OCiCio-PPV

OCICIO-PPV Poly[2-(3,7-dunethoxyoctyloxy)-5-methoxy-1,4-phenylene vinylene] Red-orange 610... 

Fig. 15 Fits to experimental values of the hole FET-mobility using P3F1T and OCiCio-PPV as active layers. From [100] with permission. Copyright (2007) by the American Institute of Physics...

The hole mobility /u-h in OCiCio-PPV is 5 x 10-11 m2/V s. The electron mobility /xe in PCBM is 2 x 10-7 m2/V s. However, the transport of separate charge carriers in an interpenetrating network may be different than the transport in the individual compounds. In Ref. [65] the transport and injection of charge carriers in OCiCio-PPV PCBM bulk-heterojunction diodes are investigated. 

The measured electron current in PCBM injected through Au electrode is shown in Fig. 3.35. Calculated SCL hole current in OC1C10-PPV is shown by circles in Fig. 3.35 for a thickness of L = 170 nm. Even with the high Schottky barrier of 1.4 eV (the barrier determined from the measured current is 0.76 eV) with A1 cathode for PCBM is not sufficient to suppress the electron current in PCBM below the hole current in OCiCio-PPV. With the large injection barrier the electron current is injection limited. This work shows that it is not possible to make hole only devices using OCiCio-PPV PCBM bulk heterostructures. 

Pig. VB-1 shows the temperature dependence of QEe ,(EL) of a device fabricated from a blend of OCICIO-PPV containing 20% (by weight) Bu-PBD. Lor devices with Bu-PBD, QE , increases with temperature at 85°C QE ,(EL) is twice that obtained at room temperature. The data from an identical device fabricated with pure OClClO-PPV (without Bu-PBD) are shown for comparison QEe, (EL) decreases slightly with temperature for devices made without Bu-PBD. The increase in QE t is unambiguous measurements were taken on more than 10 devices for each Bu-PBD concentration with excellent reproducibility. The increase with temperature is reversible. The increase is a function of the Bu-PBD content the optimum is at approximately 20% Bu-PBD. The increase in QEj, ,(EL) does not result from an increase in QEe (PL) QE fPL) is temperature independent (within experimental error) between room temperature and 85°C in devices fabricated with and without the Bu-PBD. 

Figure VB-1 Temperature dependence of the external quantum efficiency QEj (EL) of an LED fabricated from OClClO-PPV -i- Bu-PBD (20%) open circles data from an identical device fabricated with pure OCICIO-PPV (without Bu-PBD) are shown for comparison. Data were obtained at 6.7 mA / cm. (Taken from ref. 158)...

The PL and EL efficiencies were carefully checked on each of a series of devices fabricated with OCICIO-PPV films with different thicknesses the data are shown in Fig. VB-2. The EL and PL efficiencies track one another as the device thickness is varied. 

The first demonstration of a polymer blend transistor with appreciable ambipolar mobUities was accomplished by Meijer et al. by blending poly(2-methoxy-5-(3,7-dimethyloctoxy)- p-phenylene vinylene) (OCiCio-PPV) and PCBM (Figure 16.12a) [13]. Here, the hole and electron mobilities reached 7 x 10 cm (V s ) and 3 x 10 cm (V s ), respectively. A representation of the interpenetrating network and cross-section of the field-effect transistor is presented in Figure 16.12a. For both materials the charge injection comes from... 

In order to answer this question, Mihailetchi et al. [39] measured photogeneration in a blend of poly(2-methoxy-5-(3, 7 -dimethyloctyloxy)-phenylene vinylene (OCICIO-PPV) and PCBM as function of applied voltage and temperature. Presuming that the essential intermediate is an optically generated coulombically bound e-h pair located at an internal donor-acceptor hetero-junction that can either dissociate completely or recombine geminately, they analyzed their data in terms of Braun s model [22]. Based upon a broad distribution of e-h pair distances centered at 1.3 nm and invoking a value of 1 [is for the e-h pair lifetime they were able to rationalize their experimental results that include a measured 60% carrier yield at a built-in field of 7.5 X 10 Vcm at room temperature. However, an open question appears to be their choice of a pair lifetime of 1 [is. Recent experiments on a blend of a polyfiuo-renecopolymer and PCBM reveal a broad distribution of lifetimes albeit centered at a value as short as 1 ns [40]. 

Fig. 24 Band diagram of a blend of OCiCio-PPV and PCBM sandwiched in between two gold contacts. Due to the blending of both materials an effectively reduced transport gap is obtained leading to more balanced electron and hole injection properties. Adapted with permission from Macmillan Publishers Ltd Nature Materials [35], copyright (2003)...

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