Polymer solar cells are reviewed in the context of the processing techniques leading to complete devices. A distinction is made between the film-forming techniques that are used currently such as ...spincoating, doctor blading and casting and the, from a processing point of view, more desirable film-forming techniques such as slot-die coating, gravure coating, knife-over-edge coating, off-set coating, spray coating and printing techniques such as ink jet printing, pad printing and screen printing. The former are used almost exclusively and are not suited for high-volume production whereas the latter are highly suited, but little explored in the context of polymer solar cells. A further distinction is made between printing and coating when a film is formed. The entire process leading to polymer solar cells is broken down into the individual steps and the available techniques and materials for each step are described with focus on the particular advantages and disadvantages associated with each case.
In this paper an overview of the development of organic photovoltaics is given, with emphasis on polymer-based solar cells. The observation of photoconductivity in solid anthracene in the beginning ...of the 19th century marked the start of this field. The first real investigations of photovoltaic (PV) devices came in the 1950s, where a number of organic dyes, particularly chlorophyll and related compounds, were studied. In the 1980s the first polymers (including poly(sulphur nitride) and polyacetylene) were investigated in PV cells. However, simple PV devices based on dyes or polymers yield limited power conversion efficiencies (PCE), typically well below 0.1%. A major breakthrough came in 1986 when Tang discovered that bringing a donor and an acceptor together in one cell could dramatically increase the PCE to 1%. This concept of heterojunction has since been widely exploited in a number of donor–acceptor cells, including dye/dye, polymer/dye, polymer/polymer and polymer/fullerene blends. Due to the high electron affinity of fullerene, polymer/fullerene blends have been subject to particular investigation during the past decade. Earlier problems in obtaining efficient charge carrier separation have been overcome and PCE of more than 3% have been reported. Different strategies have been used to gain better control over the morphology and further improve efficiency. Among these, covalent attachment of fullerenes to the polymer backbone, creating so-called double-cable polymers, is the latest. The improved PCE of plastic solar cells combined with increased (shelf and operating) lifetime, superior material properties and available manufacturing techniques may push plastic PVs to the market place within a few years.
A complete polymer solar cell module prepared in the ambient atmosphere using all-solution processing with no vacuum steps and full roll-to-roll (R2R) processing is presented. The modules comprise ...five layers that were prepared on a 175-μm flexible polyethyleneterephthalate (PET) substrate with an 80-nm layer of transparent conducting indium–tin oxide (ITO). The ITO layer was first patterned by screen printing an etch resist followed by etching. The second layer was applied by either knife-over-edge (KOE) coating or slot-die coating a solution of zinc oxide nanoparticles (ZnO-nps) followed by curing. The second layer comprised a mixture of the thermocleavable poly-(3-(2-methylhexan-2-yl)-oxy-carbonyldithiophene) (P3MHOCT) and ZnO-nps and was applied by a modified slot-die coating procedure, enabling slow coating speeds with low viscosity and low surface tension ink solutions. The third layer was patterned into stripes and juxtaposed with the ITO layer. The fourth layer comprised screen-printed or slot-die-coated PEDOT:PSS and the fifth and the final layer comprised a screen-printed or slot-die-coated silver electrode. The final module dimensions were 28
cm×32
cm and presented four individual solar cell modules: a single-stripe cell, a two-stripe serially connected module, a three-stripe serially connected module and finally an eight-stripe serially connected module. The length of the individual stripes was 25
cm and the width was 0.9
cm. With overlaps of the individual layers this gave a width of the active layer of 0.6
cm and an active area for each stripe of 15
cm
2. The performance was increased ten fold compared to mass-produced modules employing screen printing for all five layers of the device. The processing speeds employed for the R2R processed layers were in the range of 40–50
m
h
−1. Finally a comparison is made with the state of the art represented by P3HT–PCBM as the active layer and full R2R solution processing using slot-die coating.
Large-area solar cells (active area=3 and 10
cm
2) were prepared with low band gap polymers based on thiophene and benzothiadiazole (
1) or thiophene and benzo-bis(thiadiazole) (
2). The band gaps of ...the polymers were 1.65 and 0.67
eV, respectively. The best photovoltaic performance was obtained for the device ITO/PEDOT/
1:PCBM (1:2)/Al with an active area of 3
cm
2. The efficiency of the device was 0.62%. This is a high efficiency for a low band gap polymer in a large-area organic solar cell and thus polymer
1 is a very promising material for organic solar cells. The devices based on
2 were found to give poor devices when employed in bulk heterojunctions with PCBM. This was linked to a poor alignment of the energy levels in
2 with that of the electrodes and PCBM, showing that the requirement for a control of the positions of the energy levels becomes increasingly important as the band gap decreases.
Stability/degradation of polymer solar cells Jørgensen, Mikkel; Norrman, Kion; Krebs, Frederik C.
Solar energy materials and solar cells,
07/2008, Letnik:
92, Številka:
7
Journal Article
Recenzirano
Polymer and organic solar cells degrade during illumination and in the dark. This is in contrast to photovoltaics based on inorganic semiconductors such as silicon. Long operational lifetimes of ...solar cell devices are required in real-life application and the understanding and alleviation of the degradation phenomena are a prerequisite for successful application of this new and promising technology. In this review, the current understanding of stability/degradation in organic and polymer solar cell devices is presented and the methods for studying and elucidating degradation are discussed. Methods for enhancing the stability through the choice of better active materials, encapsulation, application of getter materials and UV-filters are also discussed.
Degradation mechanisms of a photovoltaic device with an Al/C
60/C
12-PSV/PEDOT:PSS/ITO/glass geometry was studied using a combination of in-plane physical and chemical analysis techniques: TOF-SIMS, ...AFM, SEM, interference microscopy and fluorescence microscopy. A comparison was made between a device being stored in darkness in air and a device that had been subjected to illumination under simulated sunlight (1000
W
m
–2, AM1.5) in air. It was found that oxygen diffuses through pinholes in the aluminium electrode. If stored in air in the dark the oxidation is limited to the C
60 layer. Illumination accelerates the oxidation/degradation and thus expands the process to involve at least the underlying layer of C
12-PSV. Furthermore, it was found that particles are formed in the device during storage.
In this work we study the degradation of roll-coated flexible inverted organic solar cells in different atmospheres. We demonstrate that impedance spectroscopy is a powerful tool for elucidating ...degradation mechanisms; it is used here to distinguish the different degradation mechanisms due to water and oxygen. Identical cells were exposed to different accelerated degradation environments using water only, oxygen only, and both water and oxygen simultaneously, all of them enhanced with UV light. The photocurrent is dramatically reduced in the oxygen-degraded samples. Impedance measurements indicate that this phenomenon is attributed to defects introduced by absorption of oxygen, which results in an increase of the acceptor impurity (NA) at the cathode interface obtained from a Mott-Schottky analysis. Simultaneously, at the anode interface where PEDOT:PSS is not shielded by the substrate, the nature of degradation differs for the water and oxygen degraded samples. While oxygen + UV light decreases the conductivity of the PEDOT:PSS layer, water + UV light changes the PEDOT:PSS work function inducing a depletion region at the anode.
•Degradation of low cost flexible organic solar cells exposed to degradation agents.•Impedance spectroscopy used to identify bulk and interfacial degradation mechanisms.•Oxygen increases the PEDOT:PSS layer resistivity in the oxygen degraded samples.•Water lowers the PEDOT:PSS work function in the water degraded samples.
This work attempts to reveal the comparability issues related to outdoor testing procedures of organic photovoltaic (OPV) modules via studies of inter-laboratory long-term outdoor measurements of ...roll-to-roll coated flexible OPV modules (P3HT:PCBM, inverted architecture) in different geographic locations from both Southern and Northern hemispheres. The interpretation of the module degradation via sub-cell analyses is presented and the poor reproducibility of the module performance linked to the barrier properties of the encapsulation around the device terminals is addressed. We demonstrate that the modules' t sub(80) lifetime may vary between a few hundred to over 10,000 h depending on how well the device terminals are sealed. We additionally demonstrate up to 17 months of stable performance for sub-cells within the modules. Furthermore, the effects of different geographical locations, weather conditions and measurement setups on the comparability of test results are analyzed. A strong link between the device temperature and performance is revealed, which is ascribed to the reaction of PEDOT:PSS layer with water. The estimation of the true performance of the modules by accommodation of variations in testing conditions is performed. Based on the results a set of recommendations from the ISOS-O guiding protocols are highlighted, which can help remove the factors that affect the comparability of the test results.
A complete polymer solar cell module prepared in the ambient atmosphere under industrial conditions is presented. The versatility of the polymer solar cell technology is demonstrated through the use ...of abstract forms for the active area, a flexible substrate, processing entirely from solution, complete processing in air using commonly available screen printing, and finally, simple mechanical encapsulation using a flexible packaging material and electrical contacting post-production using crimped contacts. We detail the production of more than 2000 modules in one production run and show that the production technique is scalable and well suited for direct transfer to the printing industry employing existing production equipment. The production speed and cost analysis for the individual modules from this batch is discussed and a forecast for the high volume cost based on this method is given. Further, the points where significant cost reductions can be achieved are identified. The use of the solar cell as the power supply for a small radio and other small electronic circuits is demonstrated. Lastly, the operational stability under ambient conditions in the dark and under illumination is discussed.
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