This work is part of the inter-laboratory collaboration to study the stability of seven distinct sets of state-of-the-art organic photovoltaic (OPVs) devices prepared by leading research laboratories. All devices have been shipped to and degraded at the Danish Technical University (DTU, formerly RISO-DTU) up to 1830 hours in accordance with established ISOS-3 protocols under defined illumination conditions. In this work we present a summary of the degradation response observed for the NREL sample, an inverted OPV of the type ITO/ZnO/P3HT:PCBM/PEDOT:PSS/Ag/Al, under full sun stability test. The results reported from the combination of the different characterization techniques results in a proposed degradation mechanism. The final conclusion is that the failure of the photovoltaic response of the device is mainly due to the degradation of the electrodes and not to the active materials of the solar cell.
Seven distinct sets (n ≥ 12) of state of the art organic photovoltaic devices were prepared by leading research laboratories in a collaboration
planned at the Third International Summit on Organic Photovoltaic Stability (ISOS-3). All devices were shipped to DTU and characterized
simultaneously up to 1830 h in accordance with established ISOS-3 protocols under three distinct illumination conditions: accelerated full sun
simulation; low level indoor fluorescent lighting; and dark storage with daily measurement under full sun simulation. Three nominally
identical devices were used in each experiment both to provide an assessment of the homogeneity of the samples and to distribute samples for
a variety of post soaking analytical measurements at six distinct laboratories enabling comparison at various stages in the degradation of the
devices. Characterization includes current-voltage curves, light beam induced current (LBIC) imaging, dark lock-in thermography (DLIT),
photoluminescence (PL), electroluminescence (EL), in situ incident photon-to-electron conversion efficiency (IPCE), time of flight secondary
ion mass spectrometry (TOF-SIMS), cross sectional electron microscopy (SEM), UV visible spectroscopy, fluorescence microscopy, and
atomic force microscopy (AFM). Over 100 devices with more than 300 cells were used in the study. We present here design of the device
sets, results both on individual devices and uniformity of device sets from the wide range of characterization methods applied at different
stages of aging under the three illumination conditions. We will discuss how these data can help elucidate the degradation mechanisms as well
as the benefits and challenges associated with the unprecedented size of the collaboration.
The synthesis of copolymers based on thiophene, benzothiadiazole and benzo-bis-thiadiazole are described. The
polymers were obtained by employing Stille cross coupling polymerization. The polymers were characterized by NMR,
size exclusion chromatography, UV-vis and ultraviolet photoelectron spectroscopy. The results obtained from UV-vis
and ultraviolet photoelectron spectroscopy showed band gaps of 2.1-1.7 eV for polymers based on benzothiadiazole and
0.7 eV for polymers based on benzo-bis-thiadiazole. Furthermore the results showed that the band gap decreases with an
increase in the number, n, of thiophenes in the polymer repeating unit (n= 1-4). Large area photovoltaic devices were
prepared and the results of these devices are described.
The synthesis of conjugated low band-gap copolymers based on thiophene and benzothiadiazole is described. The synthesis was carried out by oxidative ferric chloride polymerization or Stille cross coupling polymerization. The solubility of the polymer based on quarterthiophene and benzothiadiazole was tested with hexyl, 2-ethyl-hexyl and dodecyl as side chains on the thiophene. It was found that 2-ethyl-hexyl substituents gave high molecular weight polymer products with good film forming ability and good solubility. The polymers based on di-thiophene and benzothiadiazole were applied in photovoltaic devices and the coupling of the alkylthiophene showed no effect on the maximum photovoltaic performance. Band-gaps were estimated to be 2 eV for polymers based on di-thiophene and benzothiadiazole and 1.8 eV for polymers based on quarterthiophene and benzothiadiazole. Attempts to synthesize the polymers with a benzo-bis-thiadiazole unit are also described.
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