Dr. Seamus Curran, Dr. Yorgos Marinakis, Dr. Nigel Alley,
Dr. Kang-Shyang Liao and Dr. Steven Walsh
Dr. Seamus Curran is Director of the Institute for NanoEnergy
at the University of Houston and CEO of C-Voltaics
Dr. Yorgos Marinakis. Nikos, University of Twente
Dr. Nigel Alley is a research scientist at the Institute for NanoEnergy
at the University of Houston
Dr. Kang Shyang Liao is a research scientist at the Institute for NanoEnergy
at the University of Houston
Dr. Steven Walsh, UNM Anderson School Regents professor MANCEF Board Member
The photovoltaic (PV) cell industry grew rapidly worldwide in 2010. This was due to the exceptionally steep learning curve that traditional, mostly silicon based, photovoltaic cells experienced caused rapid decreases in price and improved efficiencies. Photovoltaics also got a large boost from the green movement and smart-grid improvements promoting many countries and states to subsidise commercial and residential solar conversions. Now silicon based photovoltaic cell efficiencies are being captured at the module level and some government subsidy support is waning initiating a worldwide solar market to soften. Finally, economic crisis countries such as Spain and Italy, big supporters of solar integration, have severely curtailed support for solar energy.
The result is the top ten producers were recently ‘reshuffled’. The EBIT margins of these companies were all dropping or stabilizing, due to the downward price pressure. Yet between February 2008 and November 2011, polysilicon prices dropped 93 %, making the cost of solar-generated electricity competitive with fossil fuel-generated energy. The 2010 US solar module market alone represented $1.6 billion. The solar industry is at least stable. The solar PV marketplace is still dominated by Silicon based PVs however the industry is turning to other technologies and other substrates for innovation. Organic PVs may well prove to be a disruptive technology in the field in the coming years.
There are four general types of photovoltaic technologies defined by their substrate technology. Two are considered first generation solar cells: (1) crystalline Silicon based PV cells and (2) multi and single junction devices like GaAs. The two other thin film technologies typified by CdTe based PV are considered second generation PV. Organic based PV (OPV) is considered the third generation solar technology. The basis of competition in the Silicon crystalline PV marketplace is shifting from manufacturing capacity to price. That is, the industry’s revenue and profit leaders will shift from those companies that can ship the greatest volume at any price and quality to those that can produce most efficiently while improving on quality. It is the promise of OPVs where the speed of efficiency development and its unique properties are perhaps becoming more interesting commercially for nanotechnology developers.
OPVs can form conformal coatings and its base material is the most inexpensive. Yet today they are compromised in translating charges generated into electricity, which has damped any commercial appetite. The challenges commercially in the industry are in part that some companies launched their OPVs too soon when stability and module efficiencies never went beyond 5% were a major concern. The use of morphologically controlled nanomaterials and nano-thin films is changing this perception. We are seeing significant advances in champion cell efficiencies. A champion cell is one which reports an efficiency of a cell whose dimension is 1 cm2. However, whilst material concerns are very important, we must also recognize that building OPVs architecturally in a manner that works for silicon has been a problem. The field has focused on the material concerns and quite rightly for where it was over the last two decades.
New nanomaterial based OPVs are ultra-thin having an active layer (light absorbing semiconductor) ranging from 40-100 nm in thickness. Once a thin film becomes too thin, other optical and indeed commercial hurdles occur since it becomes semitransparent. Yet it is a factor that can also benefit commercially as they could be used on glasses in large buildings. This is somewhat a white elephant that has been used to bypass an important technical problem associated with these materials. Organic nanomaterials are poor electrical carriers characterised by low carrier mobilities.
A new OPV architecture is beginning has emerged to address this. OPVs are being built in a vertical fashion as opposed to a flat one as shown in Figure 1. In this new case, light is channeled down vertically through the thin film analogous to the way light travels in an optical fiber. However, unlike the optical fiber, the ultimate goal is to absorb as much light as possible.
On the left hand side of Figure 1 the electrodes and active layers are presented, generally no thicker than 200 nm. The active layer being <100 nm is illustrated in the center which is a bicontinous blend of two semiconductors yielding the bulk heterojunction and on the right is a sketch of the vertical arrays comprising a vertical architecture OPV cell where the active layer is sandwiched between glass substrates. The height of the glass substrates can be reduced to as little as 50 microns, but maintaining an ultra thin <100 nm active semiconductor layer can be problematic.
The result in OPV efficiencies are continuously improving, a 7.3% efficiency was recently achieved. Mitsubishi Chemical claims to have achieved 9.2 % through proprietary technology and announced a goal of 15% by 2015. The forecast of the OPV market will be limited by the low power conversion efficiencies of the technology and will only reach $159m by 2020. Though this scenario certainly is possible, we think the evidence suggests alternative much larger forecasts of OPV market scenarios that for a variety of reasons are at least equally as likely.
OPV technology power conversion efficiency has seen a very positive trend for the most part enabled by adapting the engineering approach applied to silicon PV technology, namely the multijunction and tandem architectures. Further the scalable design and flexibility of OPV cells is simply not available in first and second generation PV technologies. Finally OPVs are making headway in broadening the absorption range necessary to have higher currents, maintaining the voltage and improving the optical absorption. If OPVs can achieve champion cell efficiencies in the size range of silicon based PV modules and at a fraction of the price a truly disruptive technology will be realised.
Authors:
Dr. Seamus Curran
Shay is the Director of the institute for NanoEnergy (INE), Associate Professor of Physics at the University of Houston and CEO/Chairman of C-Voltaics, a nanotechnology and energy company. He is also a member of the Global Irish Network, a diaspora group set up by the Irish Government while he was named a a Tech All Star from the State of New Mexico Economic Development Department. He graduated from Trinity College Dublin in 1995 with a PhD in Physics, served as a postdoc at the Max Planck Institute, CNRS and Rensselaer, has published over 100 papers and has been cited over 2,500 with a h index of 21.
Dr. Steven Walsh
Steve is the Regents Professor at UNM’s Anderson School of Management. He has many business service awards including the lifetime achievement award for Commercialization of Micro and Nano technology firms from MANCEF. He has also been named as a Tech All Star from the State of New Mexico Economic Development Department and has been recognised by Albuquerque the magazine as a leader in service to the economic community. Finally, he is exceptionally proud of the Anderson School of Management Service to the Community Award.
Dr. Yorgos Marinakis
Dr. Yorgos Marinakis is a Ph.D. in Biology, a patent attorney and a Technology Entrepreneurship student at Nikos. He was the main author of the Organic Photovoltaic roadmap and an expert in disruptive technology based entrepreneurial action.
Dr. Nigel Alley
Dr. Alley is a research scientist at the Institute for NanoEnergy. He graduated with a Ph.D. from Dublin City University as a joint program between UH and DCU. He has published 15 articles, holds a number of patents and presented his work at international conferences.
Dr. Kang-Shyang Liao
Dr. Liao has been a research scientist at the Curran nanophysics group and Institute for NanoEnergy since 2008, after he graduated with a Ph.D. of Chemistry at Texas A&M University. He has published over 30 publications, numerous patents and presented at international conferences.