December 1,2011, Printed Electronics USA 2011, Santa Clara, CA—Mary Boone from Plextronics described a conductive ink to enhance hole injection in printed electronics. The main target is TV, but the challenges for OLED include blue emitter lifetimes, scaling the technology to larger areas, and most importantly, scaling up manufacturing to achieve economies of scale.

Conductive polymers are moving into many applications. Flat panel displays are migrating to OLED to reduce power and costs. The conductive polymers are well suited in uses to eliminate glass substrates by replacing them with flexible substrates. These changes in materials are reflected in different profitability curves for the low-end suppliers.

OLED manufacturing is changing from vapor deposition to solution based processing in order to reduce the cost of the equipment. As the chemistries evolve, the manufacturers also can expect higher throughput and better yields than possible with the vapor systems. Although the solutions are easier to manufacture, they still have the same problems of blue and total emitter lifetimes. The full ecosystem for large-scale parts is emerging.

The whole area of hole injection layer technology, allows for lower materials energy potentials that can reduce the work function and resistive losses in a layer. Other functions within conductive layers can also help to tune optical cavities and provide a passivation layer. Some of the materials in solutions can increase the hole injection capabilities in a laminate and offset some of the degradation effects while increasing carrier lifetimes at a lower voltage.

Some of the applications for OLED are in lighting where a hybrid stack can offer advantages or at least equivalency to vapor deposition technologies. It appears that some of the other hole transport layers may also be amenable to solution processed materials rather than vapor deposited ones. Eventually, the full optical emission stack will move to solution processing.

Another ongoing area for new developments is in large area processing. One project is a 150 x 150 mm sheet to sheet printer. The challenge in R&D is to develop ink properties that map well to the film properties and also to the coding equipment requirements. The current prime candidate technology is slot die coating to provide uniform films of hole injection layers and to planarize the electrode surfaces.