• Energy Research

Procedures for testing organic solar cell devices and modules with respect to stability and operational lifetime are described. The descriptions represent a consensus of the discussion and conclusions reached during the first 3 years of the international summit on OPV stability (ISOS). The procedures include directions for shelf life testing, outdoor testing, laboratory weathering testing and thermal cycling testing, as well as guidelines for reporting data. These procedures are not meant to be qualification tests, but rather generally agreed test conditions and practices to allow ready comparison between laboratories and to help improving the reliability of reported values. Failure mechanisms and detailed degradation mechanisms are not covered in this report. © 2011 Elsevier B.V. All rights reserved.

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In the present study, quantum chemical methods were applied to investigate the energy levels of the frontier orbital of mono and multi adducts of diphenylmethanofullerenes (DPMs). Recently these molecules have been used as electron acceptors in polymer solar cells showing interesting properties compared to the widely used [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM). The geometries of all the investigated compounds were optimized with the density functional theory at the B3LYP/3-21G level of calculation. We studied the effect of electron-donating (methoxy and methyl thioether) and electron-withdrawing (fluorine) substituents (placed on the diphenylmethano addend in ortho, meta and para position of the phenyl rings), on the lowest unoccupied molecular orbital (LUMO) level of DPM. Afterward, we analysed all the possible isomers arising from bis and tris additions to fullerene cage. The LUMO level is significantly raised compared to the mono adduct but different isomers have different LUMO levels. Since the open circuit voltage (V(oc)) for polymer solar cells with ohmic contacts is proportional to the difference between the highest occupied molecular orbital (HOMO) of the donor polymer and the LUMO of the acceptor (fullerene), these bisadducts have the potential to increase the V(oc) of the corresponding devices.

Accurate characterization and reporting of organic photovoltaic (OPV) device performance reniains one of the important challenges in the field. The large spread among the efficiencies of devices with the same structure reported by different groups is significantly caused by different procedures and equipment used during testing. The presented article addresses this issue by offering a new method of device testing using "suitcase sample" approach combined with outdoor testing that limits the diversity of the equipment, and a strict measurement protocol. A round robin outdoor characterization of roll-to-roll coated OPV cells and modules conducted among 46 laboratories worldwide is presented, where the samples and the testing equipment were integrated in a compact suitcase that served both as a sample transportation tool and as a holder and test equipment during testing. In addition, an internet based coordination was used via plasticphotovoltaics.org that allowed fast and efficient communication among participants and provided a controlled reporting format for the results that eased the analysis of the data. The reported deviations among the laboratories were limited to 5% when compared to the Si reference device integrated in the suitcase and were up to 8% when calculated using the local irradiance data. Therefore, this method offers a fast, cheap and efficient tool for sample sharing and testing that allows conducting outdoor measurements of OPV devices in a reproducible manner. (C) 2014 Elsevier B.V. All rights reserved.

Abstract In the present study, semiempirical and density functional molecular orbital calculations are performed on fullerene derivatives with varying reduction potentials, successfully used as an electron acceptor in bulk heterojunction solar cells. The geometries of all the compounds were optimized with the semiempirical PM3 method. Density functional theory (DFT) single-point calculations, B3LYP/3-21G*, have been carried out with the aim to investigate the energy levels of the frontier orbitals. We have correlated the theoretical lowest unoccupied molecular orbital (LUMO) levels of different fullerenes with the open-circuit voltage of the photovoltaic device based on the blend of poly[2-methoxy-5-(3,7-dimethyloctyloxy)]–1,4-phenylenevinylene (MDMO–PPV) with the acceptor molecules. We have also investigated the influence of new substituents on the LUMO level of the parent fullerene showing the possibility to further increase the open-circuit voltage of the MDMO–PPV:fullerene device.

Here we report, the synthesis, the spectroscopic and photovoltaic characterization of two alternating copolymers based on (octylsulfanyl)bithiophene and differently substituted benzodithiophene units (BDT). Bulk heterojunction (BHJ) polymer solar cells (PSCs) having as active layer a blend of these polymers as donor materials and [70]PCBM as acceptor material were prepared and investigated. The geometry of the device is: glass/ITO/PEDOT:PSS/blend/Ca/Al. The electrical performances of the cells were compared in order to study both the influence of the insertion of a benzodithiophene unit in the (alkylsulfanyl)bithiophene backbone and the effect of different substituents on benzodithiophene unit. The best realized device shows a power conversion efficiency of 2.3% under 100 mW/cm2 AM 1.5G illumination.

Abstract We present the synthesis and characterization of a novel copolymer from benzodithiophene and alkylsulfanyl-bithiophene units, poly[4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b′]dithiophene-alt-4,4′-bis(octylsulfanyl)-2,2′-bithiophene] (PolyS). The structural, electrochemical and photophysical properties of PolyS were investigated by gel permeation chromatography (GPC), thermogravimetric analysis (TGA), NMR, UV–vis, photoluminescence (PL) spectroscopy and cyclic voltammetry (CV). PolyS was used to fabricate bulk-heterojunction polymer solar cells (PSCs) in combination with the [60]PCBM and [70]PCBM (electron acceptors). The device realized using [70]PCBM shows a better current output due to the increased absorption of the blend film compared to the PolyS:[60]PCBM one. The power conversion efficiency of the best PSC realized is 2.3% under 100 mW/cm2 AM 1.5 G illumination.