Showing papers on "Polymer solar cell published in 1999"

Potential of amorphous silicon for solar cells

Abstract: This paper reviews recent developments in the field of amorphous-silicon-based thin-film solar cells and discusses potentials for further improvements. Creative efforts in materials research, device physics, and process engineering have led to highly efficient solar cells based on amorphous hydrogenated silicon. Sophisticated multijunction solar cell designs make use of its unique material properties and strongly suppress light induced degradation. Texture-etching of sputtered ZnO:Al films is presented as a novel technique to design optimized light trapping schemes for silicon thin-film solar cells in both p-i-n and n-i-p device structure. Necessary efforts will be discussed to close the efficiency gap between the highest stabilized efficiencies demonstrated on lab scale and efficiencies achieved in production. In case of a-Si:H/a-Si:H stacked cells prepared on glass substrates, significant reduction of process-related losses and the development of superior TCO substrates on large areas promise distinctly higher module efficiencies. A discussion of future perspectives comprises the potential of new deposition techniques and concepts combining the advantages of amorphous and crystalline silicon thin-film solar cells.

Charge Separation in Solid-State Dye-Sensitized Heterojunction Solar Cells

Abstract: Dye-sensitized nanocrystalline solar cells are presently under intensive investigation, as they offer an attractive alternative to conventional p--n junction devices. Solid-state versions have been described where the electrolyte present in the pores of the malodorous oxide film is replaced by a large band gap p-type semiconductor. In this way, a solid-state heterojunction of very large contact area is formed. Light is absorbed by the dye that is located at the interface. Upon excitation, the dye injects electrons into the conduction band of the oxide and is regenerated by hole injection into the p-type conductor. High incident photon-to-electric current conversion efficiencies have been achieved recently with a cell consisting of a dye-derivatized mesoporous TiO{sub 2} film contacted by a new organic hole conductor. The great advantage of such systems with regard to conventional p--n junctions is that only majority carriers are involved in the photoelectric conversion process. Moreover, these are generated by the dye precisely at the site of the junction where the electric field is maximal, enhancing charge separation. Photoelectric conversion by conventional solar cells involves minority carriers whose lifetime is restricted due to recombination. As they are generated throughout the semiconductor and away from the junction, expensive high-purity materialsmore » are required in order to maintain the minority carrier diffusion length at a level where current losses are avoided. While the dynamics of photoinduced redo processes in photoelectrochemical systems have been studied in great detail, little is known about the electron-transfer dynamics in solid-state sensitized junctions. Here the authors report for the first time on the direct observation of photoinduced, interfacial charge separation across a dye-sensitized solid-state heterojunction by means of picosecond transient absorption laser spectroscopy.« less

Origin of Photovoltage and Photocurrent in the Nanoporous Dye-Sensitized Electrochemical Solar Cell

Abstract: The essential role of the dark equilibrium potential is discussed for charge separation and the photovoltaic functioning of the title cell. A quantitative model is presented for the potential distribution in the sponge-type title cell. The unique screening process for the photogenerated electrons is discussed that facilitates their extremely long lifetime since the screening ions cannot function as recombination centers. A general analogy is pointed out for the photovoltaic functioning of the sponge-type electrochemical solar cell and of a conventional single-crystal solid-state solar cell.

Use of porous silicon antireflection coating in multicrystalline silicon solar cell processing

Abstract: The latest results on the use of porous silicon (PS) as an antireflection coating (ARC) in simplified processing for multicrystalline silicon solar cells are presented. The optimization of a PS selective emitter formation results in a 14.1% efficiency multicrystalline (5/spl times/5 cm/sup 2/) Si cell with evaporated contacts processed without texturization, surface passivation, or additional ARC deposition. Specific attention is given to the implementation of a PS ARC into an industrially compatible screen-printed solar cell process. Both the chemical and electrochemical PS ARC formation method are used in different solar cell processes, as well as on different multicrystalline silicon materials. Efficiencies between 12.1 and 13.2% are achieved on large-area (up to 164 cm/sup 2/) commercial Si solar cells.

Porous silicon in solar cell structures : a review of achievements and modern directions of further use

Abstract: Porous silicon, which is being obtained by electrochemical etching of silicon wafers in electrolytes on the base of hydrofluoric acid, recently attracted the attention of specialists in photovoltaics even more due to a number of its unique properties. However, at present, acceptable results are obtained for the use of porous silicon as antireflecting coating for silicon solar cells only. In the present paper, previous experience of the use of por-Si in the silicon solar cells has been reviewed. On the base of examination of the porous silicon properties, a number of new directions of improvement of photoconversion efficiency of structures with optimized layers of porous silicon are proposed. The results of numerical calculations carried confirm perspectiveness of use of porous silicon for efficiency improvement for different types of silicon solar cells. These can be increased of their internal quantum efficiency, expansions of operating spectral range toward ultra-violet and infrared spectrum range, decrease of losses of photogenerated power due to the influence of bulk and surface recombination.

High-Efficiency Amorphous Silicon Solar Cells with ZnO as Front Contact

Abstract: B-doped ZnO films deposited by the photo-induced metalorganic chemical vapor deposition (photo-MOCVD) method were applied to p-i-n single junction amorphous silicon (a-Si) solar cells as front contacts. The thickness and the doping level of the p-layer were optimized in order to increase the open-circuit voltage (Voc) of the fabricated a-Si solar cells. As a result, a stabilized conversion efficiency of 8.7% (Voc: 0.926 V, Jsc: 14.6 mA/cm2, FF: 0.646) was achieved under AM 1.5 (100 mW/cm2) illumination. Furthermore, the electrical properties of ZnO films were improved by employing an atomic layer deposition (ALD) technique instead of the conventional MOCVD method, and a lower resistivity of 5×10-4 Ωcm was achieved. It was also found that the stability of the electrical properties of ZnO films was improved by the ALD technique. The performance of the a-Si solar cells was further improved by applying the obtained high-quality ZnO films.

Light invariant, efficient, multiple band gap AlGaAs/Si/metal hydride solar cell

Abstract: Electronic and ionic charge transfer provides a basis for composite semiconductor/electrolyte systems featuring simultaneous solar/electrical conversion and solar energy storage. This cell contains both multiple band gap and electrochemical storage, and provides a nearly constant energetic output in illuminated or dark conditions. Multiple semiconductor band gaps can enhance the energetics of this interaction. The cell combines bipolar AlGaAs (Eg=1.6 eV) and Si (Eg=1.1 eV) and AB5 metal hydride/NiOOH storage, and generates a light variation insensitive potential of 1.2–1.3 V at total (including storage losses) solar/electrical energy conversion efficiency of 18.1%.

Silicon thin-film, integrated solar cell, module, and methods of manufacturing the same

Abstract: A polycrystalline film of silicon including silicon grains having an aspect ratio, d/t, of more than 1:1, wherein “d” is the grain diameter and “t” is the grain thickness. The polycrystalline film of silicon can be used to form an electronic device, such as a monolithically integrated solar cell having ohmic contacts formed on opposed surfaces or on the same surface of the film. A plurality of solar cells can be monolithically integrated to provide a solar cell module that includes an electrically insulating substrate and at least two solar cells disposed on the substrate in physical isolation from one another. Methods for manufacturing the film, solar cell and solar cell module are also disclosed. The simplified structure and method allow for substantial cost reduction on a mass-production scale, at least in part due to the high aspect ratio silicon grains in the film.

Novel profiled thin-film polycrystalline silicon solar cells on stainless steel substrates

Abstract: In order to obtain higher conversion efficiencies while keeping the manufacturing cost low in thin-film PV technologies, a possible low bandgap material is amorphous silicon germanium. Although record efficiencies in excess of 15% have been reported for triple-junction solar cells comprising these alloys, concerns regarding the stability and quality of this material still need to be overcome. Another approach is the introduction of thin-film micro- or polycrystalline silicon with a band gap of 1.1 eV, deposited at a temperature that is low enough to allow cheap, "foreign" carrier materials. Apart from the application of a modified PECVD method utilizing frequencies in the VHP domain, the hot wire CVD (HWCVD) method appears a particularly promising technique for the deposition of high-quality thin-film intrinsic or doped poly-Si. In this contribution, special attention will be paid to the latest developments in the application of hot-wire deposited silicon thin films in solar cells. By implementing a profiled hydrogen-diluted HWCVD growth scheme that produces a thin small-grained seed layer on top of a thin n-layer, we have been able to obtain fast polycrystalline growth of the intrinsic layer of an n-i-p solar cell. An efficiency of 4.41% is obtained and the fill factor is 0.607. The current density is close to 20 mA/cm/sup 2/ for an i-layer that is only 1.22 /spl mu/m thick. The cell is deposited on plain stainless steel and thus does not comprise a back reflector.

New developments in amorphous thin-film silicon solar cells

Abstract: Thin-film silicon solar cells usually contain amorphous silicon layers made by plasma enhanced chemical vapor deposition (PECVD). This CVD method has the advantage that large-area devices can be manufactured at a low processing temperature, thus facilitating low-cost solar cells on glass, metal foil, or polymer foil. In order to obtain higher conversion efficiencies while keeping the manufacturing cost low, a new development is to introduce low bandgap materials in a multijunction device structure. A frequently used low bandgap material is amorphous silicon-germanium. Record initial efficiencies in excess of 15% have been reported for triple-junction solar cells comprising these alloys. In this paper, we present a novel manufacturing method for amorphous silicon based tandem cells suitable for roll-to-roll production.

Low Temperature Deposition of Amorphous Silicon Based Solar Cells

Abstract: Our investigations study the influence of various deposition parameters on the structural and optoelectronic properties of a-Si:H deposited at temperatures of 100 °C and below. Despite a significant material quality deterioration at low substrate temperatures, we observe remarkable improvements of charge carrier transport properties due to an increased H2-dilution of the process gases. In case of doped layers, we restore the electrical conductivity of low temperature n-type a-Si:H to standard values, whereas the p-layer quality is still inferior. We incorporate our optimized low temperature layers into a variety of solar cell types, including single and tandem cell structures. In addition to our conventional pin-structures we also successfully develop nip-cells for growth on opaque polymer substrates. From pinpin tandem cells, we record initial efficiencies of 6.0 % at a deposition temperature of 100 °C and 3.8 % at 75 °C. Interestingly, our nipnip tandem structures attain similar values which offers the possibility for deposition on low-cost plastic substrates. The mechanical flexibility of such substrates offers a wide variety of novel applications.

High-temperature processing of crystalline silicon thin-film solar cells

Abstract: The crystalline silicon thin-film solar cell combines, in principle, the advantages of crystalline silicon wafer-based solar cells and of thin-film solar cell technologies. Its efficiency potential is the highest of all thin-film cells. In the “high-temperature approach” thin silicon layers are deposited on substrates that withstand processing temperatures higher than 1000 °C. The basic features of the high-temperature crystalline silicon thin-film cell technology are described and some important results are discussed.

The role of ZnO:Al films in the performance of amorphous-silicon based tandem solar cells

Abstract: Degradation of textured :F films in glow-discharge hydrogen plasmas has been minimized by deposition ZnO:Al films onto them. This coating also prevents the diffusion of Sn atoms from :F into the stacked silicon layers of solar cells, while the transmittance and sheet resistivity remain unaltered. Another important aspect is the rear reflection at the back contact. Use of a :Al layer as a back reflector at the /metal interface in a-Si:H tandem solar cells has been found to absorb light of the long-wavelength ( nm) region in the solar spectrum. This improves the short-circuit current density and thereby the efficiency of amorphous silicon solar cells to a great extent.

Amorphous silicon solar cell

Abstract: An amorphous silicon solar cell includes a substrate, a transparent electrode formed on this substrate, a power-generating film formed on this transparent electrode, and a back-side electrode formed on this power-generating film. The power-generating film is formed by sequentially stacking p-type/i-type/n-type hydrogenated amorphous silicon layers. The defect density of the i-type hydrogenated amorphous silicon layer is less than 1015 defects/cc.

Solar cell and method for fabricating a solar cell

Abstract: There is disclosed a method for fabricating a solar cell (10) comprising at least forming a phosphorus-containing junction layer (2) having a n ++ part (3) in which phosphorus is doped at high concentration on the front surface of a P type silicon substrate (1), forming a front surface electrode on the n ++ part, and forming a back surface electrode on the back surface of the P type silicon substrate, characterized in that the phosphorus-containing junction layer having the n ++ part (3) on the front surface is formed by printing an organic silica compound paste containing phosphorus on the P type silicon substrate in a pattern corresponding to a pattern of the front surface electrode (6), and subjecting the P type silicon substrate to vapor phase phosphorus diffusion heat treatment, and a solar cell fabricated by the method. There can be provided a method for fabricating a solar cell having high efficiency in high productivity

Boron ion-implanted C60 heterojunction photovoltaic devices

Abstract: An attempt has been made on the device fabrication with boron ion-implanted C60 thin films grown on n-type Si (100) by molecular-beam epitaxy. The studies on the films implanted to a dose of 1×1014 ions/cm2 with multiple B ion energies in the range of 50–80 keV reveal p-type conduction in the B ion-implanted C60 thin films as a result of amorphous carbon layer formation by B ion implantation. In addition, p-type B-implanted C60/n-type Si heterojunction solar cells with a conversion efficiency as high as 0.02% higher than previous highest value ever reported have been fabricated. The photovoltaic properties of the solar-cell structure are discussed along with the dark and illuminated I–V characteristics.

Why is the open-circuit voltage of crystalline Si solar cells so critically dependent on emitter- and base-doping?

Abstract: This paper discusses the critical dependence of the open-circuit voltage (VOC) of crystalline Si solar cells on the emitter and base doping levels. Contrary to conventional models that try to ascribe VOC-limitations to (independent) bulk and surface recombination losses, the authors suggest, as the dominant mechanism, the formation of a compensated ``buffer layer'' that is formed as phosphorus is diffused into the p-type (boron-doped) base. The only purpose of the base doping is to optimize the buffer layer. Their calculations show that this model makes the achievement of high VOC and good carrier collection (JSC, FF) interdependent. Sanyo's ``HIT'' solar cells are an example of a different method to implement this buffer layer concept for crystalline Si solar cells. The general principle for a VOC-enhancing buffer layer relies on using materials with high lifetimes and low carrier mobilities that are capable of reducing surface or junction recombination by reducing the flow of carriers into this loss-pathway.

Structural changes in InP/Si solar cells following irradiation with protons to very high fluences

Abstract: Precisely how the short circuit current (JSC) is produced in a proton irradiated n+p InP/Si solar cell at very high fluence levels has been determined from combined measurements of the cell structure using electrochemical capacitance–voltage profiling and detailed analysis of the spectral quantum efficiency. Type conversion in the base region of the cell is shown to occur before an anomalous peak in the degradation curve for JSC is reached at high damage levels. The short circuit current, and hence the cell efficiency, ultimately collapse because the high absorption coefficient of InP eventually prevents the generation of electron–hole pairs close enough to the effective cell junction from being collected.

Characterization of large area flexible plastic solar cells based on conjugated polymer/fullerene composites

Abstract: The development of solar cells based on composites of organic conjugated semi-conducting polymers with fullerene derivatives can provide a new method in the exploitation of solar energy. Organic solar cells must fulfill the criteria of stability, efficiency and reduction of production costs to find new applications. Specially, the bulk donor-acceptor heterojunctions between conjugated polymers and fullerenes have been successfully utilized for photovoltaic devices with high carrier collection efficiency compared to the devices made from single components. In this work we present measurements of the photovoltaic response of bulk donor-acceptor heterojunction between the conjugated polymer (as a donor, D) poly(3- octylthiophene), P3OT and fullerenes, (as acceptor, A), deposited between indium tin oxide and aluminum electrodes. These devices are based on ultrafast, reversible, metastable photoinduced electron transfer and charge separation.

Heterostructure solar cells

Abstract: Heterostructure solar cells based on III–V compounds are studied. Record-high efficiencies are obtained for solar cells based on AlGaAs/GaAs heterostructures: 24.6% for 100-fold concentration of sunlight in outer space (AM0) and 27.5% for 100-fold concentration of the light on the ground (AM1.5). A substantial increase in radiation resistance is obtained for solar cells with a built-in Bragg mirror. Cascaded solar cells with efficiencies of up to 32% for 100 suns (AM1.5) are created and studied; in these cells the upper wide-gap materials are infrared transparent elements based on GaAs, while the lower narrow-band elements are made of GaSb or an InGaAs solid solution.

Encapulation process for mono-and polycrystalline silicon solar cell modules

Abstract: A crystalline silicon based solar cell module comprising: (a) a crystalline silicon based solar cell array formed by interconnecting a plurality of crystalline silicon based solar cells with an interconnect; (b) a hot melt adhesive applied above and below the interconnect to reduce mechanical and thermal stress between the interconnect and the crystalline silicon based solar cells. The hot melt adhesive can be an ethylene-polymer along with a variety of additives such as oxidation inhibitor, UV stabilizer, and UV absorber.