This week, we spoke with Dr. Bernard Kippelen, director of the Center for Organic Photonics and Electronics (COPE) at the Georgia Institute of Technology. Dr. Kippelen was born and raised in Alsace, France. He studied at the University Louis Pasteur in Strasbourg, where he received a Maitrise in solid-state physics in 1985, and a Ph.D. in nonlinear optics in 1990. From 1990 to 1997, he was Chargé de Recherches at the CNRS, France. In 1994, he joined the faculty of the Optical Sciences Center at the University of Arizona. There, he developed a research and teaching program on polymer optics and plastic electronics.
In August 2003, Dr. Kippelen joined the School of Electrical and Computer Engineering at the Georgia Institute of Technology, where his research ranges from the investigation of fundamental physical processes (nonlinear optical activity, charge transport, light harvesting and emission), to the design, fabrication and testing of light-weight flexible optoelectronic devices and circuits based on nanostructured organic materials.
Dr. Kippelen holds 10 patents and has co-authored more than 170 refereed publications and 11 book chapters. In addition to serving as director of COPE, Dr. Kippelen is associate director of CIS:HSEM, an energy frontier research center funded by DOE. Dr. Kippelen served as chair and co-chair of numerous international conferences on organic optoelectronic materials and devices. He is the co-founder of several spin-off companies.
Printed Electronics Now: What is your background in the field of PE?
Dr. Bernard Kippelen: I was trained in solid state physics 25 years ago, and became involved in optical and physical properties of organic semiconductors in the early 1990s, when people started reporting the first high-efficiency results for organic light-emitting diodes (OLEDs), such as Dr. Ching Tang at Kodak and Dr. Richard Friend and his team at the University of Cambridge. We began work on the field of organic thin-film transistors (OTFT) 10 years ago, and were awarded a NSF grant to start a center, where we started work on organic electronics. We realized that the materials used in organic photovoltaics (OPVs), OTFTs and OLEDs were not that different, as they can all be processed at very low temperatures compared to inorganic semiconductors. In the past 10 years, we have made significant progress in improving electron field-effect mobility by two to three orders of magnitude.
COPE’s mission is academic and technology-oriented. We have an integrated multidisciplinary approach where COPE develops the science needed to fill gaps from materials to devices. As a result, we’ve had a number of recent breakthroughs. We’ve developed OTFTs with high field effect mobility values that can be processed from solution, which have shown excellent stability in air for over a year now. One of the challenges of PE is that people were very skeptical of stability of organic materials. Over time, we have shown that you can get pretty good lifetimes and can synthesize materials that are very robust.
Printed Electronics Now: How has the printed electronics industry changed since you first joined the field, and what are the key advancements that have allowed for these changes to occur?
Dr. Bernard Kippelen: The progress in the field of OTFTs has been tremendous. We set ambitious goals, and in some cases, exceeded these goals.
Meanwhile, progress continues in other areas. To get high-efficiency OPV cells is taking longer than anticipated, but the efficiencies continue to increase. I think they will reach 10% soon, which will be an important milestone, and OPV will then have a bright future. The challenge in OPV is to translate the efficiency on smaller area, single devices to modules. Right now, most modules use stripes, and you lose significant areas of the module for currents. As a result, efficiency is lagging behind a single cell.
We have continued to make progress here at COPE on OPV efficiency, having reached 6% with device geometries that didn’t use unstable metals such as calcium. If you can build devices that don’t use these reactive metals, you won’t need such stringent encapsulation, which will reduce the cost per watt.
In the early 1990s, OLEDs had an efficiency of 1%; today we have efficiencies of up to 25%. There have been a few key milestones, notably the research done by Dr. Stephen Forrest and Dr. Mark Thompson that introduced phosphorescent materials in the late 1990s.
For OTFTs, there is still room for making transistors with higher field effect mobilities.
Printed Electronics Now: What are the technical hurdles that need to be overcome to move PE forward?
Dr. Bernard Kippelen: There are multiple hurdles. As much as the progress made in PE has been tremendous, both market share today as well as the number of applications in PE is still limited. The potential of printing these products on large areas is powerful, especially if you can integrate displays, sensors and energy harvesting systems into a system. This makes the case for PE.
One of the biggest hurdles is the mismatch between the performance level reached by OTFTs and the lack of a fundamental understanding of their properties. There is a need for further study as to develop predictive modeling capabilities, especially predictive control of morphology of organic semiconductors.
We also need to improve manufacturing of these OTFTs in high yield. We need to create robust semiconductors and interfaces. This will be crucial in moving printed electronics forward.
Printed Electronics Now: Where do you see the field of printed electronics heading in both the near term and, say, 10 years from now?
Dr. Bernard Kippelen: In the near term, printed electronics will have an important impact on displays. As the use of portable devices keep growing, displays have become ubiquitous. OLED displays are the next display technology, as the stability is now good. As the technology moves forward, displays with flexible form factors will reach the market, and more printed displays and low end products will be available that will have a smaller price point and shorter lifetime.
Long term, the challenge is to secure the investments needed to move forward. For example, a lot of investors want a short term return, and OPV has a long road ahead before it can compete with other thin film and even crystalline technology on price per watt. Still, more than 50% of the cost of crystalline silicon modules is the silicon itself, and the price per watt then comes up against the ‘silicon wall.’ If you can develop OPV technology to the point where it costs 10 cents per watt, crystalline silicon will have a difficult time competing.
Sensors are another major emerging market for PE. In healthcare, being able to monitor a person’s pulse, blood pressure and blood sugar, among other measurements, can be really important. You can also use sensors to monitor infrastructure like bridges and buildings, and agriculture, where you can check on humidity and temperature. There are tremendous opportunities for low cost, robust sensors.
A lot of today’s sensors operate on batteries, and replacing them is not practical. If you can print sensors on organic thin film substrates along with organic photovoltaics, the sensors can then operate independently, which would significantly reduce the cost of ownership. There is great potential for PE.