[00:00:19] >> Ninety nine hundred ninety nine will be OK thank you for the kind introduction and let me just make a small remark on the title of the title of maybe the dawn of organic optoelectronics because as you know optoelectronics a very important area and most of you probably working on up to electronics with conventional in organic semiconductors what I would be talking about today is an area which is still I would say in your early days. [00:01:55] There are no huge markets for some of these not materials yet but as you will see this is an emerging in. We've a great economic potential and also great opportunities to do science and. And engineering. So just a quick note everybody is talking about the weather these days and these temperatures about one hundred well you mentioned that. [00:02:22] I spent about twelve years at the University of Arizona. There in Phoenix. It was a hundred eleven last week and we had often one hundred days in a row we've temperatures of one hundred so right know these few days of over one hundred actually not so bad. Let me stop by knowledge ing the contributions of people from my group. [00:02:46] As well as mention collaborators and we touched on some of the work that has resulted from these collaborations. But there's a lot of other things that are going on that I won't be talking about today and some of the work in particular on the organic photovoltaic So we're talking about. [00:03:09] It's been done by you know William what's gathered here I'll be talking about some of the transistor Well that was done by Chung Zang and some of the lighting meeting and display results been done mainly by him here and only asked how to do. You are a graduate student. [00:03:30] So we had the chance to move into a brand new facilities last fall and so we currently located in the so-called end building which is not a color science and engineering the building which is on that biotech area and all our trees are on the faithful on the East Wing off of that building. [00:03:56] It's a nice environment because it is a building where that houses faculty from values that pop. Once and we're all working on kind of a common theme which is organic based materials for value either organic or for tonic or biological applications. So all from my talk today I would start by kind of giving you a very high altitude picture of what that area is all about and then. [00:04:30] Introduce some of the basic concepts. I'm assuming that most of you are familiar with traditional Crystal and highly pale you know leak. You know getting so many conductors and the corresponding optical and electrical properties as you would see here because we dealing with organic materials that tell me Knology and some of the concepts are different. [00:04:53] However they can be connected to existing contact concepts and so hopefully we've that. It will make things easier to be understood. And then I will touch on three examples of technological areas where these all got it based all these synthetic compounds are having a big impact and at a point where you know some of these areas have already led to some commercial applications some others are just didn't even in the process off being transferred. [00:05:31] And they progress he's made it a very high pace in this area and of course it is a very competitive very vibrant area of science and technology. So the first question is you know what are these materials group for and we're all familiar with so-called plastics which have become the commodity and which are widely used in all daily lives but so far. [00:06:00] Mainly for their mechanical properties in lot of the organic materials are you. The packaging. But I should also note you know and remind people in that audience that electronics and in particular a lot of photos he took are fee which has enabled the publication of integrated circuits was made possible because of some functional organic materials for resists are basically materials which formed into the class of compounds that we use now for other applications. [00:06:30] And so really one of the important point here. Points to feel strong is that we're dealing with organic material means carbon based chemistry. OK so all the molecules all polymers that we would be using mainly based off and then hydrogen oxygen nitrogen the few met a lot but in vast majority it's carbon and gallon chemistry is very rich as we know you can make very complex molecules in particular. [00:07:05] Biology but we will be using very simple blocks distastes The other difference from you know difference of organic materials compared to we have some of the you know again I think crystals that are grown by value of steak Meek's is that you can form films and functional materials. [00:07:29] And use Vaillant into molecular forces. And so that's an additional level of flexibility at the same time it is a challenge because it makes it more complicated to control the morphology of these films. But at the same time these organic molecules can be deposited onto any substrate because most of the time the processing in contrast to inorganic semiconductors is done it through temperature so you compatible in particular we flexible plastic substrates. [00:08:03] And so on. Days that they division that these materials are compatible with light weights and highly flexible substrates and that as a consequence you could potentially manufacture some of these devices at very low cost using room to room manufacturing processes and so just a very brief note here on the history of some of these what I refer to as industrial plastics because the concept of synthetic organic molecules goes back to the one nine hundred century. [00:08:40] But the first real industrial plastic was developed by rather skyrocket was here at Dupont. In the thirty's and it was nine. OK And shortly after the first commercial application for all these synthetic polymers wear stockings and they're using nylon fibers. And then in one thousand nine hundred seventy seven. [00:09:06] Some of these gentlemen here received the Nobel Prize in chemistry and you know two thousand made an accidental discovery and they discovered by mixing some catalyst in large amount with Setian that they could. Some of the materials which previously well known mainly as insulators they could basically turn some of these materials into these metal like highly reflecting conducting materials with connectivities comparable or even higher than copper. [00:09:38] And that is somehow referred to as the beginning of that new era where from conducting putting moves then people started to look into some conducting polymers OK but as you know it will run of the fundamental pectin metric for inorganic semiconductor or any semiconductor. Eased the charge of mobility and so if you look back in the early eighty's. [00:10:04] Some of these organic compounds had been investigated for their semi conducting properties. However the tchotchke area will be eighty's where in the ten to minus five square centimeter provided second range. OK And so during that period here. There was one big commercial success. That was based on organic materials organic some conductors and that was zero graffiti. [00:10:31] OK since even today. Most of the photocopiers that we use are based on drums where the foetal conductor in that general graphic process East fabricated from an amorphous organic some conductor. And full of zero gravity process maybe D.T.S. in that range ten to minus three to minus four. [00:10:53] And so there was no need for materials we've got higher mobility and that's a ten billion dollars business. OK And the reason these organic materials to go over are more for city council some of the other materials is because you could cook them onto a flexible substrate and there's such you could call them on a drum and then all of a sudden design process. [00:11:16] With that circular symmetry. And so over the years you can see that by playing with the different groups and improving the processing of these materials and the purification of these materials. These will be the teas have improved by orders of magnitude to a point where now they are competing sometimes exceeding the type of charge will be teased that you can had to seek on however here with the put possibility to fabricate these materials and these layers the trim temperature on to any substrate with similar properties so I'm off acidic on these kind of the benchmark material for us and we see that we are almost there. [00:12:00] So where do these organics I mean conductors play a role. Well. Well the most advanced area and where you are already find some cell phones or M P three players with full color displays fabricated from some of these organic molecules is a display area. And you can see this is not a commercial product yet but it is a prototype off color T.V. which is fabricated from organic light emitting devices and right now most of the technology is on glass from fairly low efficiency. [00:12:37] However the efficiencies in recent years have really increased significantly to a point where these same materials are now also const being considered for so that state lighting up the Haitians. And that we share with you some of the results we've got here at Georgia Tech even making fairly efficient devices and so you see why this is such an active and vibrant area. [00:13:03] These days. Another area that of course timely. And. Is the potential to use some of the same organic some of conductors full throttle take up the cations And so a small Paul sources. Now you know these sparging aeration plants large area that might be you know ten years out there but all the applications where you need to power a little while as devices where you don't need much power you don't want megawatts but you can live with the media watch so microwatts that's an area where some of these organic materials will play a role in technology in a few years and then there's a whole area here off. [00:13:45] You know what people refer to as printed electronics which is the really grail is to use some of these materials like inks in your printer and printer conductors you insulators your semiconductors and design any kind of circuits of course they will be slow. There are tradeoffs. But because of the potential. [00:14:05] To manufacture these materials using conventional printing techniques from rule to roll large area very large through Pruett to some drop in demand that type printing that that potential is of cross generating a lot of excitement and if you look at some of the market forecasts for these printed electronics technologies. [00:14:34] You know they are significant and I thought that number which came out a few years ago was way too optimistic but some of the most recent reports that are being published by some of these marketing research films. Actually even higher than that figure so there's a lot of potential here of course many many barriers to overcome before this becomes a mainstream technology. [00:15:01] So all of the work we do here is of course done collaboration with many colleagues was in the center of organic photonics and electronics and also could be possible result the infrastructure that we have here at Georgia Tech and like to point out that you know the infrastructures that we have here at M I L C absolutely essential in enabling us to do for although we've the technology and we have some other specific equipment which can accommodate some of the limitations or which is compatible with the limitations of organic materials which is namely the ability to fabricate and test some of these structures enough that most fear. [00:15:44] We've also set up a lot of. Terrific Asian stations so that we can fabricate organic materials we've high purity. So let me now switch gears and somehow review some of the fundamental processes awful Ghani molecules and probably most Not a lot of the blood. Stick materials like the plastic that was used to make that cup here is. [00:16:11] Produced from pretty mirrors where you have very long chains off goblin not guns that are connected together and usually the bonds the covalent bonds between these goblin not arms are single bones. OK. Now because of the complexity or the reach gave me strength of God you know that you can from either single bones but you can also from double bones and triple bonds and that has to do with the fact that the gal going the state covenants and it has one S. electron and three P.. [00:16:45] I mean one S. all beetle and three P. all beetles and you can form different hybrid all beetles with these different all beetles and so all the materials that we would be focusing on today which have these unique semi conducting properties conjugated molecules where you have to tell needing a single and double balance. [00:17:08] OK And the reason for the interesting properties here of these materials we have that the conjugated structure is that on each goblet not them. You have an electron even hybridize P.C. all brittle and way function all the charge density East eking out here and is perpendicular to the plane where you have these other regular single album bonds. [00:17:37] OK. And so you can form chains or you can form to dimensional molecules such as benzene molecule is one of the simplest molecule you can make three dimensional molecule such as Bucky poles and full rains or you can make these very long chains off probably mirrors and you know all of these cases you can see here you always have as you move from one cabin not on to another one. [00:18:01] You're going to have done a thing. Single and double bond see. Same here. And so on and so forth and what we're really making use off. Are these deal look allies. P.Z. all these spy electrons. OK. And because of the difficulties ation of these electrons you can have interactions and you can have chops transfer reactions taking place between these nearby molecules. [00:18:29] So we'll call it to describe these molecules all these solids because we dealing with state films. Well you can look at a single molecule here first approximation as kind of a two level atom or two level system. OK where you have two electrons here with opposite spin because of forty's exclusion principle. [00:18:55] Bonding all brittle and so these orbital easies full here and then you have an anti bonding also called by Star which is empty. Now in a solid You don't have isolated molecules these molecules are interacting and there is some overlap between these molecular all beetles and that overlap here leads to the splitting off some of these isolated energy levels and in a solid where you have a lot of these interactions these two level discrete levels here turn into bands and beautiful bands which are separated here by areas where you don't have any density of state or an optical band. [00:19:43] OK And so this is kind of the off man structure in an inorganic something Conductor where you have a violence band OK which is which is filled and you have a conduction band and you have a man gap where you don't have any states in between and if you come in with a photon. [00:20:03] Well OK. You can promote one of the electrons here from that the highest molecular orbital into the lowest and occupied molecular orbital So think about the room or level like the violence of the and then the level like a conduction band but then here is not meant in the same sense as in an organic semiconductor where you calculate the bend structure. [00:20:29] It's more you have discrete levels with some with because of interaction and disorder. And so how do you have chalk strong now from point A to Point B. in one of these films. Well charge hopping. OK or an electron transfer reaction so if you take here. This is a cop doing where you have two of the simplest molecules you can think about to bends in. [00:20:57] Molecules and they are in close proximity. And you can see that these red circles here are. Supposed to show these spy electrons which are a nice P.C. all bottles that are sticking out of the plane and because a deal. OK is ation when you bring these molecules in the air by they will be let up between these electron densities and that coupling between these molecules will allow an electron to hop from one molecule to another one and you can think as electron transfer all the whole transport in these organic semiconductors as a process where you have multiple hopping from one molecule to another one through either the level. [00:21:43] If you're dealing we've holes all the human level. If you're dealing with electrons and of course you know the bomb eater that is of interest here is trying to use the mobility and we like to optimize this. So this is just another cup tune that repeats some of these concepts where you see here in the background these kind of the tell you know the. [00:22:04] Lattice the same light as you would have in a crystal. But here because you have a solid of organic molecules which are bound through week one day about its interactions and because you don't have very high pay you decide. You have some positional disorder. So the average distance between molecules is changing and furthermore the energy levels of these different molecules are not lined up perfectly because for each molecule the environment is slightly different and so they can be some so-called energetical disorder. [00:22:39] And so as a result as a result the mobility here is actually a fairly complex function of Applied electric field because the electric field. Can we assume most fall trying to get the laser pointer to work. I don't know if you batteries. Yeah but only we do work we owe. [00:23:16] But the laser pointer should be separate. OK. Will is struggling we've power we need rechargeable batteries and connected with possible so ourselves. So anyway. Thank you. As I was saying the mobility as a result is a function is a complex function of the electric field. And the electric field as a drift also helps in bringing carriers across a film and then of course as a function of temperature and here. [00:23:52] If you view transport this a multiple hopping process with some trapping in between hops. If you increase the temperature you're going to minimize the trapping time of these carriers. And you would be able to have higher mobility so this is something at least we have some models and then as a result of course the magnitude of the challenge of mobility is going to depend a lot on them not follow G. of these films and the order you have like in organic crystals The higher the mobility the number office materials the mobility typically is going to be below ten to minus three smaller values and then you can also design materials that selfish Sun building to liquid crystals where you can have the processing of amorphous materials with the order of crystals. [00:24:47] This is kind of a energy level diagram which repeats some of the basic concepts I've already discussed but which are very important to understand how the devices that we be talking about next operate. And so here I've represented by layer device sandwiched between two metal electrodes or two conductors and the reference here is the vacuum level and this is an energy level diagram and so you can see this here is the work function of one of the metal which is typically used as an anodyne if we dealing with a light emitting device and here we have a little function metal. [00:25:31] So these are the levels of the metals and then we have two different materials so that would be two different molecules don't like molecule which has and I need zation potential here which corresponds to the energy of the home or level with respect to the reference all the vacuum. [00:25:53] And the electron affinity of that accept type layer here and you can see that you know typically for whole transport you want little I knew zation potential for. Electron transport you want fairly large electron affinity because you have to inject charges from metals and you don't want you limited by you know the smallest rock function you can get for from metals. [00:26:21] OK So this is typically the cross-section of the light emitting device all a photo will take cell where now if you bias that structure. In a foreign or LED or an organic light emitting device. You're going to inject holes here into the home or level of homo band or one of the layers. [00:26:43] On the other side you're going to inject electrons into the limb or level of that other material. OK Here you see it's much more difficult to inject electrons into the human level of that because you have a huge barrier for injection. Likewise it would be very difficult to inject holes into that layer because you have a huge barrier no difference here between the homeowner level and the family level of the cattle. [00:27:07] OK So this is where you pick your materials or you design your organics I mean conduct is such that these essential energy levels are where you want them to be now in a photo voltaic cell it's the opposite process where you absorb a photon by any of these two materials and then you have charge of dissociation and you collect the electrons which are transported here in the human level of that layer and the whole which is transported in the home level of that other two. [00:27:40] So let me switch now to examples of different devices that we fabricated from these organic semiconductors and the first one relates to displays and state. Lighting and describes the operation of these so-called LEDs which stands for Gannett light emitting devices and you can see that's a typical cross-section where we have these tools. [00:28:04] There's that. I just mentioned earlier one being kind of a whole transport layer the other layer from a different molecule being in the electron transport layer and then different conductors for electrodes and for the lead because you want light to come out or for photovoltaic cell where you want light to get absorbed by the material. [00:28:25] We often use a transparent conducting oxide and look side is kind of a fairly standard D.C.U. right now. And so if you bias the structure you're going to inject holes into these group molecules here are you going to inject electrons into these green molecules when the whole and the electron get together they can form an excited state and then the molecule will relax to the ground state and emit light. [00:28:55] OK And so these different processes are far shown here on that chart where on one side you can inject holes on the other side you can they inject electrons to Mathilde's because these are organic semiconductors will be transported in these different layers and then from resultant recombination they will meet their way from an excited state. [00:29:16] And then it will be emitted and then finally there is a last step there where the light at that Shane aerated here was in the device has to make it out of the package like any other light emitting device and so if you look at the overall efficiency here of that device it's limited by film and factors one is the efficiency at which all the holes and electrons that are injected into the device lead to an excited state that's fairly high that can be close to one hundred percent. [00:29:45] Then you have an important limiting factor here which has to do with the spin of these chargers that you inject And so when you inject it all on an electron that particle has a spin either up or down and so when you have two particles. You can form either. [00:30:05] It's all triplets States and so they are four different combinations three of them are triplets and one of them is single it. OK And then for symmetry reason. If you have a few arrests and molecule you can only have emission and fluorescence from a single state. And so you can see that if you have molecules that fluoresce you get a bit limited here to about twenty five percent of all the Excited States which can only emit because the triplet States because of symmetry reasons cannot emit and so you lose a lot of the light and then of course also there's also another limiting factor which is the fluorescents efficiency. [00:30:44] How many of these Excited States fluoresce how many recombined known radiatively OK and still depending on the material platform. You're going to be limited by the efficiency. And so a lot of that work was initiated in the early eighties by a chain gang at Kodak. And at the time he reported an organic light emitting give ICE based on that green a meter aluminum quote in the typical performance of these devices are shown here. [00:31:16] This is an electrical current as a function of applied voltage you see this kind of a turn on voltage here of the order of two to three volts and then by the time you are about to seek seven volts. You have a brother thousand condé Nast discriminator of light emission I remind you your laptop or or your T.V. screen about five six hundred conduit us to square meter. [00:31:41] So these are brightnesses that are the same level or even higher. But you notice that the external quantum efficiency of these devices was only of the order of one percent. So it was significant at the time but limited and then through the ninety's the efficiencies improved to a level about close to five percent. [00:32:00] OK And again the limiting factor was that when. Stricture than that you could form on the twenty five percent of cigarettes and you were throwing away seventy five percent of triplets. Because you were dealing with fluorescent molecules. And then in the late ninety's people realized that you know they are molecules out there so-called phosphorescent molecules where by coupling and organic League and the heavy elements such as platinum here or you can break the symmetry. [00:32:35] And you can have light emission from the triplet states of these phosphorus and molecules. And if you don't get these phosphorus of molecules into a fluorescent matrix and if you take advantage of to make an ism of energy transfer or the one being a long range first of type energy transfer air between the single it states and the other one being a short range. [00:33:02] Dexter type energy transfer between triplet states you can actually harvest all dissing that and triplet excited states that are formed in new material and end up with only that excited force fluorescent triplet state which can then lead to light emission. So this is a way of harvesting all of the Excited States or another way of saying things is that you can now have potentially an internal efficiency or for one hundred percent. [00:33:35] And so this is not a strategy in this area and still people throughout the world are walking on the emissions organic electro phosphorescent materials and just want to here to show you some of the work that we doing here at Georgia Tech where these are data that we obtained a few months ago. [00:33:57] We are now at an applied field of an applied voltage of the order of seven volts. If you. Pick your transport material property. You can get you know light outputs again which are close to a thousand condé Nast per square meter and we've extended contemn efficiencies which are now getting close to twenty percent. [00:34:18] OK. The latest device we fabricated is an efficiency of twenty one percent. OK. Now if you consider that because of total internal reflection in the current then film structure. You all being on the about twenty five percent of the light that is actually produced in your device you can see that the overall internal If you should see for the whole process off it actually mean essence is you know approximately four times higher than these external quantum efficiency so you know we get eighty eighty five percent range and there's always even been a report recently from Japan where people we reported twenty nine percent. [00:35:03] Now we're getting close to hundred percent. Now the game is shifting from optimizing doing to only fission C to actually finding ways and means to Odd Couple more light and this is where putting on the ng and microstructure ration of that substrate is going to be very critical and we're working on this. [00:35:22] We not just making single light emitting devices we're also learning how to putter around and how to make food displays from these materials where we use value as processing techniques to run these what you can fabricate some pillars here where when you deposit on that structure because of shadow masking effects you can define pixels and you can make full displays and here is just an example of a seven by eleven video display that my graduate student which I'm baking came deadlocked and we've some blue meters that were developed at the University of Washington and combined with some materials here. [00:36:04] At Georgia Tech and so you can see you can easily scale this up and make displays of larger size but. This is just a kind of an even stray shouldn't shows also the integration where we don't just throw on materials and discrete components but also moving into the subsystem level. [00:36:26] So let me switch now to a second example where Danny semiconductors are making a lot of progress and. Gaining a lot of attention and that's the aerial photo it takes. So today of course most of the photo will take technology and related systems are based on Crystal and silicon Crystal and silicon can be produced from different techniques in different forms. [00:37:01] They also some so-called second generation thin film approaches based on them off a CD Kong and some copper in your silly neither or copper in your cell and I as well as carbon terrorized you have some very high and very expensive photovoltaic devices where you can use three five. [00:37:25] Semiconductors that are grown with conventional and we see video M B type techniques and organics are kind of new comers and again this is something that is now receiving a lot of attention and the most efficient devices so far that have been demonstrated are still little but you know they are all of the order of six and a half percent. [00:37:49] And so at a level where. It's not negligible. OK. And so we're not really competing with silicone here in terms of efficiency but these are materials which again because the way they're processed they could lead to for. It will take cells which cost much less than the conventional cells and modules based on. [00:38:12] Dicing and assembling Crystal and sequin wafers. And so why do we need to optimize to transition that technology of course the spa conversion efficiency and so what we need to do is take the last Bactrim which is shown here. This is actually the spectral photon flux density as a function of wavelengths for standardized even nations so one sun typically hundred me what the square centimeter and you can see here the black kind of the current you can expect if you harvest all the thought on starting. [00:38:51] The blue part of the spectrum and growing into the infrared and of course somewhere here. There is an optimum condition because photovoltaic cells are part devices and what you want to do is really optimize the problem version if you can see which is optimizing the open circuit voltage as well as the short circuit current. [00:39:11] Now in sequence cells. The basic structure is a P.N. junction. OK. And when you have absorbed a photon in silicone you pretty much creating an electron hole pair and those get separated in the junction and then they get collected by the electrodes you don't get it. Materials the situation is very different and this is why the cells are sometimes referred to as exit or leaks or ourselves. [00:39:39] And the reason is because the dielectric constant of organic materials is much smaller than C. code. OK see guns around twelve thirteen materials it's closer to three to four. And so as you know when you absorb a photon. And you create an electron the repair you have to put it even in the charge and these two particles under contract. [00:40:05] OK. And so they can form a bond state which is called an exit on which is pretty much like a hydrogen atom. OK where you said the charge in the negative charge correlated the bond together. Now if the binding energy of that is smaller than K. T. at room temperature the exit on breaks up into an electron hole pair which is the case in Seek on because you know Katie at room temperature being of the order of twenty six mv the binding energy of an X. You don't mean you can use more than that but you know the guy next the binding energy is a few hundred medievals half of all. [00:40:44] Ok much larger than K.T. a true temperature. So when you absorb a photon you don't have current right away what you have is an accident and you need to find a way to break up that exit on into electron who appears and so that is done at interface between two molecules with different electrical properties and it's kind of shown on that got to one here where now remember the energy level diagram that I described earlier where you have the one you more level of one material and don't want to do more level of another material. [00:41:23] If you come in with a photon you have Zob that photon you create the whole electron here because of the interaction which is not screened very well because of the low dielectric constant you going to create that exit on. But any exit on that makes it to that interface here because you have a driving force and a sufficiently large difference in energy levels here between the lunar levels there would be a charge transfer reaction then the exit the exit on the break up. [00:41:52] No you have created all here an electron which are no longer correlated right at Coolum interaction and now you can have currents and now you can collect the electrons here you can elect collect. Here. That's how organic sauce cells work. No of course. One of the limiting factor is hard far. [00:42:14] Can these exit on Google and can they reach the interface where they break up and contribute to the current or will they recombine before. OK. And so if you're limited by that so-called exit only good fusion length. You have to make the films not more thicker than that extent if you can then I ever. [00:42:36] If you make the film too thin. It doesn't absorb light anymore. OK so the whole game has been trying to understand what limits the extended diffusion length and developing materials we've increased extending diffusion lengths such that you can have good light harvesting and better efficiencies. Now if you're limited by the extended diffusion length there's another little trick you can play which is rather than making by later structures like this you can mix the compounds together. [00:43:04] And as a result you're going to have you're going to fall my lot of these hits will junctions here or in the bulk of the material. And so you have interpenetrating networks here or face separated domains and you can have correlation channels for holes and electrons and this is a an approach which is we fail to as all control junctions because you creating hit your junctions everywhere in the volume of your material and so anywhere you absorb a charge you always have or you absorb a photon story you will always have an interface and thereby where the exits on can disassociate. [00:43:41] So with that introduction Let me now switch to describing some of the work we have done here at Georgia Tech where we combine Penta seen. Which is a well known got a P. type semiconductor. And which actually forms pretty crystal in films we've very high mobility and which turns out is a material which has a very large extent you get fusion length. [00:44:03] So this was a. Or donor or not your whole transport layer and we combine that with fullerenes which are well known acceptors or electron transport layers and we also used another layer here to prevent extends from the associated at that interface here. And so with that basic structure here. [00:44:23] We've been able to fabricate devices we talk on a version a fish and seas of the order of three percent. You can see an open circuit voltage here of the order of point four and currents which are you know in the range of fifteen million square centimeters. And these devices have very nice characteristics which you can model with some conventional equivalent circuit models which you brought from silicon and here on the right hand side you can see the external Cottam efficiency which is defined as you know the fusion C at which you're generating electrons all pairs that contribute to the photo current per incident fought on and you can see that in the area here where Panther seen absolves you can get values that are as high as close to seventy percent. [00:45:11] We're not doing a very good job here yet harvesting some of the photons in the visible but you can see there is a lot of room for improvement. And this is right if you can see these in these particular devices only in the range of three percent right now but there is great potential to a further improve these efficiency. [00:45:31] I am not going to talk much about the modeling of the extent of diffusion but. What I would like to mention also is that of course like any of these organic material or any new material technology. It's very important to make sure that you can process these materials into devices that you can use in the air in the environment and organic compounds are known to be fairly sensitive to oxygen and moisture. [00:45:56] So whenever you have oxygen and light you can have photo exceed any of reactions which limits their lifetime. But. We've. Recently applied to make layer the position to encapsulate some of these organic solar cells and you can see here these are efficiency measurements for these packaged devices and this is packaging that is done at hundred fifty degree C. so it is compatible with plastic substrates and you can see we have shelf life times and we've done our measurement measurements recently we have beyond ten thousand years now which is over a year of shelf life time with that packaging technology which is very promising and we also done some tests under continuous in the nation and so far after one hundred hours of continuous the nation to dig radiation is less than ten percent of the initial value which is much better than. [00:46:51] Now another big advantage of these organic materials is you can easily monolithically integrate them to make modules when you make a module from Silicone you are limited by the way for size of your silicone and you have to assemble these cells and wafers into complex structures here. We've demonstrated and this time we switched material platform we use some rather than the small molecules and these have a little bit fairly higher efficiency of the order to four to six percent of the pending on the spectrum that you use and you can see we've displayed in most cells the external quantum efficiency now is in the range of seventy five to eighty percent and that translates into four percent proc inversion efficiency. [00:47:35] If you integrate these values we've standardized and one point five global values and so just by putting on the NG The conducting oxide and the positing a continuous layer here by spin coating and by evaporating the top contacts through Soma shadow masks. We've been able to form demonstrate molecules and what you expect if you connect these modules in series of crosses that you open circuit voltage scales with the number. [00:48:04] For devices that you connect and you can see we've made modules We've or prating voltages close to two volts which is enough now to recharge a lot of secondary batteries. Let me how much time is left to minutes all. OK. Sure. So I'm going to really speed through the last part of my talk here which is on organic thin film transistors as I mentioned earlier our benchmark is I'm off to seek on the big advantage here that you could process these materials onto any substrates at room temperature. [00:48:39] But the biggest advantage is that as you know we've got more physique and you can make good type field effect transistors but P. type are terrible. So you can't really make CMOS design with. Weave them off a City Con The right here. We've all got it but tools you can make potentially see more so if you can have the Road Transport an electron transport materials and. [00:49:04] In recent years a lot of if lots have been devoted to P. type or Ph channel thin film transistors and there wasn't very good and channel transistor and we tried to solve that problem and we picked C sixty the same material that we use in our photovoltaic cells because we've learned a great deal how to purify that material and how to process it properly and the first. [00:49:30] Nice results we got a few years ago. We've see sixty You can see this is the transfer characteristic of a transistor we've got bottom electrodes fabricated from C sixty eight. These are great close to a point to run square centimeter provide a second but you see the big problem was that the threshold voltage of these transistors was terrible ordeal rule for evolves and so by optimizing the device geometry and playing a lot with the dielectric that is used for the gate. [00:50:03] We recently. Able to fabricate transistors with you know almost takes work type transfer characteristics and we threshold voltages close to zero excellence threshold slopes and carry them abilities are from three to five depending on the channel with. Length ratio and in addition we've also identified some hydroxyl free dielectrics. [00:50:30] Which provide devices with excellent stability. This is just repeated I.V. characteristics measured over one hundred cycles and there are no signs of the grid ation So you know that combines high mobility and groups that beauty and so in conclusion. I hope I've shared some of our excitement in this field review and convinced you that you know this is a technology. [00:50:59] It's kind of we're seeing the emerging people of the iceberg there's a lot of potential it's not the mainstream technology yet but if you look at the slope at which the progress is a current he made in these areas is really exciting and I think it holds a lot holds great promise. [00:51:20] Now I did not touch on some of the telecommunication or some other optical properties but I should just mention that that's another area that's very exciting and recently materials have been developed which have electron fissions which are ten times those of bait in terms of the light sources differently. [00:51:41] Many applications in these plays and in the near term. I also believe that these technologies will lead to some neat so that state lighting devices with if you can see these higher than one hundred lumens per watt and portable power we have the organic photovoltaics is something that's going to happen soon as well we probably initially proc on version if you can see is of the order of five percent but the material. [00:52:04] On the technology has a potential to grow all the way to about fifteen percent. Now I want to review it. So I don't want to mislead you and make you believe that you know this is a technology where we've sold all the problems they are still many challenges. [00:52:21] It's going to take a lot of a fault but suddenly I think that the next decade or so is likely to see a lot of new applications and that field we continue to grow and become a very active area of research. So thank you very much for your attention you give us a gift when you're willing to speak during summer. [00:52:57] OK thank you very much. We have thank you and I appreciate you coming. Maybe you could have used that as a pointer actually the bottleneck in what sense right now the limiting factor has been the high cost of tooling because. There's a lot of infrastructure a lot of technology that has been developed for the processing of liquid crystal based displays. [00:54:12] And the lead. Manufacturing is still pretty expensive compared to liquid crystals. But you know as the field is growing these costs come down and they will become a very competitive area. So you know I think the challenges will be to demonstrate that you can process these materials at a cost that is significantly lower than some of the other technologies. [00:54:44] And so you know right now a lot of the early commercial products are based on fluorescent small molecules which are processed from the vapor phase but they also if it's where people have made prototypes where they use inkjet printing. OK And they are you no longer limited by the size you can grow to a larger area. [00:55:05] So it's it's really I think a problem of the whole field maturing at all levels from the generation of better materials with better properties to people getting to know these materials and then working on integrating these new materials into the our designs but I think the challenge right now this is often perceived also as chemistry. [00:55:38] OK And you can take any textbook in electrical engineering or any semiconductor textbook and there's nothing on organic materials and so a lot of people from I would say traditional engineering background. They're not aware of these new materials becoming available but this is going to change and that's when when these. [00:56:04] Materials will become mainstream. That's where things will start to take off and grow exponentially. I can say also that you know there are few companies out there who are working on these technologies and they can't find enough students or Ph D.'s who actually you know do work in this area. [00:56:27] So most of the students who graduate you know are groups they have several job offers lined up you know the hard part is to choose one of them because they so much activity and this will only grow more as in future years or yeah no no definitely this is not exclusive. [00:57:20] OK You can also right now you can print some other materials in particular something that's becoming very attractive is to make inorganic semiconductor or Excite nanoparticles and then quote them we've some league and such that you can sort of belies them and put them in solution and then print these none of composites and sinter them at very mild temperatures which are compatible with plastic substrates and get the desired dielectric or conducting awesomely conducting properties. [00:57:54] So a lot of the inks that are being used are not exclusively carbon based you can combine them with you know get it based nano composites further. Whenever you need speed. Let's say you. You know you probably Kate and active are if I do or wireless sensor something like that you can't fabricate and design the high speed electronics with these government based materials because they are too slow but nothing prevents you from you know taking some CMOS I.C.'s and integrate them with the printed platform. [00:58:28] So it's it's not a competition to CMOS it is really complimentary. And I think it's it's by combining the different technologies that where the sweet spots are now that's the beauty of it. I think that the integration The Hitcher genius integration here is really very easy because all of processing steps are done at room temperature. [00:59:13] And so you know the trend is to develop some inline tools where you just go from one chamber to another one on the you can do that at the wafer scale where you start with a piece of glass always a piece of plastic on the carrier and you put it in the last chambre where you do a first method is ation. [00:59:32] You move it to a second chambre where you do some patterning you move it to a third one where you deposit so many duties and so on and so forth and you can develop the backplane the transistors needed to control the pixels for display and deposit the organic materials and package everything in in-line tooling so that that is really the vision right now how things are evolving. [01:00:09] The yeah it is it is one but it's not one that. And so mountable OK And I think the example is what I've shown we've where using a very simple process and putting just down a pretty thin two hundred ninety meter think layer. You know you could get shelf life times that exceed a year. [01:00:42] OK. And I should mention since Nam Sue is in the audience that we currently having a collaboration with Professor Sam Graham from the school of mechanical engineering and he's developing some barrier coatings for all printed electronics and they've already achieved world of a put transmission rates in the range of ten to minus five. [01:01:07] OK which gives you over ten thousand hours of operation if needed. You know most of the barrier coatings that are used for instance in food packaging and so on that these transmission rates are you know deal with ten or run that these are some of the best very according to their down now two to ten A minus five. [01:01:27] That's plenty that's good enough for P.V. So the whole area now is ease of course everything is important but I think they are packaging technologies that are starting to show up. Which are compatible with these technologies or these materials like. The temperature is a problem if you go beyond the composition temperature of these organic dyes and so you know typically. [01:02:05] You can make pretty robust dies with the composition temperatures of the order of three hundred degree centigrade. But one hundred degree centigrade hundred fifty degrees centigrade is not a problem not the properties are changing. But you know for instance the mobility here when you increase the temperature you have higher mobility. [01:02:30] So your devices on parade better at higher temperature. Than at low temperature which is kind of reversed with the traditional conventional inorganic semiconductor where the movie goes down as you increase the temperature but of course all these things will have to be looked at but at this point there is no reason to be concerned about operational temperature within the range for instance if you take a display based on liquid crystals in the air the restrictions in terms of temperature from peroration is much more stringent because as you know you know you have these face transition temperatures so you can go beyond all below a given temperature. [01:03:10] This is what you package those we lose our little heaters such that if you keep your L.C.D. display in your car during the winter if the temperature falls below a given temperature you have a little heater that kicks in and keeps the package at the desired temperature so I think that temperature wise these materials probably more robust than than a lot of the existing display technologies and yes yes the answer is absolutely yes. [01:03:59] And so people have made them normal to pull junction cells. OK So if you're limited by the harvesting you can make multiple junctions that's that's one way you can also harvest different parts of your spectrum by having multiple junction devices and so the most efficient device organic device. [01:04:22] We've brought up to date which is a report that appeared in Science a few weeks ago. E's one of these top themselves where people combined different materials we have different absorption spectrum. Yeah I mean you know if everything goes well I think that in terms of dollars per watt you could meet the one dollar per what Dogget However I think it's premature to talk about a large area applications because a lot of the test structures that have been reported on you know are small area devices and there are tremendous challenges to scale things up. [01:05:14] And secondly I think that in terms of lifetime of these organic materials as much as I can see them perform well you know while a sensor that's deployed and has to operate there in the field for about two or three years at this point I wouldn't put organics all ourselves on my roof because you know I don't want. [01:05:36] I don't think they're going to last for twenty years like Siddique and so they are many challenges until organic photovoltaic technologies really make significant contributions to power generation. So the model and the field of use or the type of applications. I think very different than some of the mainstream would take technologies. [01:06:06] Well thanks for the I'll talk you.