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In the future solar devices will be manufactured onto thin mono-crystalline silicon wafers (foils) potentially bonded to substrate carriers. In this study, the influence of the substrate carrier potential (grounded or floating) on the amorphous silicon a-Si:H surface passivation of the bonded foil is discussed for the cases of conductive and insulating substrate carriers. A conductive carrier leads to an increase in deposition rate and ion bombardment energy, which is detrimental for sample lifetime. An insulating carrier, e.g., a glass substrate, inverts the trend and improves the a-Si:H surface passivation. [ABSTRACT FROM AUTHOR]

We have investigated fine grained polycrystalline silicon thin films grown by direct chemical vapor deposition on oxidized silicon substrates. More specifically, we analyze the influence of the doping type on the properties of this model polycrystalline silicon material. This includes an investigation of defect passivation and benchmarking of minority carrier properties. In our investigation, we use a variety of characterization techniques to probe the properties of the investigated polycrystalline silicon thin films, including Fourier Transform Photoelectron Spectroscopy, Electron Spin Resonance, Conductivity Activation, and Suns-Voc measurements. Amphoteric silicon dangling bond defects are identified as the most prominent defect type present in these layers. They are the primary recombination center in the relatively lowly doped polysilicon thin films at the heart of the current investigation. In contrast with the case of solar cells based on Czochralski silicon or multicrystalline silicon wafers, we conclude that no benefit is found to be associated with the use of n-type dopants over p-type dopants in the active absorber of the investigated polycrystalline silicon thin-film solar cells. [ABSTRACT FROM AUTHOR]

Abstract: To answer the challenge of less expensive renewable electricity, the photovoltaics community is focusing on producing thinner silicon solar cells. A few years ago, in the field of silicon-on-nothing structures, micron-thick monocrystalline layers suspended over their parent wafer were produced by high-temperature annealing of specific arrays of macropores. Those macropores reorganise into one single void and leave a thin overlayer on top. Since this method may be an inexpensive way of fabricating high-quality silicon films, this paper investigates its potential for photovoltaic applications. In particular, we investigated if large surfaces can be produced and transferred to foreign substrates with this method. We fabricated basic solar cells, without rear-surface passivation, on 5cm×5cm-large and 1-μm-thick films transferred to glass, that showed energy-conversion efficiencies up to 2.6%. These cells demonstrate the feasibility of the presented concept as a layer-transfer process for solar-cell application. After formation by annealing, the film is only barely attached to its parent wafer, but can still safely be handled provided that any abrupt gas flow or pumping to vacuum is avoided. After transfer and permanent bonding, the sample can be handled as any bulk wafer. [Copyright &y& Elsevier]

Abstract: Thin layers of silicon for solar cells can be lifted-off from wafers by taking advantage of the property of macropores to reorganise at high temperature and, in specific conditions, to form a high-quality layer on top of an empty space. Those conditions need to be identified and this work focuses in particular on the annealing ambient composition. Its influence was investigated by scanning and transmission electron microscopy and by Fourier-transform infrared spectroscopy. Apart from hydrogen, which has been used in previous studies, argon was found to be also compatible with the reorganisation. This result points out that the presence of oxygen impurities may not be as deleterious as expected, but that those impurities complicate the set of reactions taking place during the high-temperature process. [Copyright &y& Elsevier]

Abstract: The effect of temperature and composition on the I–V characteristics of blends of (poly(2-methoxy-5-(2′-ethyl-hexyloxy)-l,4-phenylene vinylene) (MEH-PPV), and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) sandwiched between a transparent indium tin oxide (ITO) electrode and an Al backside contact (solar cell structure) are investigated. The observed dark I–V curves agree well with the trap-controlled space charge limited transport theory. The illuminated I–V curves do not obey the theory of space charge limited currents. The short-circuit currents in the illuminated samples depend strongly on the composition. The current is maximum for the 80% PCBM concentration in the blend. The open circuit voltage also depends on the composition. It is maximum for 0% PCBM concentration and decreases monotonically with PCBM concentration. This might lead to the conclusion that the open circuit voltage is due to internal bulk heterojunctions (BHs). However, we have pointed out that this conclusion, arrived at by earlier workers also, is not necessarily valid. The superposition principle is not valid but the discrepancy is small. [Copyright &y& Elsevier]

A promising cost-effective way of converting sun light into electricity could be a solar cell realized in a thin monocrystalline silicon film, due to its potential to achieve cell efficiencies of more than 20% in a 20 μm thick film. A porous silicon layer transfer technique provides an opportunity to get monocrystalline films on low-cost substrates such as glass. This paper reviews various processes, which are being developed for the layer transfer using porous silicon as a sacrificial layer while reusing of starting silicon substrate. The four basic steps—porous silicon formation, active layer deposition, layer separation and transfer, and device fabrication—have been identified in layer transfer process. The processes have been categorized and compared on the basis of the sequence of steps used in individual processes. [Copyright &y& Elsevier]

Thin film monocrystalline silicon solar cells based on porous silicon (PS) layer transfer processes could be cost-effective because of their lower consumption of material use and the potential for high efficiency. The process is based on our ability to separate thin porous films (p+) of desired thickness and area from Si substrate. Crystallinity of these porous films is studied with XRD for their suitability for Si epitaxy. AFM is employed to study the Si substrate surface roughness after one or more porous film separations. The roughness stabilizes after four film separations. Annealing of the porous films at temperatures above 1050 °C results in a closed surface, suitable for Si epitaxy. XRD analysis of epitaxially deposited Si layer on annealed PS film revealed its high mono-crystalline quality. A FMS solar cell of 12% efficiency has been realized in an 18 μm thin epitaxial layer. [Copyright &y& Elsevier]

Aluminum-induced crystallization of a-Si is a promising path to cheap and simple definition of a seeding layer for epitaxial growth of a large-grained active layer in thin-film polycrystalline silicon solar cells on foreign substrates. The course of the crystallization has been shown to depend on a variety of factors such as temperature and deposition conditions of the aluminum and silicon layers. We suggest a dependency on the characteristics of the materials involved in the reaction, focusing particularly on the different reactivity of a-Si deposited with different deposition techniques (e-beam evaporation vs. PECVD). First results of high-temperature layer growth on the seeding layers and cell fabrication are also reported. [Copyright &y& Elsevier]

Basic solar cell characteristics are examined in bulk donor-acceptor-heterojunction devices. Therefore, spin-coated organic blends of poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene-vinylene) (MDMO-PPV) and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) are used as active material sandwiched between a transparent IndiumTinOxide (ITO)-electrode and an Al backside contact. A comparison is made between cells with or without an extra interfacial layer of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) on top of the ITO-electrode. Furthermore, the effect of the thickness of the active layer on the photovoltaic performance of the devices is studied. It is seen that applying this extra PEDOT/PSS layer results in an important increase of the contact component of the series resistance of the cells. At the same time, open circuit voltage improved for devices with an interfacial layer while the fill factor was higher for cells with no PEDOT/PSS film. For thinner active layers, in both cases the bulk component of the series resistance decreased. Nevertheless, a decrease of short circuit current is seen at reduced illumination. Shunt resistance shows a slight increase resulting in an improvement of open circuit voltage. Also, the fill factor increases for thinner active layers. For the thinnest standard devices a power conversion efficiency of over 3% could be measured under AM1.5 conditions. [Copyright &y& Elsevier]

An overview is given concerning industrial technologies, IMEC's advanced pilot line crystalline silicon solar cell technologies and medium term developments for industrial crystalline silicon terrestrial solar cell fabrication. Also IMEC's work on thin film crystalline silicon solar cells is shortly presented, all of this taking into account the existing market and technology trends. [ABSTRACT FROM AUTHOR]

Presents the preparation of polycrystalline silicon solar cells using a conventional diffusion and screen printed metallization method. Application of a dicing saw and beveled blades for the V-groove formation; Comparison with the standard nongrooved structure.

Examines the passivation of solar cells fabricated using casted multicrystalline silicon from Eurosolare. Description of the optimum passivation scheme; Increase of the efficacy of the solar cells with the combination of phosphorus gettering and read aluminum treatments.

Describes a fabrication process for blue response improvement in low-cost polycrystalline silicon solar cells. Creation of a selective emitter; Comparison of the parameters of solar cells with different types of emitters; Advantages of the proposed process.