Showing papers on "Polymer solar cell published in 2001"

Fabrication of bulk heterojunction plastic solar cells by screen printing

Abstract: We demonstrate the use of screen printing in the fabrication of ultrasmooth organic-based solar cells. Organic films on the order of several tens of nanometers in thickness and 2.6 nm surface roughness were made. The first-generation screen-printed plastic solar cells demonstrated 4.3% in power conversion efficiency when using an aluminum electrode and 488 nm illumination.

Synthesis and characterization of a low bandgap conjugated polymer for bulk heterojunction photovoltaic cells

Abstract: Low optical bandgap conjugated polymers may improve the efficiency of organic photovoltaic devices by increasing the absorption in the visible and near infrared region of the solar spectrum. Here we demonstrate that condensation polymerization of 2,5-bis(5-trimethylstannyl-2-thienyl)-N-dodecylpyrrole and 4,7-dibromo-2,1,3-benzothiadiazole in the presence of Pd(PPh3)2Cl2 as a catalyst affords a novel conjugated oligomeric material (PTPTB), which exhibits a low optical bandgap as a result of the alternation of electron-rich and electron-deficient units along the chain. By varying the molar ratio of the monomers in the reaction and fractionation of the reaction product, two different molecular weight fractions (PTPTB-I and PTPTB-II, see Experimental section) were isolated, containing 5–17 and 13–33 aromatic units respectively, as inferred from matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Thin films of PTPTB-I and PTPTB-II exhibit an optical bandgap of 1.60 and 1.46 eV, respectively. Photoinduced absorption (PIA) and photoluminescence spectroscopy of blends of PTPTB-I and a methanofullerene (1-(3-methoxycarbonyl)-propyl-1-phenyl-[6,6]C61, PCBM) gave direct spectral evidence of the photoinduced electron-transfer reaction from PTPTB-I as a donor to the fullerene derivative as an acceptor. Thin PTPTB-I:PCBM composite films were sandwiched between indium tin oxide/poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonic acid) (ITO/PEDOT:PSS) and Al electrodes to prepare working photovoltaic devices, which show an open circuit voltage of 0.67 V under white-light illumination. The spectral dependence of the device shows an onset of the photocurrent at 1.65 eV (750 nm).

Surface passivation of silicon solar cells using plasma-enhanced chemical-vapour-deposited SiN films and thin thermal SiO2/plasma SiN stacks

Abstract: Two different techniques for the electronic surface passivation of silicon solar cells, the plasma-enhanced chemical vapour deposition of silicon nitride (SiN) and the fabrication of thin thermal silicon oxide/plasma SiN stack structures, are investigated. It is demonstrated that, despite their low thermal budget, both techniques are capable of giving an outstanding surface passivation quality on the low-resistivity (∼1 � cm) p-Si base as well as on n + -diffused solar cell emitters with the oxide/nitride stacks showing a much better thermal stability. Both techniques are then applied to fabricate frontand rear-passivated silicon solar cells. Open-circuit voltages in the vicinity of 670 mV are obtained with both passivation techniques on float-zone single-crystalline silicon wafers, demonstrating the outstanding surface passivation quality of the applied passivation schemes on real devices. All-SiN passivated multicrystalline silicon solar cells achieve an open-circuit voltage of 655 mV, which is amongst the highest open-circuit voltages attained on this kind of substrate material. The high open-circuit voltage of the multicrystalline silicon solar cells results not only from the excellent degree of surface passivation but also from the ability of the cell fabrication to maintain a relatively high bulk lifetime (>20 µs) due to the low thermal budget of the surface passivation process.

Surface recombination velocity of phosphorus-diffused silicon solar cell emitters passivated with plasma enhanced chemical vapor deposited silicon nitride and thermal silicon oxide

Abstract: This work was supported by funding from the Australian Research Council. One of the authors ~J.S.! gratefully acknowledges the support of a Feodor Lynen fellowship by the Alexander von Humboldt Foundation of Germany.

Temperature dependence for the photovoltaic device parameters of polymer-fullerene solar cells under operating conditions

Abstract: We report on the temperature dependence of various photovoltaic device parameters of solar cells, fabricated from interpenetrating networks of conjugated polymers with fullerenes, in the wide temperature range of their possible operating conditions ~25‐ 60 °C!. The open-circuit voltage was found to decrease linearly with increasing temperature. For the short-circuit current, we observed a monotonic increase with increasing temperature, followed by a saturation region. The rate of this increase ~coupled to a corresponding increase for the fill factor! was found to overtake the corresponding rate of decrease in voltage, resulting in an overall increase of the energy conversion efficiency. The efficiency was observed to reach a maximum value in the approximate range 47‐ 60 °C. The results are discussed with respect to possible mechanisms for photovoltage generation and charge carrier transport in the conjugated polymer-fullerene composite, and in particular, thermally activated charge carrier mobility. © 2001 American Institute of Physics. @DOI: 10.1063/1.1412270#

Thin-film solar cell fabricated on a flexible metallic substrate

Abstract: A thin-film solar cell (10) is provided. The thin-film solar cell (10) comprises a flexible metallic substrate (12) having a first surface and a second surface. A back metal contact layer (16) is deposited on the first surface of the flexible metallic substrate (12). A semiconductor absorber layer (14) is deposited on the back metal contact. A photoactive film deposited on the semiconductor absorber layer (14) forms a heterojunction structure and a grid contact (24) deposited on the heterjunction structure. The flexible metal substrate (12) can be constructed of either aluminium or stainless steel. Furthermore, a method of constructing a solar cell is provided. The method comprises providing an aluminum substrate (12), depositing a semiconductor absorber layer (14) on the aluminum substrate (12), and insulating the aluminum substrate (12) from the semiconductor absorber layer (14) to inhibit reaction between the aluminum substrate (12) and the semiconductor absorber layer (14).

Enhanced Efficiency of a Dye-Sensitized Solar Cell Made from MgO-Coated Nanocrystalline SnO2

Abstract: Nanocrystalline SnO2-based dye-sensitized photoelectrochemical solar cells have very low open-circuit voltages of 325–375 mV and efficiencies of ~ 1%. However, on coating the SnO2 crystallites with a thin film of MgO, the voltage and efficiency are increased to 650–700 mV and ~ 6.5%, respectively. Evidence is presented to show that the photoexcited dye on the outer MgO shell could tunnel electrons to SnO2 and that the low probability of reverse tunneling suppresses recombinations, thus increasing the efficiency. An explanation is also given as to understand why dye-sensitized TiO2 cells are more efficient than those made from SnO2 alone.

Effects of Substrate Surface Morphology on Microcrystalline Silicon Solar Cells

Abstract: The relationship between µc-Si:H solar cell performance and surface morphology of substrate is studied systematically using textured-ZnO substrate which is formed by wet etching process in order to clarify the optimum morphology of substrate for high efficiency. An average slope, tan θ, of substrate surface textures is obtained by analysis of atomic force microscopy (AFM) images, and solar cell performance is correlated with the value os tan θ. As a result, because of the balance between the optical confinement and the grain boundary formation, a conversion efficiency shows a maximum at a tan θ of 0.08 which is 3 times smaller as compared to that used for a-Si:H. An efficiency of 9.4% (Voc=0.526 V, Jsc=25.3 mA/cm2, FF=0.710) is obtained at a deposition temperature of 140°C using the optimized morphology.

Electron Transfer Dynamics in Dye Sensitized Nanocrystalline Solar Cells Using a Polymer Electrolyte

Abstract: Transient absorption spectroscopy was employed to study electron-transfer dynamics in dye sensitized nanocrystalline solar cells incorporating a polymer electrolyte, poly(epichlorohydrin-co-ethylene oxide) containing NaI and I2. Solar cells employing this solid-state electrolyte have yielded solar to electrical energy conversion efficiencies of up to 2.6%. Electron-transfer kinetics were collected as a function of electrolyte composition, white light illumination, and device voltage and correlated with current/voltage characterization of the cell. The yield of electron injection from the dye excited state into the TiO2 electrode was found to be insensitive to electrolyte composition or cell operating conditions. Regeneration of the dye ground state by electron transfer from I- ions in the polymer electrolyte exhibited half times of 4−200 μs, depending upon the concentration of NaI in the polymer electrolyte. A long-lived product of the regeneration reaction was observed and assigned to the I2- radical. At...

Review of Layer Transfer Processes for Crystalline Thin-Film Silicon Solar Cells

Abstract: Layer transfer processes provide a new and largely unexplored route for the fabrication of highly efficient monocrystalline thin-film Si solar cells. Monocrystalline Si wafers serve as a substrate for epitaxial growth. A special surface conditioning of the substrate permits the transfer of a thin epitaxial film to an arbitrary carrier substrate. The growth substrate is then re-used to fabricate further cells. The possibility to use different materials for growing the thin film and for carrying the devices broadens the design flexibility and opens a new path for cost reduction. We describe and discuss the various layer transfer processes that are currently being developed for Si. A particular important point to work on in the future is the demonstration of a frequent re-use of the substrate and the development of a large-area and low-cost epitaxy technique.

Molecular photovoltaics that mimic photosynthesis

Abstract: Learning from the concepts used by green plants, we have developed a photo- voltaic cell based on molecular light absorbers and mesoporous electrodes. The sensitized nanocrystalline injection solar cell employs organic dyes or transition-metal complexes for spectral sensitization of oxide semiconductors, such as TiO 2, ZnO, SnO2, and Nb2O5. Mesoporous films of these materials are contacted with redox electrolytes, amorphous organ- ic hole conductors, or conducting polymers, as well as inorganic semiconductors. Light har- vesting occurs efficiently over the whole visible and near-IR range due to the very large inter- nal surface area of the films. Judicious molecular engineering allows the photoinduced charge separation to occur quantitatively within femtoseconds. The certified overall power conversion efficiency of the new solar cell for standard air mass 1.5 solar radiation stands presently between 10 and 11. The lecture will highlight recent progress in the development of solar cells for practical use. Advancement in the understanding of the factors that govern photovoltaic performance, as well as improvement of cell components to increase further its conversion efficiency will be discussed.

Nanoparticle Oxides Precursor Inks for Thin film Copper Indium Gallium Selenide (CIGS) Solar Cells

Abstract: The paper describes ISET’s patented non-vacuum process for low cost mass production of CIGS solar cells. In this process, the water based precursor inks of mixed oxides are deposited on various conducting substrates by a variety of non-vacuum coating techniques. The oxides are converted to CIGS by annealing and the device is completed by deposition of CdS by CBD followed by ZnO deposition by MOCVD. Small area solar cells with efficiency >13% have been fabricated by this process. The advantages of this non-vacuum process are: high compositional control of the absorber layer, high materials utilization and low cost.

Synthesis and Characterization of a Poly(1,3-dithienylisothianaphthene) Derivative for Bulk Heterojunction Photovoltaic Cells

Abstract: The synthesis of a poly(1,3-dithienylisothianaphthene) (PDTITN) derivative obtained via oxidative polymerization of 5,6-dichloro-1,2-bis(3'-dodecylthienyl)isothianaphthene is described. PDTITN exhibits a band gap of 1.80-1.85 eV. The redox properties of PDTITN were characterized using cyclic voltammetry and spectroelectrochemistry. Photoexcitation of PDTITN results in photoluminescence (PL) in the near-IR region and the formation of a triplet state. In the presence of a methanofullerene (PCBM) as an electron acceptor, PL and triplet formation of PDTITN are quenched. In photovoltaic devices using blends of the polymer with PCBM, the observed incident-photon-to-collected-electron efficiency (IPCE) up to 24% at 400 nm and the 3 orders of magnitude increase of short circuit current as compared to the polymer alone prove the photoactivity of the PDTITN/PCBM blend in the device.

Multi-junction solar cell device

Abstract: A multi-junction solar cell device (10) is provided. The multi-junction solar cell device (10) comprises either two or three active solar cells connected in series in a monolithic structure. The multi-junction device (10) comprises a bottom active cell (20) having a single-crystal silicon substrate base and an emitter layer (23). The multi-junction device (10) further comprises one or two subsequent active cells each having a base layer (32) and an emitter layer (23) with interconnecting tunnel junctions between each active cell. At least one layer that forms each of the top and middle active cells is composed of a single-crystal III-V semiconductor alloy that is substantially lattice-matched to the silicon substrate (22). The polarity of the active p-n junction cells is either p-on-n or n-on-p. The present invention further includes a method for substantially lattice matching single-crystal III-V semiconductor layers with the silicon substrate (22) by including boron and/or nitrogen in the chemical structure of these layers.

Crystalline Silicon Photovoltaic Cells

Abstract: The photovoltaic industry is in a phase of rapid expansion, growing at over 30 % per annum over recent years. Although technologies based on thin-film compound and alloy solar cells are under active development, most commercial solar cells presently use self-supporting bulk crystalline or multicrystalline silicon wafers, similar to those used in microelectronics. The laboratory performance of these cells, at 25 % solar energy conversion efficiency, is now approaching thermodynamic limits, with the challenge being to incorporate these improvements into low-cost commercial products. Improvements in cell optical design, particularly in their ability to “trap” weakly absorbed light, has also led to a growing interest in thin-film cells based on polycrystalline silicon, having advantages over other thin film photovoltaic candidates.

Photoinduced Electron Transfer in Donor−Acceptor Double-Cable Polymers: Polythiophene Bearing Tetracyanoanthraquinodimethane Moieties

Abstract: To circumvent the problems of morphology and donor−acceptor phase segregation in organic bulk heterojunction solar cells, double-cable materials, consisting of a hole conducting conjugated polymer chain carrying pendant electron accepting moieties, are proposed. We report the electrochemical synthesis of a double-cable material consisting of a polythiophene backbone with covalently bound tetracyanoanthraquinodimethane (TCAQ) moieties. Cyclic voltammetry and UV−vis absorption measurements reveal that in this functional material both the polythiophene chain and the TCAQ moieties maintain their individual electrochemical and electronic ground state properties. Photoinduced absorption (PIA) and light-induced electron spin resonance (LESR) studies clearly indicate photoinduced electron transfer from the polythiophene backbone to the TCAQ moieties upon photoexcitation. The results of the PIA are comparatively studied with UV/vis and near-infrared absorption spectra upon electrochemical doping.

Light-induced increase in the open-circuit voltage of thin-film heterogeneous silicon solar cells

Abstract: We observe a significant light-induced increase in open-circuit voltage, Voc, of solar cells whose intrinsic (i) layer consists of an amorphous and microcrystalline mixed phase The increase depends on the i-layer thickness and light-soaking intensity An increase of as large as 150 mV or 20% of the original Voc is observed The original Voc is restored after subsequent thermal annealing The possible mechanism for the Voc increase is discussed

Impurity photovoltaic effect in indium-doped silicon solar cells

Abstract: Impurity photovoltaic effect is investigated in two groups of indium-doped single-crystalline silicon solar cells with n-type and p-type dopants in the base layer. The continuity equation for minority carriers is solved numerically using the charge neutrality condition and current–voltage characteristics are found. It is shown that the improvement of short-circuit current due to carrier photogeneration from the deep defect level is negligible for both groups of the cells considered. Short-circuit current increases with increasing the trap concentration and open-circuit voltage abruptly decreases for trap concentrations close to compensation by n-type dopant. However, these dependencies occur due to the increase of lifetime, the decrease of the total equilibrium carrier density, and take place even in the absence of the absorption of subgap photons. It is shown that indium is not the proper impurity for efficiency improvements of silicon solar cells due to the impurity photovoltaic effect.

Thermodynamic theory of thermophotovoltaic solar energy conversion

Abstract: The thermophotovoltaic (TPV) efficiency is maximized by using three optimization parameters, namely, the absorber and PV solar cell temperatures and the voltage across the cell. Various combinations of spherical and (disk) plane absorbers and solar cells are analyzed. The best performance is associated with a combination plane absorber–plane solar cell. The thermal design has a significant influence on the optimum PV cell band gap. In the case of a normal thermal design, the cell temperature is usually high and depends strongly on the band gap. When a very good thermal design is considered, the optimum cell temperature is less than 30 degrees higher than the ambient temperature and decreases with an increase in the band gap. Increasing the ratio rA/rc between the absorber and PV cell radii leads to increased TPV efficiency. The optimum absorber temperature (practically) does not depend on rA/rc.

Sonochemical synthesis of crystalline nanoporous zinc oxide spheres and their application in dye‐sensitized solar cells

Abstract: A composite material made of zinc oxide and polyvinyl alcohol was prepared by a sonochemical method. Annealing of the composite under air removed the polymer, leaving porous spheres of ZnO. This change was accompanied by a change of the surface area from 2 m2/g to 34 m2/g. The porous ZnO particles were used as the electrode material for dye-sensitized solar cells (DSSCs). It was tested by forming a film of the doped porous ZnO on a conductive glass support. The performance of the solar cell is reported.

How do Buffer Layers Affect Solar Cell Performance and Solar Cell Stability

Abstract: Buffer layers are commonly used in the optimization of thin-film solar cells. For CuInSe2-and CdTe-based solar cells, multilayer transparent conductors (TCOs, e.g., ZnO or SnO2) are generally used in conjunction with a CdS heterojunction layer. Optimum cell performance is usually found when the TCO layer in contact with the CdS is very resistive or almost insulating. In addition to affecting the open-circuit voltage of a cell, it is commonly reported that buffer layers affect stress-induced degradation and transient phenomena in CdTe- and CuInSe2-based solar cells. In amorphous silicon solar cells, light-induced degradation has a recoverable and a nonrecoverable component too, and the details of the mechanism may depend on the p-type contact layer. Because of the similarity of transients and degradation in dissimilar material systems, it is suggested that degradation and recovery are driven by carriers rather than by diffusing atomic species. The question that must be addressed is why, not how, species diffuse and atomic configurations relax differently in the presence of excess carriers. In this paper, I suggest that the operating conditions of a cell can change the carrier transport properties. Often, excess carriers may enhance the conductance in localized regions (“filaments”) and buffer layers; limiting current flow into such filaments may therefore control the rate and amount of degradation (or recovery).