Organic photovoltaics are the focus of intense research efforts due to the low-cost of processing and their
potential applications in flexible electronics. We herein report efficient, thick (2,500 Å) photovoltaic devices based on
ternary mixtures of polycarbonate linked TPD (N,N,N',N'-tetrakis(phenyl) benzidine)) polymer (PTPD), small
molecular weight radical salt of a TPD derivative and C60 in an ITO/blend/Al configurations. While the addition of
electron acceptor C60 moiety to PTPD produces a 3 orders more, short circuit current (Isc) of 0.22 mA/cm2, the presence of salt increased it further to 0.33 mA/cm2. This is attributed to the increased hole conductivity and absorption of PTPD matrix due to the presence of salt. In these 'PTPD/salt/C60' ternary blend devices, the fill factors as well as the power conversion efficiencies increased with increasing salt concentration with the highest fill factor of 0.4 and power conversion efficiency of 0.47% obtained in 10% salt doped ternary ITO/PTPD-salt-C60/Al device. To the best of our
knowledge this is the first time that a radical salt has been used into an organic photovoltaic device configuration. Along
with discussing these results, we would also be discussing the interplay of the three components of this ternary system to
both open circuit voltage (Voc) and Isc. Further optimization in structure and morphology of these devices can lead to significant performance enhancement.
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.
In this study molecular doping in non-conjugated polymeric systems is utilized in order to obtain high efficiency electrophosphorescent light emitting devices (PHOLEDs). The device consists of a light emitting thin film layer composed of hole and electron transporting moieties dispersed in a polymer matrix of polyvinylcarbazole (PVK). Light emission is obtained by harvesting singlet as well as triplet excitons by means of a phosphorescent dye, Iridium (III) tris(2-(4-tolyl)pyridinato-N,C2) (Ir(m-ppy)3), also dispersed in the polymer matrix. By incorporating a low conductivity polyethylene dioxythiophene-polystyrene-sulfonate (PEDOT) hole injection layer between the indium tin oxide transparent anode and the light emitting molecularly doped layer, the efficiency of these devices reaches values as high as 41 cd/A with a peak luminous efficacy of 28 lm/W. At the same time, triplet quenching by the hole transporting moiety as well as the electrodes are expected to be limiting the efficiency of these devices. In this paper we discuss several alternative device architectures studied in order to understand the factors affecting the device performance. In particular the effect of incorporating alternative hole transporting moieties and hole blocking layers are addressed.
Conduction in aluminum(III) 8-hydroxyquinoline (Alq3)- based organic light-emitting diodes (OLEDs) was modeled based on trapped charge-limited conduction of electrons in the Alq3 bulk. This model was chosen since it can easily incorporate an arbitrary trap distribution such as may arise during the material's degradation. The evolution of a narrow Gaussian distribution of localized trap states below the lowest unoccupied molecular orbital (LUMO) of Alq3, lying against a natural exponential background, was used to explain changes in the current-voltage characteristic and external quantum efficiency with time observed by many researchers for organic light-emitting diodes. Based on the change of the shape of the DC current density vs. voltage (J-V) curve, the depth of the electron trap states that were formed during aging was about 0.25 eV below the LUMO of Alq3. This value is consistent with electrochemical measurements of known chemical degradation products. The J-V characteristics show behavior which is suggestive of a trap- filled limit, and this is discussed along with the general appropriateness of the model used.
Conference Committee Involvement (5)
Organic Light Emitting Materials and Devices XX
28 August 2016 | San Diego, California, United States
Organic Light Emitting Materials and Devices XIX
9 August 2015 | San Diego, California, United States
Organic Light Emitting Materials and Devices XVIII
17 August 2014 | San Diego, California, United States
Organic Light Emitting Materials and Devices XVII
25 August 2013 | San Diego, California, United States
Organic Light Emitting Materials and Devices XVI
12 August 2012 | San Diego, California, United States
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