Archives for posts with tag: light-trapping

I recently had the opportunity (and pleasure!) of attending the 39th Photovoltaics Specialists Conference (PVSC) in Tampa, Florida. The conference, which is put on by the Institute of Electrical and Electronics Engineers (IEEE), is an annual meeting of scientists and engineers who work in the field of solar energy. PVSC attracts people from all over the world to come and share their research on some of the cutting-edge topics in the field. In this entry I will be providing some highlights of the trip, especially topics that were of interest to me.

I once again had the honour of hosting (alongside other HQP) the Photovoltaic Innovation Network (PVIN) booth. As I have mentioned in previous blog entries, the booth is where we get to represent Canada’s research in photovoltaics. A lot of companies and Universities outside of Canada do not know exactly what we do up in Canada in regards to photovoltaic research, so the booth gives us an opportunity to educate them and get them interested in our work. There are always interesting discussions to be had at the booth with researchers from all over the world!

The conference itself had a plethora of talks which covered almost every aspect of photovoltaic research. It really is amazing just how many different technologies there are for capturing light from the sun and turning it into electricity; so many that it can make one’s head spin! There were discussions on existing technology that has been around since the dawn of photovoltaics such as crystalline silicon, as well as proposals and theories for ideas that have not yet come to fruition, such as hot carrier solar cells. Two talks in particular stood out to me because of their relevance to my own research (light trapping in ultra-thin crystalline silicon). One talk, given by Nicholas Hylton from the Imperial College of London, was on using aluminum nanoparticles (microscopic spheres that are only 100 nm in diameter) for light trapping in solar cells. This type of light trapping is known as plasmonic light trapping, and a lot of research has been devoted to the field in recent years. The novelty of their approach was to use aluminum instead of the more commonly used silver and gold. The issue with using silver and gold is that although they are useful for trapping light towards the red end of the solar spectrum, they are detrimental at the blue end since they soak up a lot of the light there. Aluminum does not have this issue, and the researchers were able to demonstrate an enhancement in light absorption across the whole spectrum!

Another talk that interested me was given by Joao Serra from Universidade de Lisboa in Portugal. His talk, titled “Comparative Study of Stress Inducing Layers to Produce Kerfless Thin Wafers by the Slim-Cut Technique”, focused on the fabrication of ultra-thin (thinner than 100 micrometers) silicon wafers from thicker wafers. Using ultra-thin wafers for silicon solar cells has become attractive in recent years because of the potential to cut costs by using less silicon. Serra’s talk discussed a method for making such wafers. The process involves laying down a layer of epoxy on top of a thick wafer, then heating and cooling opposite sides of the wafer. During the heating/cooling process, a thin layer (he discussed 60 micrometer thick layers in his talk) peels away from the wafer. The advantage to this process is that thin silicon wafers can be fabricated without losing any silicon in the process. Standard wafers are usually made by sawing from a large silicon ingot; the sawing process naturally destroys useful silicon in the process.

I would have to the say my favourite technical aspect of the trip was a discussion that Martin Gerber and I had with Keith Emery, the winner of this year’s William R. Cherry Award. The award is given to “an individual engineer or scientist who devoted a part of their professional life to the advancement of the science and technology of photovoltaic energy conversion”. Keith gave me a very useful suggestion for an undergraduate lab we run here at McMaster University. The lab allows undergrads to fabricate a PERL cell, the solar cell that holds the world record efficiency for single junction silicon cells. Being a record breaking cell, it is naturally very complicated to make and students have had very little success in achieving reasonable performance from them. We shared this with Keith and he suggested that a PERL cell is far too ambitious for an undergraduate lab. He suggested instead that we make far simpler cells. Although it may appear to be a simple suggestion, it really got my thinking about how we can make the lab a better learning experience for students. I will now be working on redesigning this lab around the concept of a simpler solar cell, and owe my inspiration to Keith!

The conference was by far not the only fun part of the trip. I mean, it is summer time and we were in Florida, you can’t really get much better than that! When we weren’t attending the conference we were at the pool, wandering about Tampa, or dining at the many restaurants they had down there. On one day we went down to the beach in the neighbouring city of Clearwater. I’ve never swam in the ocean before, and I don’t think I’ve ever swam in a body of water that was that warm! Overall the trip to Florida was great, and sometimes it felt more like we were on vacation and not on a business trip! I would like to thank Jennifer Briand for organizing this excursion for us, and for all the HQP who attended for the great company and discussions we had.

Kevin's picture

-Kevin Boyd

Ph.D Candidate, Year 1

Department of Engineering Physics

McMaster University.

Several presentations at the European Photovoltaic Conference 2012 in Frankfurt, Germany, including those of Prof. Harry Atwater, illustrate recent breakthroughs in the area of high-efficiency thin film solar cells. One of the most interesting developments is that researchers are beginning to consider materials which have not been used conventionally as a thin film.

Absorber materials of a high efficiency solar cell typically comprise a significant fraction (~50%) of the total cell cost. One simple way to reduce the cell cost is to use less material. Processing solar cells with thin layers can present handling challenges for some of the materials – breakage being one of the primary issues. Nevertheless, thin materials that are flexible can enable versatility in production, such as roll-to-roll processing, and hence can significantly reduce the processing cost.

Alta Device[1] fabricates solar cells using a few micron thick gallium arsenide absorber layer. However, gallium arsenide is extremely expensive to use in large area solar cells, and thin films of this material tend to be fragile and difficult to fabricate. This is where Alta enters with its innovation – being able to make cheap solar modules that are practical for most applications using this material. Inventions by two leading academic researchers in photonic materials, Eli Yablonovitch and Harry Atwater, have been integrated to achieve this goal. Eli Yablonovitch developed and patented a technique for creating ultrathin films of gallium arsenide in the 1980s while working at Bell Communications Research. On the other hand, Harry Atwater worked on microstructures and nanostructures to improve the material’s ability to trap light and convert it into electricity. Amalgamation of these two ideas have resulted in efficiency increases at a more reasonable cost while using this material.

Alta’s cells have converted 28.3 percent of sunlight into electricity, which is the highest single junction one sun conversion efficiency record – in contrast, the highest efficiency for a silicon solar cell is 25 percent and commonly used thin-film solar materials don’t exceed 20 percent. Yablonovitch suggests that Alta in due course has the potential of breaking the 30 percent efficiency mark and nearing the theoretical limit of 33.4 percent for cells of this type.

Chow1

 Flexible power: Alta’s solar cells can be made into bendable sheets. In this sample, a series of solar cells are encapsulated in a roofing material. Credit: Gabriela Hasbun

Unlike gallium arsenide, silicon is a relatively inexpensive material. Interestingly silicon, which is the second most abundant element in the Earth’s crust ( ~28% by mass) after oxygen[2] , is also the most commonly used material in the PV industry (85%, multi-crystalline and mono-crystalline silicon combined) – a function of its economics and established processing industry. Nonetheless, efforts are on-going to further reduce cell price of silicon. Recently companies such as Silicon Genesis, Twin Creeks and AstroWatt have developed processes to make ultra-thin silicon wafers. Silicon Genesis and Twin Creeks uses Proton Induced Exfoliation (PIE)[3] method to isolate ultra-thin (20 micron thin) silicon wafers. In PIE, high-energy protons (or hydrogen ions) are embedded into “donor” wafers, such as thick wafers of silicon, germanium or other single-crystal materials. The ions form a uniform layer beneath the surface of the donor, as shown in the figure below. The depth of the formed layer depends on the energy of the incoming ions. The physical attributes of hydrogen permit the ions to penetrate the surface of the donor wafer without changing its inherent properties and characteristics.

Chow2

When heated, the ions then lift or exfoliate a uniform ultra-thin layer, called a lamina, from the donor wafer. The lamina becomes a production wafer and can be processed into thin solar cells or semiconductor devices. To use an analogy, the ions act like a scalpel and carve away thin, identical and functional wafers from the donor. A single donor wafer can be reused repeatedly to create multiple laminae.  These ultra-thin wafers contain only a fraction of the material currently used in a standard wafer for solar cells, LEDs or other devices. Twin Creeks reported a maximum cell efficiency of 11% using their 20 micon thin wafers.

Astrowatt[4] on the other hand uses Semiconductor on Metal (SOM®) kerf-less exfoliation process. A metal layer is deposited on a silicon wafer and then the wafer is subjected to a series of thermal cycles, resulting in residual stresses that exfoliate a thin layer of silicon. Astrowatt recently reported a 15% efficient solar cell using their SOM method.

It is worth noting that there are other solar cell devices that use inherently thin film structures. Examples include copper indium gallium selenide (CIGS) and amorphous silicon (a-Si) solar cells, where maximum cell efficiencies of 19.6% and 10.1% have been reported for CIGS and a-Si solar cells, respectively [5].

Chow3Zahidur R Chowdhury

Electrical and Computer Engineering, University of Toronto.

PhD Candidate (5th Year)

References:

[1] http://www.technologyreview.com/featured-story/426972/alta-devices-finding-a-solar-solution/

[2] Nave, R. Abundances of the Elements in the Earth’s Crust, Georgia State University

[3] Twin Creeks (http://www.twincreekstechnologies.com/)

[4] Jawarani et al., ‘Integration and Reliability of Thin Silicon Solar Cells and Modules Fabricated using SOM® Technology’, EU PVSEC 2012, Frankfurt, Germany.

[5] Solar cell efficiency tables (version 40) http://onlinelibrary.wiley.com/doi/10.1002/pip.2267/abstract

[6] Alta Devices (www.altadevices.com)

[7] AstroWatt (http://www.astrowatt.com)

The NSERC Photovoltaic Innovation Network provided me with funding to present my research at the AVS 59th International Symposium from October 29 through November 2, 2012 in Tampa, Florida. AVS is a multidisciplinary society that connects researchers and industry focusing on vacuum science and applications. The conference facilitated sessions ranging from advanced surface science to applications of nanostructures in photovoltaic devices to new microscopy techniques. I found the conference to be extremely beneficial to my development as a researcher, and I would like to thank the NSERC Photovoltaic Innovation Network for providing me with a great opportunity.

My research involves the use of glancing angle deposition (GLAD) to improve the morphological control and crystal structure of branched nanowires, or nanotrees, grown through a vapour liquid solid (VLS) mechanism. I gave my first oral presentation at this conference, entitled, “Engineered Indium Tin Oxide (ITO) Nanowhiskers via Vapour Liquid Solid Glancing Angle Deposition (VLS-GLAD).” I presented in the GLAD section, which allowed me to present my research to experts in very closely related fields. The talk detailed the recent development of VLS-GLAD as a new technique to grow nanotrees. In addition, I presented results regarding the performance of electrodes composed of three-dimensional ITO nanotree architectures for application in organic photovoltaic devices (OPVs). ITO is a transparent conductive oxide commonly used as an electrode in OPVs. Nanostructured ITO electrodes have the potential to improve performance in OPVs by reducing charge extraction distances and increasing light absorption. The work I presented is a significant step towards controllable fabrication of such three-dimensional electrodes.

The above figure is a schematic of the VLS-GLAD mechanism.
During VLS-GLAD, the vapour flux is incident at oblique angles of deposition (alpha), which causes flux shadowing. Enhanced control over the number density and height dependent morphology of the structures is enabled using this technique.

The above figure shows indium tin oxide nanotree structures grown at various deposition rates using VLS-GLAD. The deposition rate was found to significantly effect the diameter and branching of the structures

I attended a wide variety of talks that were relevant to my research, as well as the NSERC Photovoltaic Innovation Network. Sections focussing on conductivity in nanowires and nanostructures were highly valuable in improving my understanding over complex transport in low dimensional structures. Talks focussing on the passivation of nanowire surfaces and new electrical characterization techniques will be extremely valuable in optimizing the conductivity of nanotree electrodes in my research. In addition, Harry Atwater gave an excellent talk entitled, “Photonic Materials for Solar Energy Conversion at the Thermodynamic Limit” which detailed the road forward for solar innovation. He spoke of the importance of the development of new solar technologies such as: light trapping, photon recycling, emission angle restriction and improved carrier thermalization. He stated that high efficiency versus low cost is a false dichotomy in current solar research and that the real goal is high efficiency AND low cost for widespread adoption of solar technology. Improved photon management to reduce entropic losses was laid out as an important step toward reaching optimal efficiency. Materials and device design have been studied thoroughly. However, Dr. Atwater suggests that more focus on photon management in devices through light trapping and spectrum splitting may lead to energy conversion at the thermodynamic limit.

The AVS 59th Symposium was beneficial to me as a new researcher, and my attendance was made possible by the NSERC Photovoltaic Innovation Network.

-Allan Beaudry (2nd year PhD student in Electrical & Computer Engineering, University of Alberta)

 

Allan was the winner of the second place and public choice awards for best research poster at the Next Generation Solar – Photovoltaics Canada – National Scientific Conference held May 14 and 15 in Montreal, Quebec.  His poster was on “Vapour Liquid Solid Glancing Angle Deposition of Indium tin Oxide Nanowhiskers”.  The awards take the form of funding for registration and travel to present a talk or poster at a prominent American or international scientific conference of the HQP’s choice.  Allan elected to present at the AVS 59th International Symposium.

Figures from:

Beaudry, A. L.; Tucker, R. T.; LaForge, J. M.; Taschuk, M. T.; Brett, M. J. Nanotechnology 2012, 23, 105608.

Hello everyone! I’m here to tell you all about my trip to Frankfurt, Germany for the 27th European Photovoltaic Solar Energy Conference and Exhibition!  I flew out of Toronto at 1pm on Saturday afternoon, and I landed in Germany at 6am Sunday morning; that’s 12am Toronto time. This was my first time travelling alone, so I was admittedly nervous about the whole experience. Flying alone into a foreign country where I don’t speak the language, and where I can’t read street signs, made the prospect of navigating my own way from the airport to my hotel a rather daunting task, but I made it okay!  At the hotel, I met up with the other members of the Photovoltaic Innovation Network (PVIN), and we set out to explore the city before our week-long conference. Frankfurt is one of the financial hubs of Europe, and it features hundreds of different banks from all over the world. It is a very international city, but also a very quiet one. At night, you don’t see too many people walking in the streets; living in Hamilton, and having spent time in Toronto, this is not something to which I am accustomed!

Frankfurt, being such an international city, made an appropriate setting for the conference. 4024 people from across 76 countries participated either by giving talks, presenting posters, or simply listening to the presentations. The conference brought a lot of different people together, and with them came a lot of different ideas. During the first few days, the presentations focused on solar cell devices, and I must say that the diversity of solar cell designs is quite amazing. There were talks on traditional silicon cells, organic cells, heterojunction cells, multijunction cells, Dye and Hybrid cells, concentrator systems and so much more! My own work involves silicon, so I was particularly interested in these talks. Silicon has been around for a long time in photovoltaics, and it is a very mature technology. I observed that a lot of the current interest in silicon is not about improving devices, but about finding ways of making them cheaper while maintaining the same performance.  For example, there were many talks on replacing the silver in silicon cells with cheaper metals such as nickel and copper. While silver has nice electrical properties that make it attractive for use in solar cells, it is also expensive and the price is somewhat unpredictable.

Later into the week, the presentations focused on the ‘big picture’ issues of solar energy. There were talks on large-scale photovoltaic power plants, grid integration, manufacturing and processing, and solar cell markets, just to name a few. These talks were interesting because they covered issues that we don’t often think about at the research level. For one, we often don’t consider the manufacturability of the devices we make in the lab. It is one thing to be able to make high efficiency solar cells one at a time in a laboratory, but it is quite another to be able to produce them in higher quantities at a large-scale factory. As a researcher, the talks I saw later in the week really put things in perspective. I saw that solar energy is not just about the research; research is only the first link in a long chain. Included in the chain are the manufacturers that mass produce cells, the engineers who build and install the systems, and the policy makers that study and regulate the deployment of these systems. There are so many contributors from across numerous disciplines working in solar energy, and the conference really reinforced that idea in me.

I must say that my favourite presentations were those by Dr. Harry Atwater from the California Institute of Technology, and Dr. Martin Green from the University of New South Wales. Both men are very prominent researchers in the field of photovoltaics, and each lead a large group of graduate students and post docs that work at the frontier of photovoltaic research. Dr. Green in particular has done some of the pioneering work in silicon cells, including making a cell that is 25% efficient. This cell holds the world record for efficiency! A neat little bit of trivia is that Dr. Green graduated with a PhD from McMaster University, where I did my undergrad and am currently working on my Master’s degree. The talks given by Drs. Atwater and Green focused on the exciting work being done to incorporate the field of plasmonics into photovoltaics. Plasmonics is a field that deals with the interaction of light with nano-sized metal structures, and the strange phenomena that can result. For example, thin sheets of metal with nanoscopic holes can be made to transmit light in one direction, but not in the opposite. For a solar cell, this means that light could enter a cell, but not escape it. A useful application, indeed!  As solar cells are made thinner, in a push to reduce cost and the amount of material used, their ability to capture light is compromised. Techniques for manipulating and trapping light then become necessary in order to maintain comparable performance with thicker cells. The field of plasmonics happens to be brimming with these techniques. I should mention that my own research involves plasmonics. I am working with ultra-thin silicon cells, and using nano-sized particles of silver as a scheme for light trapping. This is why I was especially interested in these talks. Seeing Drs. Atwater and Green speak at the conference was truly a pleasure! Considering that they are co-authors on many of the research journals that I read, it felt like I was at a concert seeing my favourite musician play!

Plasmonic nanoparticles.

 

Alongside the conference there was a solar energy exhibition, in which companies and research institutes ran booths that showed off what each had to offer. Obviously there were many companies offering just solar panels, and some had put a decorative spin on their design. For example, I saw one company that had designed the cell to have a waterfall trickling down it! Definitely something that would look nice in a backyard! Other companies were offering equipment for research or manufacturing, and these booths were the most prominent at the exhibition. The most impressive booth, in my opinion, was from a company that had actually brought a solar cell assembly line into the building. There were periodic demonstrations in which cells would be produced, ready to be used in a panel. The operators were quite secretive about the assembly line, and photography was prohibited. Our own NSERC Photovoltaic Innovation Network (http://www.pvinnovation.ca) also had a booth at the exhibition, which displayed posters that highlighted the research that we do, and the Universities and companies that are involved. Manning the booth was one of my favourite parts of the trip. At the booth, we (representatives of the Network) were able to talk one-on-one with so many interesting people, and teach them a little about what we do in Canada, and what we have to offer. We talked with students, with members of industry, and other researchers that were interested in our work. The PVIN was (to my knowledge) the only Canadian presence at the conference. I felt truly honoured to be standing there at an international convention, representing our entire country and the research that we do, all while piquing the interest of experts from all over the world. It was an absolutely amazing experience. Being there in person also showed me that interest in solar energy is a truly global phenomenon. It’s really no surprise though; the sun is essentially an unlimited source of energy!

Overall, my trip to Germany was a fantastic experience. I learned a lot at the conference, talked with many interesting people, and made some new friends with other members of the Network. I was very grateful that we all stayed in the same hotel together. Very few people had a working cell phone, so organizing trips for dinner or walks around the city would have been a nightmare had we not stayed under the same roof. The city of Frankfurt was a neat place, and according to the locals, very boring! It was mostly banks and retail stores, but we always found something to do and were never bored. Aside from the conference, food was the highlight of the trip! I don’t think I will ever be able to eat schnitzel again, because it would just pale in comparison to authentic German schnitzel. Although the trip was fun, it was also exhausting, and after a week of being away, I was excited to get home. As I mentioned before, this was my first time travelling by myself and I learned a very valuable lesson: indirect flights are no fun! I flew from Frankfurt to New Jersey, and then I had to get a taxi to New York, where I could fly back to Toronto. After 19 hours of travelling and waiting and four airports later, I finally arrived home safe and sound at Pearson! I will definitely choose my flights more wisely in the future!

Suffice to say, I really enjoyed Germany and the conference, and can’t wait for the next one! Before I go, I’d like to thank Jennifer and Sandra for all of their help in organizing the trip and making it possible! Dankeschön!

-Kevin Boyd (Year 1 of M.A.Sc in Engineering
Physics at McMaster University, Hamilton Ontario)

Scanning electron microscope image of endview of Solar3D prototype

Solar3D Inc, a small research company founded in 2010, has recently fabricated a working prototype of a three-dimensional (3D) silicon solar cell [1]. Conventional solar cells employ a 2D geometry for capturing light. That is, light enters the cell through a 2D plane and is absorbed inside. A 3D solar cell uses 3D structures (the ridge-like structures pictured above) to capture light. An obvious advantage of this geometry is that there is a greater surface area for light absorption, and thus more light can enter a cell. The concept of a 3D cell is not new; cells that use thin nanowire structures to capture light have been known and studied for some time now. However, to the author’s knowledge, Solar 3D’s cell is the first of its kind to employ the ridge-like structures pictured above. Solar3D claims that their cell design offers many advantages over conventional 2D cells [2].

Firstly, conventional cells suffer from unavoidable reflection losses. Techniques exist to reduce these losses, but inevitably some light is always reflected away. A 3D cell is not immune to these losses either, however by virtue of the ridge-structures in such a cell, reflected light may be bounced back and forth between adjacent ridges, increasing the chances of it being absorbed. As well many 2D cells have metal contacts on the front to harvest the electrical current created by sunlight; these contacts are not transparent, so they block some of the sunlight from reaching the cell. In Solar 3D’s cell, the metal contacts run below the light-capturing ridges so that light-absorption is not compromised.

Another advantage offered by Solar 3D’s cell are thin absorbing regions. In a conventional silicon cell, the cell is made relatively thick to promote light-absorption. However, if a cell is too thick the electrons generated by sunlight may not make it out of the cell before being reabsorbed. Solar 3D’s cell overcomes this by using many thin absorbing regions. The thinness allows electrons to be efficiently collected, and the fact that there are many of these regions allows light to be efficiently absorbed.

Finally, Solar3D claims their cell has superior light-collection throughout the day (pictured above). Conventional cells operate most efficiently when the sun is directly overhead. This means that these cells will only perform optimally for a small part of the day. Many solar cell installations mount cells on trackers so that they can follow the sun throughout the day and overcome this disadvantage. According to Solar3D, their cell can collect light effectively over a range of angles, obviating the need for tracking systems, and allowing their cells to operate efficiently throughout most of the day.

The company fabricated their cell in July, 2012 and so far have not released any concrete details about the prototype’s performance. According to Solar 3D’s Director of Technology, Dr. Changwan Son, “When measured relative to a conventional solar cell design, our working prototype produces electricity beyond our previous expectations. First, we fabricated our working prototype. Then we created a simple cell based on the conventional design, using the same fabrication environment, to serve as a control sample. By measuring the side-by-side power output of both cells, we were able to determine the relative performance under a number of conditions, ranging from bright sunlight to lower, diffuse light. In each test, our 3D Solar Cell consistently outperformed the control cell and produced at least 2½ times the amount of electricity under the same conditions.” Unfortunately, the company does not provide any information on what particular “conventional solar cell design” they are comparing their 3D cell to. In the context of silicon, a “conventional cell” can refer to a myriad of devices covering a broad range of performance, and so these claims are rather ambiguous. The company has stated that simulations they have run on their cell design show that it should have an efficiency of 25.47%. This is a rather ambitious claim, considering that the record efficiency achieved in practice for a silicon cell is 24.7% [3]. The top 10 commercially available silicon cells have efficiencies ranging from 19.1%-22.5% [4]. Solar3D has not yet quoted an efficiency for their working prototype.

According to Dr. Son, Solar 3D’s next step is to improve the fabrication process so that they can drive down the cost of manufacturing their 3D devices. Son says “We believe that the result will be a 50% reduction in the cost of solar electricity. Perhaps the installed system cost savings will be even greater.” Again, this is a rather ambitious claim, considering how remarkable a 50% reduction of cost would be for solar energy. Solar 3D’s cell is certainly an interesting design, and the purported advantages it offers (mentioned above) are quite plausible. However, until the company releases detailed performance characteristics for their device, it is difficult not to remain skeptical regarding the company’s more ambitious claims.

-Kevin Boyd (Year 1 of M.A.Sc in Engineering Physics at McMaster University)

 

 

References

[1]. http://www.pv-tech.org/news/solar3d_reveals_working_prototype_of_3d_silicon_solar_cell

[2]. http://www.solar3d.com/technology.php

[3]. http://www.sciencedaily.com/releases/2008/10/081023100536.htm

[4]. http://www.renewableenergyworld.com/rea/news/article/2012/03/sunpower-tops-in-mono-c-si-solar-cell-efficiency

New research has shown that wrinkles on the surface of an organic solar cell can not only help boost performance considerably but can also be straightforward to implement, perhaps bringing organic solar cells one step closer to wider-scale commercial development.

The recent article in Nature Photonics states that the researchers took their inspiration from the natural world where some of the most basic light-harvesting structures rely on the small-scale variation in the morphology of surfaces.  A wide variety of light absorption enhancing surface structures are possible but many of those examined so far in the research literature require complex laboratory techniques. In some cases, this limits the potential for future commercialization.

In contrast to this research are surface structures like wrinkles and folds. They are something that occurs naturally as a material responds to stresses and strains and they may therefore be a cheap but useful way for improving the light-harvesting capabilities of certain types of solar cells.

The wrinkles on the surface of an organic solar cell bends light into the solar cell, forcing it to travel a longer distance inside the cell and enhancing absorption (Picture credit: Ref. at bottom).

The technique is conceptually straightforward.  Stresses and strains are applied to a substrate such that it develops wrinkles and folds on its surface. The organic solar cell is then deposited on top of this substrate and the surface pattern is imprinted into the solar cell. This allowed the Princeton researchers to create a solar cell that produced 47% more electric current than a comparably flat surface.

So next time somebody tells you that wrinkles are a bad thing; you can make sure to correct them.

-Erik Janssen

(Engineering Physics, MASc, Year 2 at McMaster University)

Article:

Wrinkles and deep folds as photonic structures in photovoltaics. Nature photonics, Vol 6. May 2012.

http://www.nature.com/nphoton/journal/v6/n5/full/nphoton.2012.70.html