The Future of Photovoltaics Is Organic: A Conversation with KAUST’s Dr. Thomas Anthopoulos

The race for more efficient photovoltaic (PV) technologies is a constant area of research around the globe. 

But did you know that many next-gen PVs use organic technologies?

AAC sat down (virtually) with one of the researchers blazing trails in OPVs (organic photovoltaics), Dr. Thomas Anthopoulos. Dr. Anthopoulos and his colleagues at KAUST (King Abdullah University of Science and Technology) in Saudi Arabia develop new methods of developing OPVs to out-perform traditional inorganic photovoltaics.

 

Dr. Thomas Anthopoulos

 

Dr. Anthopoulos's background is, as he puts it, "a little bit unconventional." His career began in medical engineering but he quickly determined that it wasn't where his heart lay. He shifted gears to pursue a Ph.D. in Physical Electronics with a focus on molecular semiconductors. After completing his Ph.D., he found a slew of opportunities awaiting him in the intersection of electronics and organic material science.

Postdoc, he first studied OLEDs (organic light-emitting diodes) for two years at the University of St. Andrews in Scotland, and then moved on to study printed organic microelectronics at the Philips Research Labs in the Netherlands.

In 2005, Dr. Anthopoulos was awarded an Engineering and Physical Research Council (EPSRC) Advanced Fellowship hosted by the Imperial College London's (ICL) Physics Department, which "essentially paved the way to my academic career." Over the next seven years, he joined ICL to establish his first research group and progress through the academic ranks before becoming a full professor of experimental physics.

In 2017, he and his family moved to Saudi Arabia to join King Abdullah University of Science and Technology (KAUST). There, he's a member of the Material Science and Engineering Program and KAUST Solar Centre (KSC) and works on OPV research. In the last year alone, his group has had major achievements that could be formative to the future of OPV technology.

 

Work at KAUST

AAC: First, could you discuss some of the research projects that you're currently involved in at KAUST? 

TA: Efforts at KAUST Solar Centre (KSC) in the field of OPVs are very diverse and include the development of new materials as well as innovative device concepts. This includes organic, inorganic, and hybrid materials such as metal halide perovskites.

In the OPV field, emphasis is placed on improving the efficiency of OPVs and their stability either via new materials development or innovative additive strategies. The development of tandem OPVs is also a priority for us, not only for improving the power generation of the OPV cells but also for the generation of green hydrogen. This effort is complemented by work in my group on the design and development of new forms of water splitting reactors.

 

AAC: On a more general note, which emerging or existing renewable energy technologies on the market do you feel are the most promising and why? 

TA: If we exclude established technologies such as wind and hydropower, then I believe photovoltaics is definitely amongst the most promising techs. PV technologies continue to evolve in different forms and shapes, finding applications from massive solar farms to building integrated systems all the way to tiny power sources for the IoT device/system ecosystem.

Importantly, PV tech appears a highly attractive option for the production of green hydrogen, which many argue is the next big thing in energy. My group is very interested in this field with a focus on the development of better solar cells, as well as the development of new electrolyzer technologies. 

 

The Promise of Organic Photovoltaics (OPVs)

AAC: What research topics are your team at the KAUST Solar Centre currently focusing on?

TA: Broadly speaking, our work focuses on emerging material technologies and innovative processing methodologies for future optoelectronics. We are particularly interested in photovoltaics (PVs), solid-state lighting, telecommunications, sensing, energy storage, and the combination and application of these technologies in the internet of things device ecosystem.

Among those topics, research on third-generation PV technologies (technologies that can be manufactured via upscalable techniques, such as printing) is one of the most promising areas due to its potential for near-term impact, with organic PVs (OPVs) being closest to my heart.

 

Dr. Anthopoulos (left) in 2019 with his KAUST colleagues (left to right) Yuanbao Lin, Yuliar Firdaus, and Begimai Adilbekova with their tungsten disulfide solution for OPVs. Image used courtesy of KAUST

 

AAC: What are some of the current challenges in the development of OPVs and other solar technologies that you have been working on?

TA: Power conversion efficiency, stability, and cost are the three primary challenges OPVs face today. The cost of materials, especially state-of-the-art systems, remains high, but I think this will eventually be addressed once the economies of scale kick in.

In the past five years, tremendous strides have been made in all three areas and we have every reason to believe that progress will continue for years to come. As an academic, I am personally very interested to see how far we could push the efficiency of OPVs and I worry less about the industrial aspects of the technology. 

 

AAC: How do you think challenges for OPVs could be overcome in the future?

TA: The OPV community is already making significant strides in addressing all these challenges. Recent years have witnessed progress in two key areas:

i) the development of new materials, and

ii) establishing an improved understanding of the key physical processes that govern device operation and, ultimately, performance.

We are now at a point where the power conversion efficiency of the best OPVs is nearing 20% and we have every reason to believe that this could potentially reach 25% or more. The most exciting aspect of the OPV work is that there is literally an infinite number of potential materials—what I call a materials zoo—offering endless possibilities. The challenge there is not to get lost.

Moreover, the tremendous potential for upscalable manufacturing combined with the form-free aspects of the OPV technology, makes it the ideal technology platform for future applications. 

 

The most exciting aspect of the OPV work is that there is literally an infinite number of potential materials—what I call a materials zoo—offering endless possibilities. The challenge there is not to get lost.

 

AAC: Could you share some of your recent achievements in terms of the development of organic photovoltaic cells (OPVs)? 

TA: I will highlight two recent achievements from my group that I believe could have important implications to future developments in the area of OPVs. 

The first relates to the use of molecular dopants to improve both the power conversion efficiency and stability of OPVs (see Advanced Science 2020, 7, 1903419; ACS Energy Letters 2020, 5, 3663). Our findings went against conventional wisdom and contrasted previous findings which had concluded that molecular doping shouldn’t work. Our work showed that intrinsic deficiencies often associated with organic semiconductors can be addressed through the addition of carefully engineered molecular dopant. We discovered that careful selection of dopants incorporated within the active region of the device at the right amounts could yield significant and consistent improvements. Importantly the approach appears to be applicable to a range of state-of-the-art OPV materials. 

The second accomplishment is the development of various interlayer materials. Such interlayers are integral parts of many organic optoelectronics including OLEDs, OPVs, and organic photodetectors. A recent example that highlights the potential of our work is the development of self-assembled monolayers (SAMs) as hole-extraction interlayers for state-of-the-art OPVs (see ACS Energy Letters 2020, 5 (9), 2935).

Our technology combines bottom-up self-assembly with carefully designed molecules, which in turn enables simplified processing with extreme precision down to the molecular level. We are now in the process of developing improved SAM technologies, as well as exploring their use in a range of other applications.

 

AAC: What role do you think OPVs will play in the future and how could these technologies help us to tackle current environmental challenges? 

TA: In my view, OPVs will provide one piece to the puzzle of the future’s energy landscape. The size of this piece is not yet known and will all depend on future developments in the field of OPVs and the progress in other third-generation PV technologies such as hybrid perovskites.

I personally see OPVs being deployed in “niche” applications such as building integrated environments or where the ability to deploy the technology rapidly with minimal cost is needed. The emerging IoT ecosystem may also play a role. As the number of IoT-enabled devices increases, the need for self-powering capabilities increases. OPVs could well satisfy the demand and indeed provide unique solutions.

 

Hybrid Electronics: Combining Organic and Inorganic Technologies

AAC: What are hybrid electronics? 

TA: By definition, hybrid electronics can be classified as devices and systems where their electro/photo-active components comprise a combination of organic (carbon- and hydrogen-based materials, etc.) with inorganic materials (silicon, metal oxides, etc.).

For example, we often refer to state-of-the-art OPVs and OLEDs; however, if one takes a careful look into the actual device architecture used then we realize that there is at least one inorganic material involved, if not more. Therefore, many of the commercial organic electronics may well be classified as hybrid.

One such example is OLED-based displays where organic LEDs, containing a number of inorganic components, are integrated with inorganic thin-film transistors (TFTs) made of silicon or metal oxide semiconductors, to produce some of the best displays available to date.

 

A close-up of a sample OPV. Image used courtesy of KAUST

 

AAC: What do you think could be the most useful applications of these organic/hybrid soft electronics technologies?

TA: The ultimate aim of hybrid electronics is to marry the best of the two worlds: that of organics with the more traditional and established inorganic electronic technologies.

Organics offer tuneable electronic properties, processing versatility, and superior mechanical compliance. On the other hand, inorganic materials combine superior electrical performance, which is a prerequisite for many emerging applications.

Currently, not a single family of electronic materials can offer what is potentially accessible via the hybrid approach. This may indeed change in the future but right now the most efficient way of achieving optimal results is through a combination of organics and inorganics.

 

Future Research and the Impact of Renewables

AAC: You also work with biosensors at KAUST. What are biosensors and what are some of their possible applications?

TA: Biosensors can take many forms and find numerous applications. In my group, we are interested in developing inexpensive biosensor technologies in the form of miniaturized devices for use in existing as well as rapidly emerging technology sectors.

The present needs for biosignal detection are diverse and include environmental monitoring, security, and preventative medical care for point-of-care testing (POCT). The COVID-19 pandemic is an excellent example where POCT biosensors already play a major role (rapid test kits, etc.) in the future for the early detection and prevention of the disease. The challenge there is to develop technologies that are more precise, highly reliable, and, of course, cost-effective.

 

AAC: If countries are ever to achieve full reliance on renewable technology grids, what do you think the advantages—and possibly even potential disadvantages—of such a green infrastructure would be?

TA: The enormous advantages associated with future societies that rely entirely on renewable technologies are numerous, both for humans and the planet’s ecosystem, and need no further mention.

However, I am personally concerned when I think of how this future world would look like. Would the landscape around large cites be dominated by massive wind farms or solar farms? I come from Greece and, over the past few years, I have personally witnessed the dramatic impact of wind farms on the country’s landscape—both around cities, remote mountains, and islands.

Therefore, before covering our planet with renewables, we first need to ensure the best possible paths to implementing them at all stages, from point of generation to distribution all the way to point of use and end-of-life recycling.

Right now, I see the deployment of renewables being fully businesses-driven which partly explains the problem I highlighted above. Thus, I see the need for an increased level of regulation (at national and local levels) as the deployment of renewables continues to intensify.

 

AAC: What are your plans for future research and for the development of new solar and renewable energy technologies? 

TA: On the solar energy harvesting front, I am already thinking of technologies beyond photovoltaics. Although currently a purely academic exercise, we have every reason to believe that, if successfully implemented, our ideas could one day push the solar power conversion efficiency well beyond the current limit imposed by existing solar cell technologies, which for commercially relevant devices is limited to around 34%.

My interest is equally strong when comes down to solar fuels which I believe that in the not-so-distant future will help to transform the global energy landscape, from the way we produce the fuels to how we distribute, handle, and use them locally.

 

...our ideas could one day push the solar power conversion efficiency well beyond the current limit imposed by existing solar cell technologies, which for commercially relevant devices is limited to around 34%.

 

AAC: Last question. What aspects of your work do you find most interesting and why?

TA: The curiosity-driven research often pursue in academia is certainly the most interesting aspect of my work. Although some aspects of my research remain relatively unchanged, most of it continues to evolve, leading to surprises and often excitement. I will not change it with anything else.

 

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Many thanks to Dr. Anthopoulos for his time speaking with me and for helping us understand more about the mechanisms and potential of OPVs. 

You can learn more about Dr. Anthopoulos and his group's research by visiting the KAUST website.