layer was scanned by a modulated red laser beam in presence of a permanent light with different wavelengths and intensities. It was shown that without permanent illumination, the photocurrent of the cell with PS layer is very low, even lower than for a cell with unpassivated surface. However with short permanent wavelength illumination a strong increase of photocurrent was observed (8-10 times!). The light-dependent porous silicon passivation phenomenon is explained by a significant negative charge accumulation at the PS/p-Si interface traps under illumination. This leads to the formation of a hi-low (p+/p) junction at the front surface of the cell and to the reduction of the front surface recombination rate, like in Front Surface Field Solar Cell
[en] Several non-vacuum based approaches have been employed to deposit the Cu(In,Ga)Se2 layer in photovoltaic devices, but most of them use processing temperatures in the vicinity of 500 °C. Here, we present the results on a facile solution-based deposition technique for CuInSe2 (CISe) and CuIn(S,Se)2 (CISSe) thin films with deposition temperatures of 300 °C. CuxSe (1.5 ≤ x ≤ 2) or CuyS (1 ≤ y ≤ 2) precursor films deposited on a substrate were reacted with InCl3 and Se reactants in oleylamine to form CISe or CISSe thin films of the desired thickness, composition and crystal structure. Solar cells processed from these films on Mo-coated glass substrates demonstrated an efficiency of 2% under AM 1.5 illumination. We also present external quantum efficiency and capacitance–voltage measurements from these devices providing insights into the device performance. - Highlights: ► We present a solution-based deposition technique for CuInSe2 films at 300 °C. ► Lower temperatures, same number of steps enable processing on flexible substrates. ► Solar cells demonstrate an efficiency of 2%.