 Yeah, so I'm Le Tendo, Associate Professor in Chemical Engineering. It's my great honor to moderate this panel discussion. First of all, I think everyone enjoyed the great lectures a moment ago by Professor Tai Sajin. So I don't need to introduce him again, so I will skip that. But let's welcome our main panelists again. And now I would like to spend a few minutes to introduce the rest of the panelists. So we have a very diverse and young and energetic panel here. So first is Professor Arang Manudi Kanakisadi, hopefully my pronunciation is correct. He is a assistant professor in the School of Materials Engineering. And his research interest is novel materials discovery through high throughput density functional theory and machine learning. And he is also very active in searching new high light per-scale materials for solar cell and optoelectronics devices. He joined Purdue about two years ago. Let's welcome him. And next is my colleague, Professor Bracevoi, who is currently the Charles Davidson Associate Professor in Chemical Engineering. And his research interest is computational method development for materials design, property prediction, and degradation mechanism studies. He is a leader, a PI of 7.5 million DOD-founded MURI program here, and he is actually studying the degradation process of organic materials, post-scan materials. Let's welcome Professor Voi. And next is Professor Peter Bermond, he is currently the Elmo Associate Professor from School of Electrical and Computer Engineering. His research interest is improving performance of photoattacks and microelectronics using nanophotonics principles. And he is also a leader of a big center, a big effort regarding scalable asymmetric life cycle engagement macroelectronics workforce development program. Sorry the name is pretty long, I have to use this. This is a multi-university, a big project led by Purdue by Professor Peter Bermond. So let's welcome him. And last, not least, Professor Shubra Bansal. She is currently an Associate Professor in the Mechanical Engineering, a School of Mechanical Engineering. Her research interest is porous guide, trachotinides, and 2D materials, semiconductor materials. And she is also expert in interconnects and electronics device integrations. She was Associate Professor in the University of Nevada in Las Vegas, a very fun place. And she just moved to Purdue a few months ago, but unfortunately this week she's out of town, but she kindly agreed to join the panel virtually. So let's welcome her. Can we see? Thank you. Okay, so that's all the panelists for today. Now let's get started. So to get this started, I prepared a few simple, naive questions. Maybe some of this point has been touched upon by Professor Ted Sergent during his lectures, but now we have more opportunities to dive into more details on those topics. Probably we'll spend 20 to 30 minutes on three or four questions, and then we'll open the floor to the general audience. I hope, look forward to more interesting questions from the audience after that. Okay, so first question is, so over the past several decades there has been several waves of photovoltaic research. However, the implementation is quite slow, so we haven't had too much solar panels in our daily life, but now recently the silicon panel cost has become low enough, and the post guide provides additional very exciting opportunities for the lower down the cost. So the question is, do you guys think PV technology will really start to play a major role in our society? For example, by producing really generating 30-40% of the energy for our daily life, and to realize that, except for searching for new, better materials, what are the current major obstacles to realize that goal? Probably I'll ask Ted to start, and then Peter and Shubra can follow up. Actually, I think we should start with Peter. Peter looks like he's got a lot of original things to say compared to... No, I think it's on already. I think it's on. Okay. Yeah, I think it's on. I think we should start with Peter. I've said a lot of what I have to say on this. Let's go to Peter. Alright, so thanks Ted. So first of all, photovoltaics is absolutely crucial technology. I'm in full agreement 100% with Ted. And I think that future belongs to photovoltaics. It's such a fantastic opportunity because there's so much power available through the sun. And we are at the point now where it is actually having like increasingly large impact on society. It's been growing exponentially for the last 10 years or more since we kind of reached what some people have called the grid parity regime where the cost of installing new solar was comparable to the cost of installing or even in some cases maintaining other types of conventional fossil fuels. So it looks like the future is bright for PV, but there are some major challenges as well. So one of the biggest challenges going forward will be finding ways to accommodate more and more solar energy on the grid. And so that means like finding ways to use solar power effectively. And that includes having a grid that can support kind of variable generation. And we already have ways to do that. So it is possible to do that just to be clear. And there are some places where solar is actually like a very large fraction of the total energy mix. So we're well below that now in most of the United States, but certain locations like Hawaii are much further along than Indiana, for example. Partially because they have more solar resource, but also because the cost of alternatives was higher. So they reached grid parity earlier. But we are at that point now in Indiana and many other places throughout United States, North America and worldwide, where it will make more and more sense. But then the second thing beyond the grid challenge will be the question of land use. And it will be important to find land areas that can productively accommodate solar energy, while also supporting their primary original goals. So that includes not just urban areas, which is actually not a huge amount of area if you just look at rooftops, but also could include other parts of the urban infrastructure, could include areas that are near cities such as agricultural lands, and also other types of land that can accommodate the potential for solar energy. And then another thing that will be obviously very critical is to provide better ways to utilize solar energy in a wider variety of uses. And so that could include some of the solar fuels initiatives that Ted was talking about, but it could also include greater electrification of existing applications that we care about, including transportation. Thanks. Peter, that was an astonishing answer. I just want to compliment my fellow panelists here. Very comprehensive. No, I'm being very serious. I don't really have much to add. I'm the computational person. But I think that I was just going to kind of piggyback on the finding creative uses for it as well, because there are formidable infrastructure challenges to accommodating photovoltaics. I think on the long-term horizon, there's just so much net potential in photovoltaics that it's bound to happen. It's a when, not an if, but there will possibly need to be incentives to close the gap as soon as we want to and as soon as we need to. But the applications that don't necessarily have to have you on the grid are also kind of compelling if you could couple it to chemical production so that you could store it locally or put it to innovative uses that could help address these load-leveling issues. That could also be very advantageous. Yeah. I can make a couple of quick comments. I mean, yeah, that was pretty comprehensive from both of you guys. I'm also a computational person. I'd make just one general comment and one specific comment. The general comment would be about further incentivizing the use of it, which also was touched upon just now. But obviously, the costs have lessened over the years. There's now a lot more availability of solar power. So maybe just more people, the more people start using it, the better it would be. But I wanted to comment something from the computational perspective, which is in terms of, I mean, of course, search for better materials is always, we are doing that all along. There are a number of things where fundamental computational simulations, atomistic simulations can still help, I believe. So there's a lot of things that we can still understand, like ion migration or defect tolerance in these materials. So I'm sort of bringing in specific things that I like to do. But just in terms of materials that are already being used, perovskite solar cells or cadmium telrytylated solar cells, there's still, although it seems like it's a saturated field, but there's still a lot of work going on in studying kinetics and activation of dopants in cattle, for example. How does ion migration happen? Interfaces, what's going on at interfaces? So I feel like if we can further improve the theory more, this would involve creating new force fields, for example. Machine learning comes into the picture there. We typically use density module theory simulations, but it's expensive and the level of theory is important, etc. So in terms of, this may not directly contribute to PV technology being in everybody's homes tomorrow, but I think there's a lot more fundamental work still to be done and funding structures can incentivize that as well. So I think we can, from first principle simulations, molecular dynamic simulations, improve the level of theory that we can use, improve the capabilities in terms of the properties that we can study, the effect of defects, interfaces, mixing and matching between known materials, like mixed chalcoginite and perovskite together, maybe. I don't know. So things like that are what I think computations could maybe help with, as well as data science or machine learning-related techniques, which I'll talk about it a little more in the next few questions, I think. Yeah, great. How about Professor Bensow? You have any thoughts? Good point. And then you want to summarize. Maybe I'll just see if I can ping Peter on something. There was a number, but you might have the number. In the last couple of years in southern Germany on a sunny day, solar has been meeting like a fairly high fraction. Maybe 40 or 60 or something percent of total demand. And Munich didn't catch fire. The place didn't blow up, you know. And so I'm not to say that there isn't more work to be done on the grid, but there is. And I'm sure we should work on it. But there are certainly, there are locales that have been instantaneously receiving a large portion of their energy from solar and have been able to manage it. Yes, that's correct. And I believe that there are even like instance and time where you have the total production of power is matching essentially all the short term power needs. And obviously this is a moment to moment thing, so that doesn't mean that like Germany is 100% solar overall. But it just means there are certain locations at certain very specific times a day where that's happening. And that's really interesting development that that even can happen. And so you actually get to the point where you need to think about either transporting or storing solar power because you're generating so much power. So that is going to be like one of the key challenges in terms of the grid. How do you deal with that? Yeah, yeah, grid points. Yeah, so maybe it's time to move to the second question. So the second question I have is, so the world is very excited about here like ProSky. So the question is, is ProSky the real future for photo tag? And are we really, they could just put too much excitement on that or this is really the promising future. So kind of stability and the manufacturing issues being resolved on the ProSky technology. In your opinion, what do you think in the next five to 10 years, will this happen? Want to go first? We have a few people working on ProSky. I mean, I don't think I should go first, but I might as well. So I mean, that this was already discussed. I'm not the most qualified person to suggest to talk about its practical usage or when it will actually start being deployed. Once again, I mean, I assume I'm here as the computational or machine learning person. So I can comment from that point of view. I think in terms of, I think ProSky's are definitely the future, but there's probably a lot of shortcomings. I mean, the stability, of course, right? So I feel like there's again a lot of things. So personally, we are trying to do a few things which can help address it, right? Which is ways to address the stability. Can we come up with possible degradation mechanisms? Can we come up with ways to predict, like a halide segregation or phase segregation? Again, it comes back to the improvement of theory itself, like, you know, to make these predictions better. But, you know, I also want to mention that we have been focusing on making more ensemble predictions rather than giving you one prediction for a property, which means that, you know, there's a range of properties that a material can exhibit based on which, you know, phase it could exist in all the metastable phases. There is a tendency in zero Kelvin DFT, for example, to give you that, you know, here is the optimized structure here of the property. So we are focusing a lot more on creating, like, instability, using instability as a factor itself. So I feel like, you know, if we use that in terms of screening as well, we can further improve, like, you know, the scope, like, you know, properties that we have. We may not have exhausted the possibilities, like, you know, the attractive properties that we can achieve from already known materials itself. Are there ways to better mix and match them? You know, are there, is there, like, you know, some, you know, other, you know, metastable phase that we are missing, et cetera? So that is one thing that I wanted to talk about. In terms of, you know, the practical usage, when can it be deployed? What is the future? Like, you know, I hope there is a bright future. I think we talked about it a little bit before. You know, tandem perovskite solar cells are, you know, hopefully the way to go. If we can accelerate the prediction of, you know, like Professor Sarjan said, like, you know, we can, without using let-in perovskites, can we get, you know, low-band gap perovskites which are very stable, do not, you know, phase segregate, blah, blah, blah, without doing iodine bromine mixing, can we get high-band gap perovskites which are defect tolerant, for example? So we do a lot of work on defect tolerance, you know, for example, like, you know, can you, can you design these perovskites in such a way that defects are not going to form spontaneously and, you know, affected properties, or you can put in functional defects or dopants, et cetera, right? So that's my perspective on it. I hope there's a bright future, and I would like to contribute in, you know, in newer, fresher ways, if possible, you know, based, bouncing off on ideas from everybody, probably. Yeah, I totally agree. So from a materials chemistry point of view, there's stability and the processability. They are conflict with each other. If you make things more easy to solution process, you decrease the strength of the boundary and you increase the stability issue. So is there a way to go around that? Maybe, Brian, can I think about this? Are you on comment? Yeah, I would just, I would strike a very optimistic note. So for those of you who haven't followed the perovskite closely, I mean, it's really unprecedented in terms of how rapidly the efficiency has risen, and we are, we've barely scratched the surface in terms of stabilization techniques that can be deployed. So it's very early for a materials platform to be so seriously considered as a translational technology. So I think it's, I'm extremely optimistic about perovskites. Yeah, the fact that we're having this conversation is kind of astonishing. Coming from a field that, I won't name the field, but where I did a lot of my PhD work, things had moved so slow and I was entering it, it was already, already had about 20 years of inertia behind it, and they were barely starting to have those kinds of conversations that perovskites have been having. So I'm very optimistic. Thanks, and Professor Bonzo, you have any comments in terms of the mechanical reliability and stability side? Yeah, thanks for the comments. I totally agree. The light is magic, but if you find another one beyond light, that will be another big, big breakthrough in the future. Okay, so first of all, perovskites are an amazing technology and they're amazing people working on them. So I want to be very clear about that. I'm very impressed by the perovskite research. I would inject a slight note of caution in the sense of like, will perovskites directly replace incumbent technologies? I don't want to predict that right now, but I also don't want to not predict it. So in other words, I think it's going to be an open playing field in terms of materials, and I do think that what will be important for perovskites to be commercially adopted is to offer competitive advantage that existing technologies cannot. So that's where the tandem approaches are actually probably from a commercial perspective, the most promising, because that gives you higher efficiencies than you could ever get from just a single junction design and potentially at a cost competitive price. And so that's really the key to make it like actually still be cost competitive with incumbent silicon technologies. It can't be like an order of magnitude more expensive if you want it to be widely deployed commercially. I would add another thing though, which is it's not just about photovoltaics as much as we all love the photovoltaics, but there are a lot of other interesting projects in terms of using perovskites for other types of photonic devices like lasers, LEDs, etc. And that could actually be the lowest hanging fruit for perovskites where they offer a real advantage in terms of performance and cost, and could actually tolerate slightly higher cost of encapsulation and stabilization compared to PV technology. So that's something I would encourage a lot of the researchers there to think about. You mentioned the lasers, LEDs, maybe I thought about that. So you have beautiful work on LEDs and photonics. So what do you think on solar cells and also on other applications, what's your opinion? Yeah, on the LEDs we've worked on a few colors, but I guess I'm particularly excited if we could produce a blue LED that was just the right wavelength, 467 nanometers, was reliable, achieved an EQE of 18 or 20%, and had a very narrow emission line with perovskites, because then we would fill an unmet knee that's not currently being met with the quantum dot technologies. The quantum dots are doing meaning most of those specs pretty well in the green and the red, but not yet in the blue. So we're very interested in whether we could contribute in advance using perovskites in that context. I do worry about the abilities, even worse in the LEDs, that the challenge is more significant. Yeah, I think that's a fair point. As you and I were discussing a bit in your office today, Latina, I feel there may be a reason for that related to the fact that we haven't got the contacts quite right yet. There's enough evidence that the excessive voltage currently needed to drive perovskite LEDs actually, especially the blue ones, might be attributable to some kind of local energetic barrier that we may be able to remedy with a better use of hole injectors. So you're right, the stability is far from where it needs to be. I think we may be able to find the implements to address that. More effort needs to be devoted into that. The comerva solar cell LED is much smaller community. Great points. Yeah, let's move to the third question. Maybe after that we'll open to the audience. We can have more questions from the audience. The third question is what are the best ways to handle the electricity generated by PV? Daddy, you mentioned the electrolysis CO2 reduction as a way to store the energy into chemical fuels. Maybe you can also store it in a battery or directly use electricity. What are the challenges towards those different directions? I think there are many other ways, better ways or more creative ways to utilize the electricity generated from solar. Okay, I can start. So there's a lot of opportunities here and a lot of it in my opinion in the short term is going to be about electrification of many of the things that we do day to day. Particularly things like transportation like replacing some of the fuels with electricity like battery storage. And that is something that's a proven technology. However, there is a consumer challenge at the moment which is do people feel confident about buying particularly like plug-in hybrid or just pure electric vehicles if they think that they need to take long trips? And maybe 90% of the time they don't but the 10% of the time they do they really care about that issue. So being able to extend the range of innovations in battery technology will also have synergistic benefits for photovoltaic adoption I believe. And there are a lot of other scenarios and cases like if you think about lawn mowers and many other things that use liquid fuels there is potential for electrification. At the same time I do think there is long-term potential for solar fuels as was discussed. I think the biggest challenge there is to bridge the efficiency gap between electricity to battery versus electricity to solar fuels and also to make it cost competitive but if you can do that obviously there is going to be a lot of adoption. And there are certain technologies such as for example like jet fuels where you are never going to replace like a long distance, long haul jet flight with a battery at least I don't see how that could happen. So you would expect that especially those kind of markets will have like adoption of solar fuels first if anybody is going to adopt them. Right? I think that well the other half of my research is on batteries and it's sort of for a reason because it's a so batteries are they are similar to what we have been discussing with Probsky Research because there are so many fundamental challenges when it comes to storage. There is still a lot of unresolved chemistry fundamental knowledge gaps. At the same time there is this huge relevance right? So you know lithium ion technology has decades of research behind it and it's not going to solve grid scale storage and so we have to learn to do what we did over decades with lithium ion technology for you know sodium and for more scalable battery chemistries. I was having a conversation with a battery company about the context of fluoride ion batteries. So we're interested in fluoride ion because they potentially have very high energy densities and they were sketching out the roadmap and they were saying that you know if everything works like the electrolyte that we've developed if let's say that checks all the boxes moving down. We have no further materials development and they're saying that the soonest that they would be envisioning adoption would be 25 years. Based on all of their scale up they were estimating you know all the challenges that would inevitably happen with scaling up and with sort of reaching the kinds of storage capacity. So I think we have to work really hard on accelerating that time scale and it's not a real attractive problem but I think it's a very important one on speeding up that translational time scale. Thanks for the good points. Yeah, I can make a quick comment. One of the avenues I thought was interesting is the hydrogen energy storage route where it seems like there's a lot more funding coming in that direction like the DOE hydrogen program and stuff. So since like Ted mentioned in his talk too there's been a lot of work done on water splitting I have done some work in the past so the same techniques that we're using to discover new absorbers and stuff like that can be used to discover new catalysts for water splitting and then you need good materials for hydrogen energy storage and then you need to re-electrify it etc. So of course there are challenges involved in that but I think that is a promising direction that's something we've been thinking about my depth of knowledge is not too much more in this topic but apart from the electrochemical energy storage I think the hydrogen avenue worth pursuing computational screening can be used there as well effectively I think. Actually we have expert on electrochemistry here in the audience maybe he can comment later after the Yeah please be free to comment. Yeah and Professor Manso you have any comments? Well I agree with whoever pointed out the round-trip efficiency of batteries is impressive and a little hard to beat I mean to the point that solar fuels people don't talk about their round-trip efficiency so yeah I would say that for you know as Brett was saying grid scale storage we need to think of really scalable dirt cheap battery solutions based on earth abundant materials and it's a pretty it's a pretty urgent and important area for all the reasons these folks have said. Great and Brian you want comments? Okay so ahead of the schedule so maybe I was through in my last question since Brett mentioned even one like a simple fluoride battery takes 25 years in ideal scenario then my question is will the carbon neutral future go realistic or not by 2050 so what should be achieved along the way like in the 20s for example 2030-2040 what should be achieved to make us on track and how we can contribute as a scientist or engineer over a big picture question. You know it's a big challenge to be carbon neutral especially if we just continue with the status quo in the United States I don't want to speak for other countries but United States is not on track for carbon neutrality in 2050 unfortunately. Now with that said that's not a complete like we aren't there yet we still have 28 years but things have to change quite a bit to get there I think like one thing that's very critical to be aware of is just the energy industry is often times investing for decades out into the future so that means that if people are building natural gas plants or other types of plants today thankfully they're not building as many coal plants but they are building lots of natural gas facilities too and those are going to be expected to last 30 years so you have to have first of all a path to deploy enough solar energy, wind energy or some other sort of renewable energy to replace all that capacity so that's number one but then number two is you have to have some sort of decommissioning plan or way to accelerate like the phase out of these plants and then you also have to have a way of addressing the shareholder concerns at all the energy companies that may not be happy if we go to a carbon neutral future so there are a lot of like practical and political challenges this is above my pay grade just to be clear but I'm just saying we need to be aware of that with that said though I think the best thing we can do as scientists and engineers to contribute is to find practical solutions in the context of renewable energy that can be scaled to meet our needs such as like low cost high performance photovoltaics very high performance storage solutions like both on the battery and solar fuel side and then also like innovations in terms of the power infrastructure including the grid that enable both the transmission and storage of energy that's generated through these renewable pathways and then finally we need like more creative solutions of how we can use solar energy for a lot of the things that we want to do day to day and of course transportation is a huge user of energy but anything in the household anything that we're doing that currently requires either fuel or batteries or whatever is a potential candidate for solar adoption so we should think very creatively about that and that's something that can start even at the undergraduate or high school level so we want to start right away Great. Who wants to be the next? Oh yeah. Thank you. Thanks Brett. I will just pick up on the seemingly very memorable chloride battery example that Brett surfaced and just say that I think a lot of those 25 years are going from when we've totally locked down the science that actually works we've built something small scale and then we actually work out all of the many many kinks related to reliability, manufacturability scale etc so while I don't have the solution I will pose the problem which is how do we once things have actually already reached a really advanced demonstration stage how do we pull them through faster towards scaled market impact I'm not sure I'm the kind of person who could even contemplate how to answer it it seems like a question perhaps for business schools maybe policy people as well some folks interested in manufacturing and scale manufacturing maybe industrial engineers but I just want to highlight it as a a critical question I guess if you want to say something encouraging it might be that I doubt there's any sort of fundamental kinetic barriers to accelerating that process probably there's a lot of money involved somewhere in there but more than just money I mean a very intelligent deployment of incentives to try to accelerate adoption thanks right I would actually borrow Peter's comment from earlier that I'm not going to predict what's actually going to happen between now and 2050 but assessing my own role as a scientist and engineer in society I view my job to provide you know technological solutions and to remove excuses right so it's always easy to punt if there's no technological solution well technology's not there technology's not there when you actually you know deliver the technology you say no just there's a will is what's required now that's what I think our role is to get the fundamental work to that point and the engineering to that point so we'll see what what happens we can have this conversation in 2050 and see what happens okay well excellent points raised here my opinion on carbon neutral in 2050 is that I personally am not that optimistic about it it doesn't look like you know the goals are going to be met but you know if we can move you know we can move in the right direction that's still something my feeling is that you know the fundamental research that we are doing while excellent is not you know directly contributing to these lofty goals which have to be achieved through policy changes which have to be achieved at a much large scale I'm not the best person to comment on that but you know from from where I'm standing I think you know probably a lot more needs to be done on an on a national international global you know scale you know through policies I think like you know like infrastructure bill and things that were passed is all you know in a step in the right direction but probably a lot more needs to be done right I mean I was having a discussion with a colleague today I was always hopeful that the US would have invested a lot more on public transport for example right wouldn't it have to be done on public transport it's just the kind of thing that's never going to happen I think because you know like like China has high speed rails you know etc but because of the you know just the way the rail system was developed in the US I guess I mean it's going to take trillions of dollars right so is that's probably not a direction we'll ever pursue I mean I wish we could but you know so simple things like you know have more public transport so that you know people aren't you know driving so what we change we make is everybody has an electric car I mean you're probably not going to use an electric car to do a long drive so you know so then maybe you're going to fly more so you know so then you know those are problems as well so this is you know I'm just speaking as a person more than a scientist here or you know more than a researcher but to me it feels like you know probably a lot more needs to be done but you know some things are you know there are some things to be optimistic about that could help you know I think probably that needs to be one focus at least yeah I totally agree policy is important but my question is policy is more important or I'm taking a side do we need a really like a breakthrough theory like a relativity or quantum mechanics or we can just just build everything that would help you know if you can find a boundless source of energy sure that would be great I don't think there's any thermodynamic limitations on us achieving it it's I think it's a technical challenge you know agree yeah and how about Subaru Subaru we have a technology technology great yeah so that's all my questions now the floor is open right Brian thanks thanks for the discussion so related to maybe not directly what Leitain was asking but the way that you all answered that question so we've seen recently a lot of funding support for these problems and these large scale and very urgent problems so my question is how important are the people who direct the distribution of these funds you all at some point mentioned in policy should we be sending a lot of our talented engineers to Washington the people who know about these problems and understand the technical aspects should we be training them at least a little bit in policy and sending them in that way so that's that's one question a sort of related question is you know we all as academics understand the importance of basic research with such a large scale urgent problem should we also think of a broader type or even larger than center scale research to try to really go after a problem from start to finish and shrink that 25 years down so you asked two very difficult questions but I'm happy to answer them so the first question there's not necessarily a one size fits all answer but I would say the federal government particularly like Tony Blinken when campus recently noted that is very important to expand the government ranks to include a lot of people with talent in science and engineering so while this not necessarily something for everybody I know there are some students who really do have passion for policy and working in the government sector and I can just tell you your talent is needed like like you do need to obviously understand something about government you shouldn't just go in cold as a pure tech person but it is important to have that tech background because more and more of the issues we're facing will require a sophisticated understanding of the technological and scientific challenges that we're facing so I would say I'm generally supportive of the direction you're going here and then the second point about like creating bigger and bigger centers and kind of having those aligned you know in terms of the government people and people within academia I would say you need like to solve like these major challenges you need like a actually a global cooperation framework ultimately and then that also requires coordination at the national scale and across universities as well as like the private sector and the public sector so you basically need all hands on deck solution if you view these as like really major challenges if you don't then obviously you don't but I think like if you said like our goal as a society is to achieve the maximum decarbonization possible by 2050 it is an all hands on deck effort Any other comments? So to have more questions from the audience so probably we don't need to go through everyone if you want to stress you just go ahead if not we just move forward Yeah I can make a quick comment I think the policy question is I think it's very important I think we should focus on that like personally me during my training as a scientist I knew very little about what actually constitutes a policy probably still don't I read a New York Times article that's how I know what's going on in Washington so I think we should emphasize that I mean I'm not sure if we can incorporate that in the curriculum itself but I hope there could be ways of doing that through seminars, minors I would also emphasize the importance of humanities there as well I think we don't just want to train excellent material scientists or chemical engineers but the policy decisions that would be the most effective they should have an idea on how to go about doing that they should also know things like which are the most affected areas by climate change and what can we do to instantly help them like things like that so I don't know what the best solution is but I would emphasize it's very important I think that's a great point I'll make a very quick comment because very interesting question Ryan and you're talking there's a conversation amongst academics but academia isn't always the best configuration it has its own incentives that aren't necessarily conducive to solving a problem like this like to take the battery example or photovoltaic example and you know people make analogies with moonshots we use that phrase like the Manhattan Project we don't ever really you know like the Manhattan Project people disrupt their lives to all move to a centralized site to accomplish just one goal and I don't know the center is kind of a halfway point but even the center itself is also within an academic context so I think we have to ask questions about if funding academics in sort of small team medium sized team fashion is always the best way to do it but I think people are getting creative on the funding side so you're starting to see more cooperation, very large scale funding mechanisms but it's still in its infancy I think Thanks, thank you let's get another question before we run out of time let's go to the next question yeah let's go Professor Lam and obviously we'll be next So I'm an electrical engineer I want to ask a question about this the viability of tandem tandem was originally developed for space application when the intensity you can have the intensity more or less constant but in a solar farm, terrestrial solar farm the sun moves throughout the day and the current matching problem is such that you can demonstrate that at the end of the day single junction is always better than silicon perovskite tandem in terms of efficiency because of this current matching issue and also silicon is a thousand times thicker compared to perovskite and so therefore even a small variation variability leads to a significant drop in efficiency so I don't fully understand maybe you can explain a little bit more that this focus on two terminal tandem is it coming purely from thermodynamic considerations or actually there is some underlying calculations or predictions for terrestrial conditions that makes it a viable solution again tough question so I turn to Maxberg actually I think I'll invoke other experts but my understanding is that the analysis of tandem looking under real terrestrial conditions does actually have them providing an energy yield benefit whether they're using one-dimensional tracking I'm not sure but I wonder if that's maybe the resolution that you need simple tracking but simple low-cost tracking to achieve the energy yield benefit but my understanding is that you do achieve a statistically significant benefited energy yield in the tandems and that that's got field measurements behind it and it also has predictions based on real world solar arcs and even spectral variations built into that yeah so that was my understanding as well but I agree that fixed tilt is going to be a problem so you probably need at least single-axis tracking for this to be viable but then the other thing that's important to note is that there are some variations on the two terminal tandems such as four terminal tandems and other approaches to current matching that are being explored currently and so like including the three terminal systems I should say like there was some work at NREL recently on the three terminals and so these are like basically different ways to try to address some of that current variability issue that has like obviously been challenging for the field not just because of day-to-day spectral and solar intensity variations but then also because of potential degradation on the perovskite so I think that this is like obviously a key area of research to make perovskites potentially commercially viable to have like kind of a long-term stable solution so you won't have to like reapply a new perovskite every couple months or something yeah great so let's move on to the next question I have a question about stability of this perovskite I don't work on the photovoltaic but I work on other products like the hydrochemical device system I know like if that that's the ability because of some dynamics or kinetics that they're doomed we cannot do that because if that's because of engineering problem then they maybe can solve so my question here is maybe probably for the modeling part you can calculate some dynamics and kinetics do you think that is stable, some dynamics or just the degradation too fast or still don't know yet I don't think that the perovskite is intrinsically it's not metastable so I don't think that there's fundamentally any reason why we can't stabilize these things that being said Latine was alluding to the fact that the ease of processability the fact that this is an ionic solid means that there's a susceptibility to certain stressors like water so but we still are looking into strategies like we've been shocked for instance by putting down a monolayer of something can have qualitative impacts on water susceptibility and ion diffusion and this is very early in research so anyway again I don't think I can certainly answer that there's nothing fundamentally thermodynamically unstable about the materials but they do have some intrinsic susceptibilities that have to be addressed yeah I mean computationally when we look at the stability of you know just a perovskite crystalline structure we probably only look at you know which phases will it decompose to what is the enthalpy involved in it maybe we can you know do some entropy you know things like configuration entropy vibration entropy etc but you know maybe there are limits to you know what we can predict from computations like you know it may be predicted to be stable but there may be pathways that we are missing I think it's also important to take defects into account at that point like you know which a compound may come out to be you know stable against decomposition but you know there may be certain you know point defects that could form spontaneously so there are ways in which simulations can help address that but yeah but I agree that you know it's not like an intrinsically unstable material but there are ways in which it is you know thermally or mechanically or you know photo stability is bad or you know things like that so not all of that can maybe be addressed you know using certain you know using first mental simulations but there are ways in which we could maybe do one level of screening where we eliminate ones that are obviously going to be you know to you know decomposition to constituent highlights for example or something like that yeah great last question be brief please well thank you all for a great discussion thank you all for a great discussion so far maybe one last big picture philosophical question the solar energy research community has finite resources there's only so many hours in the day how much should we be putting our effort towards you know anyone specific material system like perovskites versus you know looking for new materials that nobody's even thinking about right now should we let our guest have the last word I was going to say Brent knows the answer to this one well it is a very exciting time to be doing computational work because we can consider so many materials right so actually the cost of exploration right now has almost never been lower from a simulation so that's very exciting you know we use these terms like breaking the sort of Edisonian paradigm where we actually have to synthesize the thing and test it I mean we're trying to accelerate that thousands to million fold using simulations nevertheless if you're dealing with a long gap development life lifetime on the decades time scale I think we do need to be investing in today's technologies right now any other comments I would just say that the cost of the early stage investigations is always going to be a small fraction of the overall amount of money we're spending on research development and engineering so it is going to be important to cast a wide net at early stages we're also going to have to be really ruthless in terms of narrowing at that down because there are a lot of materials that I've seen over the years that people thought should be incredibly good for PV and they were like so excited about it and then they tried to build a cell and then it's like less than 1% efficiency I'm not saying this to pick on anybody but just to say that it's a long and difficult road to develop these materials and we need to be aware that there will be a lot of failures along the way but perovskite is definitely a very promising path but again it has to compete with some very massive technology that's already been around for a number of years so it is a challenging hill to climb but it'll be interesting to see what happens let's have a very brief summary and then we can end the session well I think these guys got it right I agree with their analysis that actually we can't spread our bets too much for the reasons we're all aware of but that we do have to have some stuff that's further along that will push towards commercial impact but we have the pipeline it's actually back to the point we've all made a few times about basic science I mean investing in basic science is really feeding the pipeline of talent like you guys feeding the pipeline of ideas and feeding the pipeline of knowledge so that we can then mature the technologies that are winning so I do think we need a little bit of a pipeline strategy okay so our time is up let's thank all the panelists again particularly thank Professor Sergeant for coming to Purdue to talk his wisdom disaster and thank you very much for attending and thank the Collier of Engineering to organize this wonderful event thank you