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 work focuses on the degradation of performance induced by both water and oxygen in an inverted geometry organic photovoltaic device with emphasis on the accumulated barrier effect of the layers comprising the layer stack. By studying the exchange of oxygen in the zinc oxide (ZnO) layer, the barrier effect is reported in both a dry oxygen atmosphere and an oxygen-free humid atmosphere. The devices under study are comprised of a bulk heterojunction formed by poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester sandwiched between a layer of zinc oxide (electron transporting layer) and a layer of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (hole transport layer) and the two electrodes indium tin oxide and silver. Time-of-flight secondary ion mass spectrometry is employed to characterize the accumulated barrier effect. A pronounced barrier effect is observed in the humid atmosphere, correlating well with a long observed lifetime in the same atmosphere
Polymer solar cells have many advantages such as light weight, flexibility, environmental friendliness, low thermal
budget, low cost and most notably very fast modes of production by printing techniques. Production experiments have
shown that it is highly feasible with existing technology to mass produce polymer solar cells at a very low cost. We have
employed state-of-the-art analytical techniques to address the challenging issues of degradation and stability of R2R
manufactured devices. We have specifically studied the relative effect of oxygen and water on the operational devices in
regard to degradation.
Insufficient lifetimes of organic photovoltaics are manifested in a reduced photovoltaic response, which is a consequence of physical and chemical degradation of the photovoltaic device. To prevent degradation it is vital to gain detailed insight into the degradation mechanisms. This is possible by utilizing state-of-the-art characterization techniques such as TOF-SIMS, XPS, AFM, SEM, interference microscopy and fluorescence microscopy as well as isotopic labeling (18O2 and H218O). By a combination of lateral and vertical analyses of the devices we obtain in-depth and in-plane information on the reactions and changes that take place in the various layers and interfaces. Examples will be presented that describe the advantages and disadvantages of various characterization techniques in relation to obtaining information on the degradation behavior of complete photovoltaic devices.
The degradation mechanisms of conjugated polymer materials used in organic photovoltaic cells were studied. To elucidate the parts of the degradation mechanisms induced by molecular oxygen, isotopic labeling was employed in conjunction with time-of-flight secondary ion mass spectrometry (TOF-SIMS). Devices that were kept in the dark were compared with devices that had been subjected to illumination under simulated sunlight. It was found that molecular oxygen diffuses into the device causing oxygen-containing species to be generated throughout the active layers. The isotopic labeling combined with TOF-SIMS depth profiling and imaging allowed mapping of the oxidation processes by measuring the vertical and lateral distribution of oxygen-containing species. The exact pinpointing of the parts of the device that are susceptible to oxidation allows for a mechanism to be proposed that partly explains the device failure manifested in the insufficient life times of the organic photovoltaics.
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