Plexcore^® OC and OS Inks

Plexcore Semiconductors and Conducting Inks

P3HT Semiconductors
Conducting Inks

P3HT Semiconductors

Solar power and solid-state lighting hold much potential as two pathways toward practical alternative energy technology. Combined with the low-cost manufacturing methods of printed electronics, solar and solid-state lighting panels could become economical and environmentally benign solutions to current and future energy problems. Research toward making organic photovoltaic (OPV) cells and organic light emitting diodes (OLEDs) depends on availability of high-quality organic materials that will consistently perform in experimental devices. Plexcore^® organic semiconductors and conductive inks developed by Plextronics, Inc. are polythiophene-based platform technologies for organic electronic devices. They are available for your research from Aldrich Materials Science. 

Plexcore^® OS P3HT Semiconductors

Chemically, both of these p-type organic semiconductors are regioregular semi-crystalline poly(3-hexylthiophene) polymers (P3HT or RR-P3HT), which exhibit excellent spectroscopic and electronic properties (see Figure 1). The manufacturing process developed by Plextronics results in excellent batch-to-batch consistency of the Plexcore^® 2100 and Plexcore^® 1100 materials, with respect to molecular (MW), polydispersity (PDI), regioregularity, and low trace metals content. This is important for reproducible performance (e.g. conductivity) in plastic devices.

Plexcore^® OS 2100 in OPVs

Plexcore^® OS 2100, is a higher molecular weight (compared to Plexcore^® OS 1100), ultra-high purity (<25 ppm trace metals) and regioregularity (>98% head-to-tail) P3HT polymer developed for use in organic photovoltaic device applications (see Figure 2). In addition, OS 2100 can be formulated into printable inks for use in large-scale production processes, which provides material consistency and allows for reproducibility in scale-up device research.

Figure 1: Chemical Structure of Plexcore® OS 2100 (698997) & OS 1100 (698989).		Figure 2: OPV cells printed using Plexcore® OS 2100 semiconductor.

Figure 3a shows a schematic of an OPV device stack. The photoactive layer consists of a Plexcore^® OS 2100 mixture with [6,6] phenyl C₆₁ butyric acid methyl ester (PCBM, e.g. 684449), which is formulated into a photoactive ink and spin-coated onto the hole transport layer (HTL) to fabricate an OPV device. The P3HT-PCBM bulk heterojunction within the OPV device active layer ensures good charge separation (exciton dissociation) and efficient charge transport to electrodes of the OPV cell.

The I-V curve below (Figure 3b) shows performance of a typical P3HT-PCBM OPV cell employing Plexcore^® 2100 material and certified by the National Renewable Energy Laboratory (NREL) at 3.39% efficiency. This is typical performance of a P3HT: PCBM cell; higher performance levels can be achieved by careful optimisation of this OPV system For example, power conversion efficiency of about 4.4% has already been demonstrated for a P3HT:PCBM blend.¹

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Figure 3a: P3HT-PCBM OPV Device Stack; ITO: Indium Tin Oxide; PCBM: [6,6] phenyl C61 butyricacid methyl ester (684449); Ca/Al: Calcium/Aluminum		Figure 3b: I-V curve for a typical Plexcore 2100 OPV cell.

For additional information relating to processing of Plexcore^® OS 2100 for device fabrication, see Tech Bulletin AL-250.

Follow this link for additional information about PCBM semiconductors.

Plexcore^® OS 1100 in OFETs

Plexcore^® OS 1100 is a lower molecular weight (relative to Plexcore^® OS 2100) P3HT polymer semiconductor optimized for application in the active layers of Organic Field Effect Transistors (OFETs). P3HT OFETs are typically made in bottom-gate configuration (Figure 4a), but the material can also deliver a higher hole current in other device architectures: charge carrier mobility in the range of 5×10^-4 cm²/Vs and an ON/OFF ratio of 10⁴ are typical in bottom gate OFETs with channel length:width ratio of 10:10,000 microns. Specific device performance depends on P3HT film morphology that, in turn, is affected by coating parameters and polymer properties, including regioregularity. Figure 4b depicts typical performance of a bottom-gate OFET.

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Figure 4a: Plexcore® OS 1100 in Bottom-Gate Organic Field Effect Transistor (OFET): hexamethyldisilazane (40215); Au/Ti: Gold/Titanium.		Figure 4b: Performance of a Plexcore® OS 1100 Bottom-Gate Organic Field Effect Transistor (OFET).

For information relating to processing of Plexcore^® OS 1100 for device fabrication, see Tech Bulletin AL-248.

Table 1: Plexcore^® OS 2100 and Plexcore^® OS 1100.

Plexcore^® OC Conducting Inks

Employing the regioselective polymerization techniques used to make P3HTs, Plextronics has developed a self-doping polymer poly(thiophene-3-[2[(2-methoxyethoxy)ethoxy]-2,5-diyl) (Figure 5), which is available as ready-to-use solutions for making hole injection layers (HIL) in OLED (organic light-emitting diode) devices (in combination with a matrix polymer and other additives, see Figure 6).

Plexcore^® OC 1100 or 1200 can be spin-coated onto an ITO-coated glass substrate to fabricate an HIL of a hybrid phosphorescent organic light emitting diode (PHOLED) device (Figure 7). Advantages of Plexcore^® OC materials include reduced acidity (for decreased electrode degradation), tunable properties for specific device optimization and versatility, and easy solution processing. Furthermore, the unique versatility of Plexcore^® OC can be utilized to match the work function of the hole injection layer to the rest of the device stack. This minimizes injection losses at interfaces, enables low voltage device operation, and extension of device lifetime. Plexcore^® OC materials are compatible with a wide variety of device architectures, including vapor deposited OLEDs and polymer OLEDs with poly(phenylene vinyline) (PPV) and polyfluorene emitters. 

Figure 7: OLED device stack; ITO: Indium Tin Oxide;
NPB: N,N’-Bis(naphthalen-1-yl)-N,N’-bis(phenyl)benzidine (556696)
CBP: 4,4’-N,N’-dicarbazole-biphenyl (699195);
Ir(ppy)₃: tris-[2-phenylpyridinato-C2,N]iridium(III) (694924);
BCP: 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine) (699152);
Alq₃: tris-8-hydroxyquinoline aluminium (697737); Ca/Al: Calcium/Aluminium

Figure 8 shows representative performance of green PHOLEDs made with Plexcore^® OC 1200 (Figure 8a) and Plexcore^® OC 1100 (Figure 8b). Turn on voltage of the devices is at the band gap of the emitter, indicating low interfacial energy barriers, which can be attributed to efficient hole injection. This leads to efficiencies up to 14-15 cd/A, with modest efficiency drop-off at increasing current density.

Figure 8a: Plexcore^® OC 1200 (699780) (Performance in PHOLED)

Figure 8b: Plexcore^® OC 1100 (699799) (Performance in PHOLED)

Power efficiency of a PHOLED device utilizing Plexcore^® OC as the HIL is shown in Figure 9. The loss in power efficacy is minimized up to 1,000 units of brightness using the Plexcore^® OC technology.

Figure 9: Power Efficiency of a PHOLED Device with Plexcore^® OC HIL.

For information relating to processing of conducting inks for device fabrication, see Technical Bulletin AL-251.

Table 2: Plexcore^® OC 1100 and Plexcore^® OC 1200

Reference:

1. Li, G.; Shotriya, V.; Huang, J.; Tao, Y.; Moriarty, T.; Emery, K.; Yang, Y.; High-Efficiency Solution Processable Polymer Photovoltaic Cells by Self-Organization of Polymer Blends, Nat. Mater. 4, (2005), 864-868.

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