Large area organic photovoltaic modules have been fabricated with 232.8 cm2 of total area with 108 cm2
of photoactive area. Efficiencies up to 2.3% by active area (1.1% by total area) demonstrate operation of a multicell module with configurable voltage and current output. NREL certification
is reported and is an example of the largest OPV module certified by NREL, as well as the only polymer:fullerene-based module tested. Module lifetime data were collected and with ca. 550 h of
light-soaking, > 2000h of lifetime is expected based on extrapolation. The conditions of the test were 100% duty cycle, ~ 1 Sun Xe-arc lamp, KG5-Si reference, ~25 °C controlled
temperature. The lifetime data were normalized with respect to the variations and fade of the Xe-arc lamp source.
We report NREL-certified efficiencies and initial lifetime data for organic photovoltaic (OPV) cells based on Plexcore
PV photoactive layer and Plexcore HTL-OPV hole transport layer technology. Plexcore PV-F3, a photoactive layer
OPV ink, was certified in a single-layer OPV cell at the National Renewable Energy Laboratory (NREL) at 5.4%, which
represents the highest official mark for a single-layer organic solar cell. We have fabricated and measured P3HT:PCBM
solar cells with a peak efficiency of 4.4% and typical efficiencies of 3 - 4% (internal, NREL-calibrated measurement)
with P3HT manufactured at Plextronics by the Grignard Metathesis (GRIM) method. Outdoor and accelerated lifetime
testing of these devices is reported. Both Plexcore PV-F3 and P3HT:PCBM-based OPV cells exhibit >750 hours of
outdoor roof-top, non-accelerated lifetime with less than 8% loss in initial efficiency for both active layer systems when
exposed continuously to the climate of Western Pennsylvania. These devices are continuously being tested to date.
Accelerated testing using a high-intensity (1000W) metal-halide lamp affords shorter lifetimes; however, the true
acceleration factor is still to be determined.
We report the observation of cathodoluminescence (CL) of organic multilayers of tris-(8-hydroxyquinoline) aluminium (Alq3) and 2- (4biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD) deposited on ITO-coated glass, with and without hole transport layer and compare it with electroluminescence (EL) from similar devices. Excitation of the CL of such multilayer organic anodes was accomplished by low energy electrons field emitted by single walled carbon nanotube
cathodes. The dependence of CL spectrum and intensity on voltage (V), current (I), type of transport layer and the cathode-anode geometry has been studied. We propose carbon nanotubes as efficient cathodes for stable CL emission from multi-layer anodes at small cathode-anode separations. The role of hole-transport layer is also discussed.
We report a novel type of nanocomposite of conjugated polymer (regio-regular polythiophene) with infrared-sensitive, PbSe quantum dots (QD), which have size-tunable lowest-energy absorption bands between 0.3 and 1 eV. Thin film devices show very good diode characteristics and sizable photovoltaic response with an open circuit voltage, Voc, of ~ 0.3-0.4 V and short circuit current density, Jsc, of ~ 0.2mA/cm2, which is significantly higher than recently reported in PbS QD-based devices. This is the evidence of a quite efficient photoinduced charge transfer between the polymer and QD, with infrared sensitivity. Photocurrent under reverse bias is significantly enhanced to Jph ~ 1 mA/cm2 indicating that the polythiophene/PbSe QD system can be used as effective infrared photodetectors. Detailed spectroscopic studies of photoresponse over a wide spectral range are presented. Quenching of photoluminescence by PbSe QDs has also been studied to gain more understanding of energy and charge transfer in this system.
We present this detailed study of a postproduction heat treatment of flexible organic solar cells based on regio-regular (RR) P3HT:PCBM composite in a wide temperature range from 75°C to 150°C. The efficiency of the photovoltaic device was significantly improved by postproduction heat treatment and both optimal annealing temperature and time dependencies were determined. Optimized parameters yielded >3% efficiency for devices on glass substrates and, using these optimized parameters, an efficiency of >2% was found for devices fabricated on flexible substrates. The optimal phase separation of PCBM and RR-P3HT into bi-continuous network structure occurs within a very short period of time and are very stable. We found that optimal concentration of PCBM in a RR-P3HT matrix is rather low, only 34 w.%. We show the performance of plastic solar cells fabricated on flexible substrates (ITO coated PET) using these optimized heat treatment parameters.
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