Nurturing the energy revolution

​​Q: What first ignited your passion for solar technology, and what goals have kept you moving forward?

Prof. Martin Green: My journey into solar began in the early 1970s. The oil embargoes of that era led to a lot of interest in generating new energy sources. The US government launched a major initiative to fund alternative energy research. That attracted many of the world’s top scientists and created a highly competitive and intellectually stimulating environment.

We also got involved, and by the late ’70s, our small group in Australia was already doing things no one else could. That early success gave us a strong foundation. Despite being a relatively small team, we began to receive some of the most prestigious research grants.

Over the years, I watched solar energy evolve and become more feasible. When I first started, the only real application was for spacecraft. However, as technology advanced and costs came down, the applications opened up, from powering telecommunications and navigational aids to rooftop systems competing with the basic wholesale electricity generation costs.

Today, it is no longer just about producing clean energy, it is about ensuring access. The goal is that everybody can access clean energy and adopt this kind of solar technology globally.

​​Q: Your pioneering work in solar technology was recently honored with a clean-energy ferry named after you in Australia. How did it feel to receive such recognition?

Prof. Martin Green: It was a complete surprise, but a tremendous honour. I never imagined something like this would happen in my lifetime.

The ferry now operates on Sydney Harbor, running one of my favourite routes from Sydney to Parramatta, about a 20 to 30-minute journey west of the city. Interestingly, a science museum was recently relocated along this route, and the decision was made to name the ferry servicing it after an Australian scientist.

Someone must have nominated me, and I was fortunate to be selected. It truly caught me off guard, but it is meaningful. We officially launched the ferry earlier this year, and since then, many people have told me they have ridden it. That’s been very heartening to hear.

​​Q: This clean-energy ferry is one of many steps forward in promoting global solar energy. In your view, how significant is this moment for furthering the solar energy revolution?

Prof. Martin Green: It is hugely important, and we need to move faster than we have been because the signs of global warming are all too evident. In Australia, we have experienced massive bushfires, followed by widespread flooding that falls well outside the norm. It is a bit of a sign of what lies in the future. We’re beginning to feel the initial effects of climate change, which will only intensify unless we take urgent action.

That’s why switching away from fossil fuels, the main source of greenhouse gas emissions, is critical. Fortunately, solar energy has come of age just in time. Over the past 10 to 15 years, the cost of solar technology has dropped dramatically, making it an impactful alternative to fossil fuels.

​​Q: What role do international collaborations and governments play in scaling solar technology in the coming years?

Prof. Martin Green: We’re seeing efforts from governments like Australia, which is working proactively to accelerate solar deployment. Australia has set aside various renewable energy zones where they’re trying to concentrate solar and provide the transmission lines needed to get the energy produced into urban areas.

However, scaling up solar doesn’t just require infrastructure; it also demands a complete rethink of how electricity systems operate. Traditionally, the power has gone from large generators to homes. With rooftop solar becoming ubiquitous in Australia, especially in private homes, power is increasingly flowing from the homes into the electricity system.

Changes are required in the rules for how the system operates and is designed to accommodate the way energy generation is being transformed by solar. Australia can be a pioneer in that area because the uptake has been so strong.

International collaboration has already played a crucial role, and I expect it will be even more vital going forward. The exchange of knowledge and talent has enabled our research breakthroughs to influence commercial production in China, which in turn benefits countries like Australia that import these cost-effective solar technologies.

Looking beyond Asia-Pacific, I believe the next big leap in solar adoption must happen in Africa. The continent still faces enormous gaps in energy infrastructure. Solar, which is small-scale and standalone, can make a difference. These systems are helping over 500 million people access basic electricity for lighting and mobile phone charging.

Much of that progress has been made possible when costs have fallen thanks to technologies like PERC and support from international bodies like the United Nations (UN). One of the UN Sustainable Development Goals is to ensure access to energy for all by 2030. Solar systems are providing the most viable way of reaching that target. But we will need more support whether through increasing funding or a further drop in solar prices.

Pushing solar frontiers

​​Q: Beyond PERC, what other topics are part of your research interests? Which emerging photovoltaic technologies do you believe hold the greatest potential in the next 5-10 years?

Prof. Martin Green: Right now, I’m particularly focused on two exciting areas. The first one goes back to a theoretical paper I wrote about 40 years ago, where I looked at the limits on the energy conversion efficiency of silicon cells. At the time, most people believed that the efficiency limits lay just over 20% energy conversion efficiency. However, in my paper, I calculated the theoretical limit to be between 29% and 30%, significantly higher than what was commonly accepted.

That insight became a key driver for our research as we realized there was much more room for improvement. So we set ourselves a practical target of reaching 25% efficiency, which we eventually achieved. That milestone was reached around the turn of the century. The solar industry is now producing cells that are 25% efficient and getting close to that 29-30% theoretical limit I proposed years ago.

Back then, I thought it was just an academic exercise, unlikely to have all that much practical impact. But now that we’re so close to that ceiling in practice, I’m working with several companies to push as close as possible to the 29% mark. We may not reach it completely, but I believe we will see experimental cells exceed 28.5% efficiency.

The other way of improving efficiency is to stack cells from different materials on top of each other to capture more energy from sunlight. Sunlight can be regarded as a stream of particles called photons. Silicon cells respond to photons of all colors in sunlight, from blue to red and even to the lower-energy infrared ones that our eyes can’t see.

The cells convert the photons in sunlight, but they don’t care too much about the exact energy of a photon as long as it is above a certain threshold. They just get electrons generated by the cell when the energy of the photon is high enough. However, blue photons contain much more energy than needed, and in standard silicon cells, that excess energy is wasted. It is one of the reasons that the efficiency of silicon alone is limited.

But if we stack a second cell, made from a material optimized to convert those high-energy blue photons, on top of the silicon, we can get an overall efficiency advantage.

One material showing great promise in the laboratory now is known as perovskites. It is a special perovskite made with heavy elements like lead and iodine. Most perovskites are made from lighter elements, but this one has unique properties because of its composition. There’s significant interest in stacking these perovskites onto silicon cells, and lab results are already very close to 35% efficiency. Naturally, there’s strong commercial interest in this approach.

There is another issue. Although silicon is stable, these specific perovskite materials haven’t yet demonstrated stability anywhere near that. As a result, working on perovskites has become a central focus of ongoing research. In fact, one of my colleagues in our team just set a world record for perovskite cell efficiency, 27.3%.

However, perovskites may never achieve the threshold needed for widespread commercial use. That’s why we’re also exploring alternative materials. While none of these candidates currently match the performance of perovskites, they may have the advantage of better stability in the long term.

​​Q: Would you find this the most promising path for the large-scale deployment of the solar revolution?

Prof. Martin Green:  Absolutely. Efficiency has been a key driver in the dramatic cost reductions in photovoltaics over the past few decades. Some studies even suggest it is the biggest factor, although I believe economies of scale, the volume of production and all that has gone along with the industry’s development are probably just as important.

Still, by improving efficiency, you can reduce the volume of some materials, transportation and installation work needed for a given energy output. That’s why every manufacturer today is laser-focused on squeezing out every bit of efficiency possible from their commercial products. If we can transition to one of these stack cells, like perovskite on silicon, it could revolutionize not only performance but also system-wide cost dynamics. Not so much in the cost of making the cell, but by leveraging those efficiency gains to reduce the broader costs of solar deployment.

​​Q: How do you view the integration of solar with other renewable technologies, including green hydrogen or battery storage systems, in creating a resilient and low-emission energy future?

Prof. Martin Green: That’s an essential part of the picture. There is a certain complementarity between solar and wind. In many regions, wind power tends to peak during winter and evening hours, when solar production is low or nonexistent. That natural synergy helps reduce the amount of storage needed in the grid and ensures a more balanced energy supply.

The partnership with batteries has also played a vital role, particularly in managing peak demand, which typically occurs in the early morning and evening. Solar energy is not at its strongest at those points in time if it is available, yet demand is high because of daily human activities, including cooking, lighting and showering. Batteries help bridge that gap, shifting energy produced during the day to those high-demand windows.

​​Q: The integration of clean energy technologies into existing infrastructure poses significant challenges. What are the key technical and economic barriers to widespread adoption?

Prof. Martin Green: Bringing down the cost of cell production is obviously crucial to expanding the interest in using them. According to the International Energy Agency, solar power is delivering some of the cheapest electricity in history. The exciting thing is that the cost of solar is still coming down despite the massive decreases we have seen over the last 15 years. It continues to fall week by week. So we’re going to see extremely low costs, and some people are even talking about a third energy revolution.

We witnessed the agricultural revolution and then the industrial revolution. Now, many believe we’re entering an energy revolution, where it becomes so affordable and accessible.

That’s why we’re pushing hard to make the cells more efficient to tap into these cheap materials. However, one of the biggest near-term challenges is finding a cell that you can use in these stacks. Silicon is an ideal material for photovoltaics as it is abundant, non-toxic, and remarkably stable. What we need now is a complementary material that shares those qualities but with added performance.

Perovskites have achieved good efficiency, but their reliance on lead, a toxic heavy metal, presents other issues. The goal is to discover materials that avoid toxicity, offer high stability, and are based on earth-abundant elements.

The development of AI will provide a much wider scanning of possibilities than the approaches we have been using. The whole material system can be canvassed, and perhaps some new materials will be identified. I’m expecting to see lists of candidate materials popping up, some of which might work well in practice.

The potential of Vietnam

​​Q: Vietnam has demonstrated a strong commitment to renewable energy, as seen in the transition’s efforts to green electric vehicles by VinFast. What opportunities do you see for Vietnam to emerge as a leader in clean energy adoption in Southeast Asia?

Prof. Martin Green: Vietnam is probably already leading Southeast Asia in the clean energy transition.  In terms of photovoltaics, the data I have seen suggests that over 10% of Vietnam’s electricity has been generated from solar in recent years. As the adoption scales up, the uptake needs to match the electricity network’s ability to absorb solar power. That means investing in battery storage and other technologies to stabilize the system, and it seems to be going very well.

What’s also encouraging is that Vietnam now hosts several photovoltaic panel manufacturers. So I think Vietnam would be one of Southeast Asia’s leaders in terms of photovoltaics.

On the mobility front, I was impressed by VinFast’s electric vehicles when I visited Vietnam in 2023. The quality of the cars seemed like genuinely competitive products. I also like the electric buses that VinBus has developed in Vietnam. Electric scooters are also incredibly important in Southeast Asia, where two-wheeled vehicles dominate the streets. China, for example, has shifted from fossil-fueled bikes to electric ones. That change has made a noticeable difference in pollution levels and CO₂ emissions. If Southeast Asia can follow China’s lead in switching to electric two-wheelers, it would be a significant step forward. In this context, Vingroup seems to be leading the way in developing vehicles that can meet this potential demand.

​​Q: Since joining the VinFuture Prize Council, you have had a unique perspective on the contributions of VinFuture and Vingroup to Vietnam’s green transition. How would you evaluate the impact of these efforts in nurturing groundbreaking science and accelerating global sustainability goals?

Prof. Martin Green: The VinFuture Prize is not limited to clean energy; it is designed to honor innovations with global impact across a wide range of disciplines. Past laureates have made groundbreaking contributions in medicine, agriculture and many other fields.

That said, my involvement in the council has allowed me to connect with many experts in related areas. This has been incredibly valuable. I also shared the 2023 prize with Professors Stanley Whittingham, Akira Yoshino, and Rachid Yazami, whose pioneering work is in lithium-ion batteries. It is a complementary area to solar energy that I have been working on. Meeting those people and getting to understand their contributions better has been really important to me as well.

​​Q: Your groundbreaking invention of solar cells enhanced by Passivated Emitter and Rear Contact (PERC) technology earned you the prestigious 2023 VinFuture Grand Prize. How has this award supported your ongoing research and fostered new collaborations?

Prof. Martin Green: One of the most immediate outcomes was the opportunity to establish new collaborations in Vietnam. I have gained much greater insight into the progress being made in Vietnam’s clean energy sector than I knew before.

The award also introduced me to many of the world’s leading researchers and scholars in various fields related to clean energy through my involvement with the VinFuture Prize Council.

Another key benefit has been the increased visibility and media coverage, which has helped boost support and funding for our research group. Securing research funding has been one of my prime jobs for over the last 40-50 years, and winning such a major prize has certainly enhanced our ability to attract the resources needed to develop new ideas. It has been a significant and positive ripple effect.