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A comprehensive outdoor study of polymer solar cells and modules for duration of one year was conducted. Different sample geometries and encapsulations were employed in order to study the spread in the lifetimes. The study is a complimentary report to previous work that focused on indoor ageing tests. Comparison of the indoor and outdoor lifetimes was performed by means of the o-diagram, which constitutes the initial steps towards establishing a method for predicting the lifetime of an organic photovoltaic device under real operational conditions based on a selection of accelerated indoor tests. Acceleration factors were determined using the ISOS-protocols, which enabled reproducible data acquisition between different laboratories and operators within the OPV community. A semi-automatic filtering method was employed for processing data acquired in outdoor tests. It was found that the lifetime of the samples tested under outdoor conditions was somewhere between the lifetimes of samples measured in accelerated indoor test conditions of damp heat and light soaking (ISOS-D-3 and ISOS-L-2) and in moderate indoor test conditions (shelf life and high temperature storage). The presented results reveal that while the accelerated ageing studies reveal days and weeks of lifetime for the studied samples, in outdoor real operational conditions the samples demonstrate stability up to months and seasons. [ABSTRACT FROM AUTHOR]

Abstract: The polymer and organic solar cell technology is critically presented in the context of other thin film technologies with a specific focus on what it will take to make them a commercial success. The academic success of polymer and organic solar cells far outweigh any other solar cell technology when judging by the number of scientific publications whereas the application of polymer and organic solar cells in real products is completely lacking. This aspect is viewed as a sign of the polymer and organic solar cell field as being more complex and less mature and it raises the question of whether an organic analog to a successful inorganic technology is forcibly needed and indeed whether it is at all worth exploring beyond academia. [Copyright &y& Elsevier]

Abstract: A simple and low cost thin film solution processing system comprising a single roll coating machine has been developed to allow direct investigation of variable parameter effects in roll-to-roll processing. We present roll coating of the active layers in polymer solar cells and validate the instrument by reinvestigating the well known effect of solvent on performance. We obtained a maximum power conversion efficiency of 1.6% for the reference cells, which compares well with reported roll-to-roll coated cells according to ProcessOne, with a relative deviation caused by solvent type nearing 40% on roll coated cells, confirming the solvent to have a significant influence on the performance of the finished cell. We further present a slot-die coating head with an ultra low dead volume allowing for the preparation of roll coated polymer solar cells on flexible substrates with nearly no loss of solution, enabling roll coating testing of new polymers where only small amounts are often available. We demonstrate the formation of >50 solar cells (each with an active area of 1cm2) with printed metal back electrodes using as little as 0.1mL of active layer solution. This approach outperforms spin coating with respect to temperature control, ink usage, speed and is directly compatible with industrial processing and upscaling. [Copyright &y& Elsevier]

Abstract: We applied complementary imaging methods to investigate processing failures of roll-to-roll solution processed polymer solar modules based on polymer:fullerene bulk heterojunctions. For investigation of processing deficiencies in solar modules we employed dark lock-in thermography (DLIT), electroluminescence (ELI) and photoluminescence/reflection imaging (PLI/RI) complemented by optical imaging (OI). The combination of all high resolution images allowed us to allocate the origin of processing errors to a specific deposition process, i.e. the insufficient coverage of an electrode interlayer. The investigation can be divided into a fast DLIT overview of the module and a successive more detailed analysis of the suspicious region by all imaging methods. [Copyright &y& Elsevier]

Abstract: The performance of printable metal back electrodes for polymer solar cells were investigated using light beam induced current (LBIC) mapping of the final solar cell device after preparation to identify the causes of poor performance. Three different types of silver based printable metal inks were employed. Organic solvent based, UV-curable and water based silver inks were tested. Both grid electrodes and full electrodes were employed and it was shown via the grid electrode that the organic solvent based ink adversely affects the device performance under the printed metal whereas both the UV-curable and the water based inks were neutral to improving device performance. Complete roll-to-roll (R2R) processed modules were also tested and some limitations of the LBIC technique was identified for serially connected modules. [Copyright &y& Elsevier]

Abstract: A round robin for the performance of roll-to-roll coated flexible large-area polymer solar-cell modules involving 18 different laboratories in Northern America, Europe and Middle East is presented. The study involved the performance measurement of the devices at one location (Risø DTU) followed by transportation to a participating laboratory for performance measurement and return to the starting location (Risø DTU) for re-measurement of the performance. It was found possible to package polymer solar-cell modules using a flexible plastic barrier material in such a manner that degradation of the devices played a relatively small role in the experiment that has taken place over 4 months. The method of transportation followed both air-mail and surface-mail paths. [Copyright &y& Elsevier]

Abstract: A roll-to-roll process for polymer solar cells that does not involve indium-tin-oxide (ITO) is presented. A commercially available kapton foil with an overlayer of copper was used as the substrate. Sputtering of titanium metal onto the kapton/copper in an R2R vacuum process gave the monolithic substrate and back electrode for the devices. The active layer was slot-die coated onto the kapton/Cu/Ti foil followed by slot-die coating of a layer of PEDOT:PSS. No patterning of the first four layers was necessary and only the final front electrode required a pattern. The front electrode was applied by screen printing a protective layer in the areas for front electrode contacts and finally a silver grid was applied by screen printing. The topology of the device and the choice of final grid electrode geometry allowed for serial connection of the individual cells into modules. The individual cells were as large as 150×150mm. The geometric fill factors were as high as 74% and thus much higher than is readily achieved using serially connected cells on the same substrate. [Copyright &y& Elsevier]

Abstract: A roll-to-roll process enabling fabrication of polymer solar cells comprising five layers on flexible substrates is presented. The device geometry is inverted and allow for fabrication on both transparent and non-transparent flexible substrates. The process is illustrated in this work by formation of a bottom electrode comprising silver nanoparticles on a 130 micron thick polyethyleneternaphthalate (PEN) substrate. Subsequently an electron transporting layer of zinc oxide nanoparticles was applied from solution followed by an active layer of P3HT-PCBM and a hole transporting layer of PEDOT:PSS. These first four layers were applied by slot-die coating. The final electrode was applied by screen printing a grid structure that allowed for transmission of 80% of the light. The materials were patterned into stripes allowing for formation of a single cell device and serially connected modules comprising 2, 3 and 8 stripes. All five layers in the device were processed from solution in air and no vacuum steps were employed. An additional advantage is that the use of indium-tin-oxide (ITO) is avoided in this process. The devices were tested under simulated sunlight (1000Wm−2, AM1.5G) and gave a typical performance 0.3% in terms of power conversion efficiency (PCE) for the active layer. The low PCE was due to poor transmission of light through the back electrode. [Copyright &y& Elsevier]

Abstract: Pad printing as a technique for preparing the active layer in polymer solar cells is presented. The technique employs a silicone rubber stamp to pick up the motif from a gravure plate and transfer it to the substrate. The strengths and limitations of pad printing are discussed and polymer solar cells prepared by pad printing are presented. Devices were prepared on indium tin oxide substrates but in principle the entire photovoltaic device comprising front and back electrodes, barrier layers and active layer could be printed with no need for vacuum steps. The device geometry comprises a spin coated transparent zinc oxide front electrode, a pad printed active layer based on a bulk heterojunction of the thermocleavable polymer poly(3-(2-methylhexyloxycarbonyl)thiophene-co-thiopene) (P3MHOCT) and zinc oxide nanoparticles, spin coated PEDOT:PSS and finally a manually cast thermally cured silver paste back electrode. The P3MHOCT was converted to poly(3-carboxy-dithiophene) (P3CT) in situ by heating the film to for a brief period. The entire printing and device preparation was carried out in the ambient atmosphere and the devices obtained had a good stability in air during storage and operation. [Copyright &y& Elsevier]

Abstract: 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 28cm×32cm 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 25cm and the width was 0.9cm. With overlaps of the individual layers this gave a width of the active layer of 0.6cm and an active area for each stripe of 15cm2. 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 40–50mh−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. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: In this paper we present the realization of extremely thin absorber (ETA) solar cells employing conductive glass substrates functionalized with TiO2 microstructures produced by embossing. Nanocrystalline or compact TiO2 films on Indium doped tin oxide (ITO) glass substrates were embossed by pressing a silicon stamp containing a μm size raised grid structure into the TiO2 by use of a hydraulic press (1ton/50cm2). The performance of these microstructured substrates in a ETA cell sensitized by a thermally evaporated or chemical bath deposited PbS film and completed by a PEDOT:PSS hole conductor layer and a Au counter electrode is compared to that of planar substrates. Surprisingly planar films produced better performance than micro-structured films. A simple model implying photoconductive shunting paths revealed by junction breakdown at negative bias under illumination is presented. [Copyright &y& Elsevier]

Abstract: Preliminary data on the fabrication of 0.1m2 polymer solar cells are presented. The process employed screen-printing of an active layer onto an indium-tin-oxide (ITO) electrode pattern (50Ωsquare−1) on a 200μm polyethyleneterphthalate (PET) substrate. After the printing, vacuum coating of an optional layer of C60 and the final aluminium electrode was employed to complete the device. The active layer consisted of poly-1,4-(2-methoxy-5-ethylhexyloxy)phenylenevinylene (MEH-PPV). Chlorobenzene was used as solvent for the screen-printing process. The design of the solar cell module was chosen to employ both serial and parallel connection of individual solar cells. Thirteen individual solar cells with an active area of 7.2cm2 were thus connected in series. The serial connection was chosen to reduce the current density for the large area employed. A step up in voltage is thus preferable to avoid resistive loss. The parallel connection of seven such rows through a screen-printed silver bus gave a solar cell module measuring 40cm×25cm (0.1m2). The active area was 65% of the total area. The remaining 35% of the area was used for interconnections between cells and for the separation between rows. The 65% active area was chosen to encompass a good margin for prototyping/research and to keep contact resistances between the cells low. In a fully automated process the active area could perhaps reach 90–99% interval but problems with current extraction and interconnections were found to become very critical. There are obvious shortcomings to this approach but the advantage of low current density is believed to be the biggest problem in efficient energy extraction from the module when no simple method for reducing the sheet resistance is available. In the simple geometry ITO/MEH-PPV/aluminium the module gave an open circuit voltage (V oc) of 10.5V, a short circuit current (I sc) of 5μA, a fill factor (FF) of 13% and an efficiency (η) of 0.00001% under AM1.5 illumination with an incident light intensity of 1000Wm−2. A geometry employing a sublimed layer of C60 (ITO/MEH-PPV/C60/Al) improved V oc, I sc, FF and η to 3.6V, 178μA, 19% and 0.0002%, respectively. The lifetimes (τ ½) of the devices defined as the time it takes for the module efficiency to attain half of its maximum value were found to improve significantly when a sublimed layer of C60 was included between the polymer and the aluminium electrode. The modules were laminated with 200μm polyethyleneterephthalate (PET) foil to mechanically protect the cells. τ ½ values of 150h were typically obtained. This short lifetime is linked to reaction between the reactive metal electrode (aluminium) and the constituents of the active layer. The modules were tested outdoors in different weather condition (wind, high temperature excursion, rain, snow). Tested during a storm the polymer photovoltaic laminate was subject to vibration stress and deformation and delamination in the organic layer was observed with fast bleaching of the active material. Efficient encapsulation with barriers that has very low oxygen and water permeabilities will be needed before future commercialisation can be anticipated. [Copyright &y& Elsevier]

Abstract: New carboxy-terpyridines selectively functionalized at the 4-, 4′- and 4″-positions were prepared in a three-step procedure with good yields using the Kröhnke reaction followed by saponification. Their complexation with ruthenium led to symmetric and unsymmetric terpyridinyl zwitterionic complexes. [Copyright &y& Elsevier]

Abstract: The incorporation of polymer photovoltaics into textiles was demonstrated following two different strategies. Simple incorporation of a polyethyleneterphthalate (PET) substrate carrying the polymer photovoltaic device prepared by a doctor blade technique necessitated the use of the photovoltaic device as a structural element. The total area of the device on PET was typically much smaller than the active area due to the decorative design of the aluminium electrode. Elaborate integration of the photovoltaic device into the textile material involved the lamination of a polyethylene (PE) film onto a suitably transparent textile material that was used as substrate. Plasma treatment of the PE-surface allowed the application of a PEDOT electrode that exhibited good adherence. Screen printing of a designed pattern of poly 1,4-(2-methoxy-5-(2-ethylhexyloxy))phenylenevinylene (MEH-PPV) from chlorobenzene solution and final evaporation of an aluminium electrode completed the device. The total area of the textile device was 1000cm2 (25cm×40cm) while the active area (190cm2) was considerably smaller due to the decorative choice of the active material. [Copyright &y& Elsevier]

Abstract: Transparent electrodes based on PEDOT were prepared using a variety of techniques suitable for large area applications from 3,4-ethylenedioxythiophene (EDT) and Fe(III)-tosylate. High conductivities were obtained (∼20Ω−1) with moderate transmission in the UV-visible range 350–600nm. We subsequently demonstrate the application of PEDOT electrodes to flexible polyethyleneterphthalate plastic substrates (PET) prepared by this procedure for polymer photovoltaic devices with active areas of 4.2cm2 using a 1:4 w/w mixture of MEHPPV and PCBM. We obtain typical efficiencies of 0.2% under simulated sunlight (AM1.5 at 1000Wm−2). [Copyright &y& Elsevier]

Abstract: The synthesis of a zwitterionic ruthenium dye that binds to anatase surfaces and has a built-in functionality that allows for the attachment of a conjugated polymer chain is presented. The system was found to adsorb on the surface of anatase anchored by the ruthenium dye. Two types of devices were prepared: standard photoelectrochemical (PEC) solar cells and polymer solar cells. The PEC solar cells employed a sandwich geometry between TiO2 nanoporous photoanodes and Pt counter electrodes using LiI/I2 in CH3CN as an electrolyte. The polymer solar cells employed planar anatase electrodes and the complex was adsorbed onto the surface before evaporation of gold electrodes. Alternative devices were obtained by spincoating of the polymer solution onto PEDOT:PSS covered indium-doped tin oxide substrates. PEC solar cells gave the best results and the main finding was that the polymer chain served as a light harvesting antenna for the ruthenium dye. [Copyright &y& Elsevier]

Abstract: We present the synthesis of oligohexylthiophenes starting from 3, 4′-dihexyl-[2, 2′]bithiophene (1) 3, 4′, 4″, 4‴-tetrahexyl-[2, 2′; 5′, 2″; 5″, 2‴]quarterthiophene (2), 3, 4′, 4″, 4‴, 4⁗, 4′′′′′, 4′′′′′′, 4′′′′′′′-octahexyl-[2, 2′; 5′, 2″; 5″, 2‴; 5‴, 2⁗; 5⁗, 2′′′′′; 5′′′′′, 2′′′′′′; 5′′′′′′, 2′′′′′′′]octithiophene (3) and 3, 4′, 4″, 4‴, 4⁗, 4′′′′′, 4′′′′′′, 4′′′′′′′, 4′′′′′′′′, 4′′′′′′′′′, 4′′′′′′′′′′, 4′′′′′′′′′′′, 4′′′′′′′′′′′′, 4′′′′′′′′′′′′′, 4′′′′′′′′′′′′′′, 4′′′′′′′′′′′′′′′-hexadecahexyl-[2, 2′; 5′, 2″; 5″, 2‴; 5‴, 2⁗; 5⁗, 2′′′′′; 5′′′′′, 2′′′′′′; 5′′′′′′, 2′′′′′′′; 5′′′′′′′, 2′′′′′′′′; 5′′′′′′′′, 2′′′′′′′′′; 5′′′′′′′′′, 2′′′′′′′′′′; 5′′′′′′′′′′, 2′′′′′′′′′′′; 5′′′′′′′′′′′, 2′′′′′′′′′′′′; 5′′′′′′′′′′′′, 2′′′′′′′′′′′′′; 5′′′′′′′′′′′′′, 2′′′′′′′′′′′′′′; 5′′′′′′′′′′′′′′, 2′′′′′′′′′′′′′′′]hexadecathiophene (4) by regioselective bromination using N-bromosuccinimide and regioselective lithiation using lithiumdiisopropylamide in ethylbenzene/THF/heptane followed by reaction with trimethylstannylchloride and subsequent palladium catalysed Stille coupling. We further synthesised 5,15-bis(3, 4′, 4″, 4‴, 4⁗, 4′′′′′, 4′′′′′′, 4′′′′′′′-octahexyl-[2, 2′; 5′, 2″; 5″, 2‴; 5‴, 2⁗; 5⁗, 2′′′′′; 5′′′′′, 2′′′′′′; 5′′′′′′, 2′′′′′′′]octithiophene-5-yl)-10, 20-bis(3, 5-ditertbutylphenyl)zinc(II)porphyrin (5) from trimethyl(3, 4′, 4″, 4‴, 4⁗, 4′′′′′, 4′′′′′′, 4′′′′′′′-Octahexyl-[2, 2′; 5′, 2″; 5″; 2‴; 5‴, 2⁗; 5⁗, 2′′′′′; 5′′′′′, 2′′′′′′; 5′′′′′′, 2′′′′′′′]octithiophene-5-yl)stannane (3-SnMe3 ) and 5, 15-dibromo-10, 20-bis(3, 5-ditertbutylphenyl)zinc(II)porphyrin (6) by Stille coupling. All the products were characterised by size exclusion chromatography (SEC), NMR, MALDI-TOF and elemental analysis and purified by preparative SEC before subjecting them to photophysical studies. UV–vis and emission spectroscopy were used to determine quantum yields and energy transfer. The photon balance was established and used to rationalise the photovoltaic behaviour of 4 and 5. While 4 gave rise to photovoltaic devices giving a moderate photovoltaic response that was symbatic with the absorption spectrum, 5 showed a photovoltaic response that was antibatic with a part of the absorption spectrum of the zinc-porphyrin constituent. We ascribe this behaviour to efficient internal conversion of the energy absorbed by (and the energy transferred to) the zinc-porphyrin constituent. [Copyright &y& Elsevier]

The possibility of making large area (100 cm2) polymer solar cells based on the conjugated polymer poly 1,4-(2-methoxy-5-ethylhexyloxy)phenylenevinylene (MEH-PPV) was demonstrated. Devices were prepared by etching an electrode pattern on ITO covered polyethyleneterephthalate (PET) substrates. A pattern of conducting silver epoxy allowing for electrical contacts to the device was silk screen printed and hardened. Subsequently a pattern of MEH-PPV was silk screen printed in registry with the ITO electrode pattern on top of the substrate. Final evaporation of an aluminum electrode or sublimation of a Buckminsterfullerene (C60) layer followed by an aluminum electrode completed the device. The typical efficiency of the prototype devices consisting of three solar cells in series were 0.0046% (under AM1.5 conditions) with open-circuit voltages (Voc) of 0.73 V and short-circuit currents (Isc) of 20 μA cm-2. The half-life based on Isc in air for the devices were 63 h. The cells were laminated in a 125 μm PET encasement. Lamination had a negative effect on the lifetime.We demonstrate the feasibility of industrial production of large area solar cells (1 m2) by silk screen printing and envisage the possibility of production volumes 10000 m2 h-1 at a cost that is on the order of 100 times lower than that of the established monocrystalline silicon solar cells in terms of materials cost. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

Abstract: In order to improve the accuracy, validity, reliability and reproducibility of reported power conversion efficiencies for solar cells, the journal, Solar Energy Materials and Solar Cells (SOLMAT), wishes to define how power conversion efficiencies should be reported. This expands upon what is specified in our Guide for Authors. This editorial also serves as a guide on how efficiency data should be checked within the reporting laboratory before sending cells or materials for testing at an independent laboratory. The threshold where the accuracy of efficiency values is important to the journal is whenever power conversion efficiencies require external quantum efficiencies (EQE) values above 50% over a large range of wavelengths or when reported power conversion efficiencies exceed 2.5%. Extra care should be taken in submitted manuscripts to document the measurement''s quality, relevance and independent verification. [Copyright &y& Elsevier]

Organic/polymer PV is a promising technology that could result in low cost flexible large area solar cells. The technology is typically presented as a thin film of a light absorbing conjugated organic/polymer material sandwiched between a transparent electrode and a metal electrode. Dr Frederik C. Krebs, Risø National Laboratory, Denmark reports on this potential alternative to traditional solar PV materials constructed from inorganic semi-conducting materials. [Copyright &y& Elsevier]

Abstract: In this study, we demonstrate fully solution processed semi-transparent silver electrodes on flexible substrates having a sheet resistance as low as 5Ω/□ and transmittance of ∼30% at 550nm. We demonstrate the use of this electrode as a substitute for ITO in an inverted organic solar cell (OSC) with the layer sequence, PET/Ag/ZnO/P3HT:PCBM/PEDOT:PSS/Ag where illumination is achieved through the first Ag layer. Power conversion efficiency of up to 1.6% under 1 sun illumination (100mWcm−2 and AM1.5G) is achieved for small area (1cm2) test devices. We further demonstrate scalability of the semi-transparent Ag electrode fabrication in a roll-to-roll (R2R) process using slot-die coating. This electrode is further utilized in R2R processing of large area modules (active area 35.5cm2) where all layers in the modules are R2R processed with solution-based materials in ambient conditions without any use of vacuum steps. We further demonstrate the possibility of using barrier foil as the substrate in the R2R processing of modules. Module performance is evaluated by current–voltage characterization and Light Beam Induced Current (LBIC imaging). Such a semi-transparent Ag electrode incurs very little material and processing cost and is a cost-effective alternative to ITO for low-cost organic solar cells. [Copyright &y& Elsevier]

Abstract: The interlayer adhesion of roll-to-roll processed flexible inverted P3HT:PCBM bulk heterojunction (BHJ) polymer solar cells is reported. Poor adhesion between adjacent layers may result in loss of device performance from delamination driven by the thermomechanical stresses in the device. We demonstrate how a thin-film adhesion technique can be applied to flexible organic solar cells to obtain quantitative adhesion values. For the P3HT:PCBM-based BHJ polymer solar cells, the interface of the BHJ with the conductive polymer layer PEDOT:PSS was found to be the weakest. The adhesion fracture energy varied from 1.6J/m2 to 0.1J/m2 depending on the composition of the P3HT:PCBM layer. Post-deposition annealing time and temperature were shown to increase the adhesion at this interface. Additionally the PEDOT:PSS cells are compared with V2O5 cells whereby adhesive failure marked by high fracture energies was observed. [Copyright &y& Elsevier]

Abstract: A controlled atmosphere setup designed for long-term degradation studies of organic solar cells under illumination is presented. The setup was designed with ease-of-use and compactness in mind and allows for multiple solar cells distributed on four glass substrates to be studied in four different chambers with temperature and atmosphere control. The four chambers are situated at close proximity in the setup thereby allowing the solar cells to be subjected to as uniform an illumination distribution as possible for the given solar simulator employed. The cell substrates serve as the front window and present a tight seal. Hence no illumination correction needs to be performed due to transmission and reflection losses as otherwise seen with test chambers employing a window as a seal. The solar cells in each chamber are continuously and individually electrically monitored under biased conditions by means of a computer controlled multiplexer and source meter. The dimensions of the setup allow it to pass through a mid-size load lock in most common glove box systems allowing for mounting of tested samples under inert conditions. As a demonstration of the applicability of the chamber design, a degradation study of standard P3HT:PCBM solar cells was performed under four different environmental conditions. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: A detailed description of a setup for studying ageing of polymer devices is presented. The system offers individual control of the environmental factors (oxygen, humidity, atmosphere, temperature and light intensity) causing the degradation of organic devices. The system was developed for accurate control of the conditions and data collection of photovoltaic (PV) parameters for organic solar cells during long-term testing. The atmosphere chamber can operate under vacuum conditions without temperature control. It is designed for operation at an internal gas pressure of around 1atm. It is further equipped for isotopic labeling experiments of the internal atmosphere (18O2 and H2 18O) such that degradation mechanisms can be studied using TOF-SIMS as a chemical probe. Experiments on both “accelerated” (by applying thermal stress to the devices) and “long-term” lifetime measurements of traditional organic bulk heterojunction solar cell devices have been realized while controlling the environmental conditions. As an example of use of the setup we determined the acceleration factor for standard bulk heterojunction devices based on ITO/PEDOT:PSS/P3HT-[60]PCBM/Al when operated under an ambient atmosphere and under an inert atmosphere at temperatures of 25, 43, 63 and 83°C. Different values for the acceleration factor were found depending on the atmosphere used and further our results suggest that the acceleration factor may change in time as different degradation mechanisms may dominate at different times during the device life. [Copyright &y& Elsevier]

Abstract: We report on the incorporation of a low band gap copolymer based on thiophene and benzothiadiazole with a band gap of 1.65eV into a bulk heterojunction device with the structure ITO/PEDOT:PSS/polymer:PCBM/Al. We have investigated the effects of process variable, including choice of solvent, polymer concentration and annealing temperature, on the photovoltaic device performance. The devices show spectral response down to the absorption edge of 1.65eV and exhibit an efficiency of 1% under AM1.5 illumination and a peak external quantum efficiency of 18% at 600nm. [Copyright &y& Elsevier]

Abstract: In this paper we present an attempt to substitute liquid electrolyte (LC) dye-sensitized solar cells (DSSCs) by quasi-solid-state constructions (SC) for semi-transparency application adopting organic/inorganic gels in combination with standard (Pt based) and alternative (PEDOT:PSS based) counter electrodes. Gel polymer electrolytes are prepared by incorporating a liquid electrolyte into a polymer matrix such as polymethyl-methacrylate (PMMA) using propylene carbonate (PC) as gelling solvent. SC employing gel electrolytes with a high content in PC have been shown to exhibit increased lifetime up to 70h under A.M. 1.5 irradiation. Counter electrodes were prepared by an airbrushing and tape casting technique of Pt salt solutions or by spin coating of commercial PEDOT:PSS solution. PEDOT:PSS counter electrodes were found to show similar I3 −/I− catalytic activities to Pt based counter electrodes and the best SC obtained gave a short circuit current of 2mAcm−2 and a open circuit voltage of 625mV. [Copyright &y& Elsevier]

The ability of printed organic solar cells (OSCs) to survive repeated mechanical deformation is critical to large-scale implementation. This paper reports an investigation into the mechanical stability of OSCs through bending and torsion testing of whole printed modules. Two types of modules are used that differ slightly in thickness as well as on the basis of the electrode materials: silver nanowires or carbon-based inks. Each type of module is subjected to two different mechanical modes of deformation, bending and torsion, of several thousand cycles per module using a purpose-built robotic device. Analysis of the distribution of stress in the devices performed by finite-element modeling predicts the locations of failure. Failure upon bending originates at the laser-cut edges of the modules from shear at the clamp/module interface leading to crazing of the plastic barrier encapsulant foils. This crazing leads to eventual delamination due first to decohesion of the active layer at the edge of the modules and later to deadhesion between the PEDOT:PSS (electrode) and P3HT:PCBM (semiconductor) layers. The torsion mode imposes greater stresses than the bending mode and thus leads to failure at fewer strain cycles. Failure during torsion occurs through crack propagation initiated at stress concentrations on the edges of the module that were imposed by their rectangular geometry and ultimately leads to bifurcation of the entire module. Rather than the differences in electrode materials, the differences in survivability between the two types of modules are attributed mostly to the thickness of the substrate materials used, with the thinner substrate used in the carbon-based modules (~160 µm) failing at fewer strain cycles than the substrate used in the silver-nanowire-based modules (~190 µm). Taken together, the results suggest ways in which the lifetimes of devices can be extended by the layouts of modules and choices of materials. [ABSTRACT FROM AUTHOR]

The challenge of preparing cross sections of organic photovoltaics (OPV) suitable for transmission electron microscopy (TEM) and scanning TEM (STEM) is addressed. The samples were polymer solar cells fabricated using roll-to-roll (R2R) processing methods on a flexible polyethylene terephthalate (PET) substrate. Focused ion beam (FIB) and ultramicrotomy were used to prepare the cross sections. The differences between the samples prepared by ultramicrotomy and FIB are addressed, focusing on the advantages and disadvantages of each technique. The sample prepared by ultramicrotomy yielded good resolution, enabling further studies of phase separation of P3HT:PCBM by means of energy filtered TEM (EFTEM). The sample prepared by FIB shows good structure preservation, but reduced resolution due to non-optimal thicknesses achieved after treatment. Degradation studies of samples prepared by ultramicrotomy are further discussed, which reveal particular effects of the ISOS-L-3 aging test (85 °C, 50% R.H., 0.7 Sun) onto the sample, especially pronounced in the silver layer. [ABSTRACT FROM AUTHOR]

We investigated the response of roll coated organic solar cells at different bias voltages and illumination levels to implement a detailed impedance model. The technique used for the investigation is based on the combination of standard DC characterization with the impedance spectroscopy at different bias and illumination intensity conditions. We analyzed both fresh and intentionally degraded cells. The impedance spectra show different peaks evolutions, depending on the degradation of the cells. Moreover, the same trend appears by measuring the cell at different illumination levels. To describe the cell impedance behaviors we suggest an electrical model based on distributed elements. By fitting the model to experimental data, we extrapolate the parameters related to electron transport, recombination and accumulation. The main differences between fresh and degraded samples are underlined. [ABSTRACT FROM AUTHOR]

The practical design of a wirelessly controlled portable IV-curve tracer based on a capacitive load is described. The design is optimized for the measurement of solar cell modules presenting a high open circuit voltage of up to 6 kV and a low short circuit current below 100 mA. The portable IV-tracer allows for on-site/in-situ characterization of large modules under real operating conditions and enables fast detection of potential failure of anomalies in electrical behavior. Currently available electronic loads only handle voltages up to around 1 kV. To overcome cost and safety issues related to high voltage applications, the design is based on low cost components, battery-based isolated supply and wireless communication. A prototype has been implemented and field tested for characterization of different organic photovoltaic modules (OPV) made according to the infinity concept with a large number of serially connected single junctions (~7.450 single junctions) presenting open circuit voltages up to 5.6 kV. [ABSTRACT FROM AUTHOR]

This paper presents a field-trial of organic photovoltaic (OPV) technology used within a practical application for rural electrification in Rwanda. Fourteen, large area, flexible, ITO-free, roll-to-roll processed OPV modules, encapsulated with low-cost materials, were installed on corrugated steel roofs at two sites in a rural village in Southern Rwanda and subject to continuous monitoring. This field-trial exposed modules to very high levels of insolation, in particular in the UV, high temperatures and heavy rainfall. Results show that the modules exhibit practical lifetimes (to degrade by 20% of their initial capacity) of between 2½ and 5 months, a value 5–6 times lower than control modules kept both in the dark and outdoors in Roskilde, Denmark. Degradation was primarily the result of extensive delamination caused by failure of the non-UV stable encapsulation, which led to decay in the FF, V oc and I sc of the module. [ABSTRACT FROM AUTHOR]

We report manufacture of fully printed and coated polymer solar cells on a small scale roll-to-roll coater representing the intermediate scale between laboratory and pilot scale. We highlight the enormous span in scale between the laboratory scale and the intended industrial scale by a factor of >100.000 and detail how this enormous scale must be covered by equipment that follow the scale. Especially the intermediate scale between equipment that can fit inside a fume cupboard and the typical pilot equipment with a footprint having the size of a large room presents a challenge that comprises some of the most critical steps in the scaling process. We describe the development of such a machine that comprise web guiding, tension control and surface treatment in a compact desk size that is easily moved around and also detail the development of a small cassette based flexographic unit for back electrode printing that is parsimonious in terms of ink usage and more gentle than laboratory scale flexo units where the foil transport is either driven by the flexo unit or the flexo unit is driven by the foil transport. We demonstrate fully operational flexible polymer solar cell manufacture using this new roll and roll-to-roll (R3) approach and compare with the existing methods. [ABSTRACT FROM AUTHOR]

In this study, a method to opto-electronically probe the individual junctions and carrier transport across interfaces in fully printed and coated tandem polymer solar cells is described, enabling the identification of efficiency limiting printing/coating defects. The methods used are light beam induced current (LBIC) mapping, External quantum efficiency (EQE) measurements, and monochromatic current–voltage ( I – V ) characterization. Using these methods, inherent limitations to the accuracy of EQE and LBIC measurements on non-ideal tandem solar cells are identified and described through the use of a small-signal electrical model. The model is able to predict the EQE spectrum of the non-ideal polymer tandem solar cell, using extracted values of shunt- and series resistance of the individual junction of the tandem cell. This finally enables LBIC mapping of the individual junctions of the tandem polymer solar cells, using a combination of light and voltage-biasing. [ABSTRACT FROM AUTHOR]

We present a life cycle analysis (LCA) and an environmental impact analysis (EIA) of lead based perovskite solar cells prepared according to the two most successfully reported literature methods that comprise either vapour phase deposition or solution phase deposition. We have developed the inventory for all the components employed for the two different device architectures that resemble respectively a traditional dye sensitised solar cell (DSSC) and an inverted polymer solar cell (OPV). We analyse the impacts from generation of 1 kWh of electricity and assume a lifetime of 1 year in the analysis and further present a sensitivity analysis with the operational lifetime as a basis. We find that the major impact comes from the preparation of the perovskite absorber layer due to the electrical energy required in the manufacture and also make the striking observation that the impact of toxic lead(II)halides is very limited compared to methylammoniumhalides employed. This applies during the raw materials extraction, synthesis of the starting materials and manufacture of the perovskite solar cells and from these points of view the lead based perovskite solar cells do not pose extra concerns when compared to contending solar cell technologies in the cradle-to-gate scenario considered here. The environmental impact of the perovskite solar cells in the operational phase and the decommissioning phase representing a cradle-to-grave analysis is not currently possible and will have to await large scale outdoor demonstration where emission to the environment during the operation and decommissioning phase can be measured. The main conclusion is that in the cradle-to-gate analysis there are no compelling reasons to dismiss lead based perovskites as a solar cell technology. [ABSTRACT FROM AUTHOR]

A novel cross-linkable azide-functionalized diketopyrrolopyrrole based compound DPP(BT-N3)2 was designed and synthesized via Stille coupling. Cross-linking of such molecule could help us fabricate insoluble film which could be used to fabricate heterostructures through solution processing, without dissolving the pre-patterned layers. In order to investigate the photovoltaic performances of the newly synthesized compound, large area solar cells were produced by roll coating technique. Two set of devices were fabricated by employing DPP(BT-N3)2 as either an electron donor or acceptor. A best power conversion efficiency of 0.067%, combined with an open circuit voltage of 0.53 V, and a fill factor of 37.6% were obtained for the device with DPP(BT-N3)2 as an electron acceptor. In addition, we could prove that the large area small molecule based organic solar cells could be fabricated using roll coating, which could be used in the industries for large-scale of production. [ABSTRACT FROM AUTHOR]

Abstract: Solar cells that convert sunlight into electrical power have demonstrated a large and consistent growth through several decades. The growth has spawned research on new technologies that potentially enable much faster, less costly and environmentally friendly manufacture from earth abundant materials. Here we review carbon based solar cells through a complete analysis of all the data that has been reported so far and we highlight what can be expected from carbon based technologies and draw scenarios of how it can be made of immediate use. [Copyright &y& Elsevier]

Abstract: Inverted all polymer solar cells based on a blend of a perylene diimide based polymer acceptor and a dithienosilole based polymer donor were fabricated from small area devices to roll-to-roll (R2R) coated and printed large area modules. The device performance was successfully optimized by using solvent additive to tune the phase separation. By adding 2% chloronaphthalene as solvent additive for small area (0.25cm2) devices, a power conversion efficiency (PCE) up to 0.63% was achieved for inverted geometry, higher than that (0.39%) of conventional geometry. This polymer blend showed excellent solution processibility and R2R coated and printed large area (4.2cm2) solar cells exhibited a PCE of 0.20%. [Copyright &y& Elsevier]

Abstract: New conjugated small molecules 5,5′-bis{5-Octyl-2-(2,2′-bithiophen-5-yl)-4H-thieno[2,3-c]pyrrole-4,6-dione}-3,3′-di-octylsilylene-2,2′-bithiophene DTS(BTTPD) 2 and 5,5′-bis{5-Octyl-2-(2,5-thiophenyl)-4H-thieno[2,3-c]pyrrole-4,6-dione}-3,3′-di-octylsilylene-2,2′-bithiophene DTS(TTPD) 2 of the acceptor–π–donor–π–acceptor type end-capped with thieno[2,3-c]pyrrole-4,6-dione (TPD) units for small molecule solar cells have been prepared through coupling of dithienosilole and TPD units bridged with thienylene and bithienylene. They are soluble in common organic solvents and show an interesting absorption. These small molecules have very similar optical band gaps (1.87 eV and 1.92 eV) and fairly close highest occupied molecular orbital energy levels (−5.52 to −5.55 eV). The best solar cells using DTS(TTPD) 2 as an electron donor and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as an electron acceptor demonstrated efficient performance with an obviously high open-circuit voltage (V OC) of 0.97 V and a power conversion efficiency of 1.20% after annealing and using MoO3 as electron-blocking layer. The solar cells based on DTS(BTTPD) 2 and PC61BM blend also exhibited a high V OC of 0.97 V under optimized conditions. [Copyright &y& Elsevier]

Abstract: One of the prime objects of organic solar cell research has been to improve the power conversion efficiency. Unfortunately, the accurate determination of this property is not straight forward and has led to the recommendation that record devices be tested and certified at a few accredited laboratories following rigorous ASTM and IEC standards. This work tries to address some of the issues confronting the standard laboratory in this regard. Solar simulator lamps are investigated for their light field homogeneity and direct versus diffuse components, as well as the correct device area determination using various types of masks, are discussed. The main findings are that the light field inhomogeneity and a large diffuse component in combination with masking give rise to a substantial variation in the measured efficiency. As a result the device efficiency can easily be over or underestimated. We offer a set of recommendations for the device masking and efficiency characterization that enable accurate determination of the efficiency in a standard OPV characterization laboratory. [Copyright &y& Elsevier]

Abstract: Polymer solar cell modules were prepared directly on thin flexible barrier polyethylene terephthalate foil. The performance of the modules was found to be scalable from a single cell with an area of 6cm2 to modules with a total area of up to 186cm2. The substrate thickness was also explored and the performance was found to be independent of thickness in the range of 20–130μm. The thinner substrates were found to present some challenge regarding handling but were not limited in performance. Large area modules on a substrate thickness of 45μm were finally prepared by full roll-to-roll processing employing P3HT:PCBM as the active material and were found to exhibit a total area efficiency of >1% (1000W/m−2; AM1.5G) with a typical active-area efficiency in the 1.5–1.6% for total module area of >110cm2 due to high fill factors in excess of 50%. The modules were also found to have an active-area efficiency of >1% under low light levels (∼100Wm−2). The modules were then subjected to extensive stability testing for a minimum of 1000h employing several ISOS protocols. The modules presented higher than 80% of the initial performance (T80) in the dark (ISOS-D-1), in dark under elevated temperature of 65°C (ISOS-D-2), under low light (ISOS-LL), under full sunlight (ISOS-L-2), and under outdoor testing (ISOS-O), which was conducted in two locations in India and Denmark. We estimate maximum T80 for those tests to be 2800, 5000, 1300, 1000, and 3500h respectively. The modules showed significant sensitivity to high humidity and had low values for T80 for dark storage tests at 50°C/85%RH (ISOS-D-3) and accelerated operation conditions with 0.7 sun/65 oC/50%RH (ISOS-L-3). We found the modules to be particularly suited for information and communications technology (ICT) and mobile applications where low humidity (<50%) and lower temperatures (<65°C) can be anticipated and we estimate operational lifetimes in excess of 1year. [Copyright &y& Elsevier]

Abstract: A new encapsulation method for organic solar cells has been tested on flexible solar modules and cells embedded in polyurethane, sandwiched between a tempered glass plate and a polycarbonate plate. Panels, each containing 10 organic solar modules/cells, were fabricated and installed for outdoor exposure in eight different countries for 4½ months. In order to minimize potential deviations in procedures and equipment, one person was responsible for the fabrication, installation and initial and final IV-measurements of the panels using the same equipment for all measurements and calibrations. The encapsulated modules/cells showed significantly reduced degradation compared with previous studies, with final average efficiencies around 40% of the original after 4½ months outdoor exposure. Photodegradation was furthermore found not to be the primary source of degradation. [Copyright &y& Elsevier]

Abstract: Fully roll-to-roll processed polymer solar cell modules were prepared, characterized, and laminated. Cell modules were cut from the roll and matched pairs were selected, one module with exposed cut edges, the other laminated again with the same materials and adhesive sealing fully around the cut edges. The edge sealing rim was 10mm wide. Cell modules were characterized by periodic measurements of IV curves over extended periods in a variety of conditions, as well as by a variety of spatial imaging techniques. Data show significant stability benefits of the edge sealing process. The results of the imaging experiments show that the ingress of atmospheric reactants from the edges leads to degradation. In the case of edge sealed devices the same effects are observed but significantly slowed down. In particular, the fast nonlinear degradation is eliminated. [Copyright &y& Elsevier]

Abstract: The 3-dimensional imaging of complete polymer solar cells prepared by roll-to-roll coating was carried out using high-resolution 1322nm optical coherence tomography (OCT) system. We found it possible to image the 3-dimensional structure of the entire solar cell that comprises UV-barrier, barrier material, adhesive, substrate and active solar cell multilayer structure. The achievable resolution was 12μm in the lateral plane and 4.5μm in the depth. We found that the OCT technique could be readily employed to identify coating defects in the functional layers. We finally identify the limitations of the technique, and future developments that would strengthen the use of the technique are described. [Copyright &y& Elsevier]

Abstract: Large area polymer tandem solar cells completely processed using roll-to-roll (R2R) coating and printing techniques are demonstrated. A stable tandem structure was achieved by the use of orthogonal ink solvents for the coating of all layers, including both active layers. Processing solvents included water, alcohols and chlorobenzene. Open-circuit voltages close to the expected sum of sub cell voltages were achieved, while the overall efficiency of the tandem cells was found to be limited by the low yielding back cell, which was processed from water based ink. Many of the challenges associated with upscaling the multilayer tandem cells were identified giving valuable information for future experiments and development. [Copyright &y& Elsevier]