I did my doctoral work with Dr. Salaneck, and now we share the same laboratory facilities, so in that sense we work together a lot. We still have a strong collaboration.

I would say the understanding is still evolving. When I started in the field, we had very little understanding of what was happening in these materials. Now I think we have a fairly clear idea, although there some i’s and t’s left to be dotted and crossed. What has brought the field forward actually is improved chemistry and the fact that the materials available since the late 1990s and certainly now are much better than the materials available to work with a decade earlier—specifically the consistency of the materials. When I started in this field, from one batch to another the materials would be quite different. Now, they’re more or less the same every time, and that’s led to the beginning of commercialization.

In some sense the true heroes in this business are the chemists. That’s where the most impressive development has been. And because of that we can now really attack the physics questions. The materials are what they’re supposed to be and our experiments are more consistent. We don’t have to worry about spurious results because of something unexpected happening with the materials.

And to an extent, if you look at the transistor business, that is also what is now driving it—better and better materials, with higher mobilities and better stability in terms of ambiance and contamination. Some older materials would be oxidized and p-doped just by contact with the atmosphere. That kind of problem is now well on the way to being solved.

One of the remaining questions is about the interface-forming properties of these materials. That’s what we’ve been working on. There are a lot of different views about what is actually occurring at the interfaces between polymers and organic contacts or even between polymers and metal contacts. Understanding how strong the materials are coupled, how that determines structural changes at the atomic level, and what types of barriers you get to those interfaces are critical questions. So one area of high scientific interest is in understanding how to model that in a device, what type of interface you get. There again, having really nice materials helps.

If the coupling is really strong it can modify the organic material, breaking bonds and forming new ones. Then you completely change the electron structure at the interface; you may introduce new energy levels, trapped states, etc. If you form real chemical bonds, then there has to be charge transfer, which would shift energy levels up or down, and which would again change the barriers toward injection.

Then you have medium-strength interactions. They don’t have real chemical bonds, but there’s still some interaction between the molecular orbitals of the organic material and the continuum of states of metal on a Fermi level. That causes a broadening of the highest occupied molecular orbital and the lowest-occupied molecular orbital, which in turn often introduces charge transfer across the interface, building up a dipole.

Then there are the weak interactions. Say, if you ink print or spin coat a polymer on the surface, you can still have charge transfer across that interface—tunneling—depending on how the energy levels are aligned compared to the Fermi level of the metal and the charge-carrying species in the polymer. Again, that gives you a different type of barrier than in the other two cases. How to properly define these three scenarios and, more importantly, to know when one of these three occurs, that’s the subject of a very healthy ongoing debate.

For the commercialization of the technology, it’s still in the materials. There has been a lot of progress, but long-term stability is still an issue. It may be on its way to being solved, but at the moment it’s still a problem.

As for the science itself, I think the biggest challenge, which we may be over, has been agreeing upon how to describe the static energy level alignment of interfaces; how to make a proper description of that and then to go forward and actually study the dynamics of charge injections—what happens when we actually start injecting charges. That is much harder to study experimentally.

From my perspective, as a spectroscopy and materials guy, that’s the next thing in my research. A device guy will tell you something different. But from my perspective, the first thing we have to clean up is this issue of the statics of the interface-forming properties.

I’ve never actually contemplated such a possibility since that’s very far removed from my present situation. Realistically what I would like to do, and this may actually happen in the next couple of years, is dynamic studies using laser pulses in combination with synchrotron radiation to do what’s basically a pump-probe experiment to study these interfaces. That would be one way to improve our understanding without venturing too far into the realm of science fiction. It wouldn’t cost too much and it’s doable with the knowledge we have now.

The commercialization of these devices will continue to improve, but I would actually expect the scientific interest to diminish a little, because the better you can actually make something, the fewer questions are left to be answered. So if things continue to improve on the commercial side, the odds of learning anything substantially new about these materials and devices will get lower. I think as one goes up, the other naturally goes down. But then interest may move in other directions. Things like organic spintronics and organic bioelectronics may become the next big thing, and we’re already seeing some of that shift in direction.

Spintronics is regular electronics, but you also use the fact that the electron has a spin and that in turn can generate a signal—a zero or one in some sense. The electron rotates around its own axis, which means it has an intrinsic spin, and that spin can be measured. It’s an extra degree of freedom. You can make it so that electrons spinning in one direction, for instance, will go through a wire, but not those spinning in the other direction. This kind of manipulation is the essence of spintronics, and you can then make these devices either completely organic or hybrids.

Organic bioelectronics refers to devices that interact with the human body as sensors or other things. There’s quite a lot of interest now from companies in organic bioelectronics and that’s looking like it could be the next big thing.