Organic photovoltaics has come into the international research focus during the past three years. Up to now main efforts have focused on the improvement of the solar conversion efficiency, and in ...recent efforts 5% white light efficiencies on the device level have been realized. Despite this in comparison to inorganic technologies low efficiency, organic photovoltaics is evaluated as one of the future key technologies opening up completely new applications and markets for photovoltaics. The key property which makes organic photovoltaics so attractive is the potential of reel to reel processing on low cost substrates with standard coating and printing processes. In this contribution we discuss the economical and technical production aspects for organic photovoltaics.
We investigate thin poly(3‐hexylthiophene‐2,5‐diyl)/6,6‐phenyl C61 butyric acid methyl ester (P3HT/PCBM) films, which are widely used as active layers in plastic solar cells. Their structural ...properties are studied by grazing‐incidence X‐ray diffraction (XRD). The size and the orientation of crystalline P3HT nanodomains within the films are determined. PCBM crystallites are not detected in thin films by XRD. Upon annealing, the P3HT crystallinity increases, leading to an increase in the optical absorption and spectral photocurrent in the low‐photon‐energy region. As a consequence, the efficiency of P3HT/PCBM solar cells is significantly increased. A direct relation between efficiency and P3HT crystallinity is demonstrated.
Structural properties of films of poly‐ 3‐hexylthiophene‐2,5‐diyl/6,6‐phenyl C61 butyric acid methyl ester (P3HT/PCBM) have been studied by X‐ray diffraction. P3HT crystallites with a‐axis orientation (see Figure) were observed, whereas PCBM crystallites were not found. The influence of P3HT crystallinity on the performance of P3HT/PCBM solar cells is discussed.
Organic photovoltaics (OPVs) are compatible with printing processes. We show that inkjet printing technology can be used for the fabrication of high‐ efficiency OPVs. The appropriate selection of ...organic solvent mixture creates an ultrasmooth inkjet printed active layer with intimate morphology and interfaces for efficient performance (see figure). We report 3% power‐ conversion‐efficiency organic solar cells with inkjet printed polymer: fullerene blend photoactive layer.
The transfer from poly-3hexylthiophene (P3HT) based fullerene free organic photovoltaic (OPV) lab cells with IDTBR (rhodanine-benzothiadiazole-coupled indacenodithiophene) as acceptor material to ...fully solution processed roll-to-roll (R2R) compatible modules is reported. The developed R2R process is fully compatible with industrial requirements as it uses exclusively non-hazardous solvents. The combination of optimized ink formulation, module layout, and processing affords efficiencies of 5% on 60 cm 2 total module area.
Plastic Solar Cells Brabec, C. J.; Sariciftci, N. S.; Hummelen, J. C.
Advanced functional materials,
02/2001, Letnik:
11, Številka:
1
Journal Article
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Recent developments in conjugated‐polymer‐based photovoltaic elements are reviewed. The photophysics of such photoactive devices is based on the photo‐induced charge transfer from donor‐type ...semiconducting conjugated polymers to acceptor‐type conjugated polymers or acceptor molecules such as Buckminsterfullerene, C60. This photo‐induced charge transfer is reversible, ultrafast (within 100 fs) with a quantum efficiency approaching unity, and the charge‐separated state is metastable (up to milliseconds at 80 K). Being similar to the first steps in natural photosynthesis, this photo‐induced electron transfer leads to a number of potentially interesting applications, which include sensitization of the photoconductivity and photovoltaic phenomena. Examples of photovoltaic architectures are presented and their potential in terrestrial solar energy conversion discussed. Recent progress in the realization of improved photovoltaic elements with 3 % power conversion efficiency is reported.
Recent developments in conjugated‐polymer‐based photovoltaic elements are reviewed here and an introduction to the underlying photophysics is given. Examples of photovoltaic architectures are presented and their potential in terrestrial solar energy conversion is discussed. The Figure shows a large‐area plastic solar cell running a small motor. (See also inside front cover.)
Photovoltaic installations will likely become one of the major power sources in the 21st century and we need photovoltaic modules to operate reliably. In this review, we explore what is known today ...about the status of installed crystalline silicon photovoltaic modules in the world, how different sources classify module defects, and what we might deduce for future installations. Looking at more than 200 results from 132 installations and 79 reports, we find that PV modules in general are robust in outdoor operation, with about one in 250 modules failing completely each year. About one in ten modules will develop a defect resulting in greater than expected power loss throughout their lifetime, and practically every module will develop visually perceivable alterations. We observe no trends of changes over time in these findings, hence there is no indication that future performance will deviate dramatically. We note though that more information is needed. Available studies represent a module fleet with greater age than current installations, and are over-representing multicrystalline - compared to monocrystalline silicon, and AL-BSF - compared to PERC cell architectures. Studies from Asia and Africa and from tropical climates are underrepresented. A major challenge in the analysis was the variety of metrics used. To facilitate easier comparison, we propose reporting guidelines.
Photovoltaic installations will likely become one of the major power sources in the 21st century and we need photovoltaic modules to operate reliably. The map shows the average photovoltaic fleet age in Europe.
A series of highly soluble fullerene derivatives with varying acceptor strengths (i.e., first reduction potentials) was synthesized and used as electron acceptors in plastic solar cells. These ...fullerene derivatives, methanofullerene 6,6‐phenyl C61‐butyric acid methyl ester (PCBM), a new azafulleroid, and a ketolactam quasifullerene, show a variation of almost 200 mV in their first reduction potential. The open circuit voltage of the corresponding devices was found to correlate directly with the acceptor strength of the fullerenes, whereas it was rather insensitive to variations of the work function of the negative electrode. These observations are discussed within the concept of Fermi level pinning between fullerenes and metals via surface charges.
A variation of almost 200 mV has been found for the first reduction potential of a series of highly soluble fullerene derivatives with varying acceptor strengths that were used as electron acceptors in plastic solar cells. This observation, which also relates the open circuit voltage to the acceptor strengths, is discussed within the concept of Fermi level pinning between fullerenes and metals. The Figure shows an azafulleroid that was used in this investigation.
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•A real-size prototype of the CPC PVT flat plate collector was built and tested.•The components and the construction of the collector is described.•The results of the thermal and PV ...efficiency of the collector are presented.•Further, the incidence angle modifier for thermal and PV efficiency has been measured.
PVT collectors aim to solar co-generation of electricity and heat. An new concept raises thermal efficiency by concentrating sunlight with CPC reflectors, in order to access a higher number of solar thermal applications. Losses in PV efficiency due to a higher operating temperature are accepted with regard to a higher overall collector efficiency. As a side effect, the concentration lowers the material usage of PV and enables a high efficient thermal coupling of the PV cell to the heat carrying fluid.
The work focuses on the construction, as well as on the angle dependent electrical and thermal measurement of the real-size CPC PVT collector prototype (1460mm×600mm×150mm). In previous publications, calculations and experiments studied the influence of the CPC reflectors on the PV efficiency. Further, the thermal coupling between PV cell and heat carrier fluid has been measured in a lab experiment. These results, together with transient annual simulations, were considered in the design process of the CPC PVT prototype with an angular acceptance range of ±25°.
The experiments were conducted on the outdoor solar test facility at ZAE Bayern in Garching, Germany. The thermal and PV efficiency has been measured with MPP tracking, as well as for open circuit voltage for fluid temperatures up to 107°C.
It could be shown, that the thermal efficiency while MPP tracking is elevated to 34% compared to a glazed flat plate PVT with 17% for collector temperatures 60K over ambiance. At the same time, the electrical efficiency drops from 15% cell efficiency to an overall collector efficiency of 9%, due to the optical setup, temperature effects and a non-uniform flux distribution caused by the reflectors.
In this paper we report on printed bulk heterojunction solar cells from poly(3‐hexylthiophene) (P3HT) and 6,6‐phenyl C61 butyric acid methyl ester (PCBM) with power efficiencies of over 4 %. Devices ...have been produced by doctor blading, which is a reel‐to‐reel compatible large‐area coating technique. Devices exhibit a short‐circuit current of over 11.5 mA cm–2, a fill factor of 58 %, and an open‐circuit voltage of 615 mV, resulting in an AM1.5 power efficiency of over 4.0 % at 25 °C and under 100 mW cm–2. The mismatch factor of the solar simulator is cross‐calibrated by determining the spectral quantum efficiency of organic devices as well as of a calibrated Si device, and by the combination of outdoor tests; these efficiencies are precise within less than 3 % relative variation. Although the devices are regarded as fairly optimized, analysis in terms of a one‐diode equivalent circuit reveals residual losses and loss mechanisms. Most interestingly, the analysis points out the different properties of spin‐coated versus bladed devices. Based on this analysis, the future efficiency potential of P3HT–PCBM solar cells is analyzed.
Printed bulk heterojunction solar cells from poly(3‐hexylthiophene) and a methanofullerene with power efficiencies of over 4 % are reported (see figure). Though these devices appear fairly optimized, analysis on the basis of a one‐diode equivalent circuit reveals residual open‐circuit voltage losses as well as fill‐factor losses. Imperfections in the bulk distribution of the nanometer‐scaled donor–acceptor heterojunctions are suggested as the origin for the residual losses.
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