Novel hybrid materials for improved photovoltaic device efficiencies

In principle, photovoltaic (PV) devices could meet all our energy requirements in a sustainable way: the earth's surface receives enough light energy per hour to power the entire human population for one year. However, the current capital expense of conventional photovoltaics is too great to be competitive, and the volume in which they can be produced is much too small to make a serious dent in our electricity generating needs. As a consequence solar photovoltaics (PVs) account for < 0.1 % of our energy generation. Whereas conventional silicon-based PVs have high manufacturing costs and involve energy-intensive fabrication, organic PVs can be processed using high-volume roll-to-roll printing technology, promising large-area, cheap photovoltaic films of flexible backing material that could be used in principle to coat windows, walls and roofs. Such devices are already being produced commercially for high-mobility, low-power applications such as rucksacks comprising flexible organic PV devices to charge mobile phones and similar products. The external power efficiencies of polymer-based PVs have increased dramatically from sub-1% in the mid-90s to <6% in a period of 10-15 years. One of the most promising systems has involved a blend of two molecular materials P3HT (a polythiophene long-chained molecule) and PCBM (a functionalized fullerene). The preparation of these involves limited segregation that leads to a bicontinuous structure on the lengthscale of around 10 nm, such that electrons and holes can be separated relatively efficiently at an interface between the two materials. The efficiency of the P3HT/PCBM system is limited by the relatively large band-gap of P3HT, which renders the optical absorption inefficient at the red end of the solar spectrum. Consequently, new polymer materials are being developed, but are usually patented by companies and expensive to synthesise, that have lower band-gaps extending the absorption performance to red/infra-red wavelengths. We are developing an alternative approach using hybrid structures to increase the local electric field and to enhance the optical absorption. These hybrid materials will then be used to fabricate prototype photovoltaic devices allowing an assessment of the power conversion (solar-to-electricity) efficiencies. In the first instance, we hope to develop photovoltaic devices with efficiencies of greater than 6 %, comparing favourably with the market leaders. This will allow further capital investment to be sought with the long-term aim of larger scale applications being realised once efficiencies reach 9-10 %.

The manufacture of photovoltaic (PV) cells has grown significantly over the last decade, due to an urgent and growing demand for clean, renewable energy sources. Organic PV devices based on polymers are generating intense global effort due to their potential cheapness and ease of processing on flexible substrates e.g. plastic coatings. Commercially competitive flexible films will need to achieve 9-10 % efficiencies at < 1$ /watt with a lifetime of 5-10 yrs. Current OPV cells that are based on accessible and cheap organic polymers suffer from two fundamental problems: (i) light is inefficiently absorbed across the solar spectrum; (ii) incomplete conduction pathways lead to significant energy loss and poor efficiency. Our project hypothesis developed by addressing these two issues directly. The proposed device will require: (i) improved solar absorption (ii) excellent mobility conduction pathways (iii) excellent charge separation dynamics Support from the Follow on Fund will allow the project team to focus on the feasibility of accessing high PCE (> 6%) PV devices based on these hybrid materials. The key aspects to address: (i) supporting the patent application by providing detailed patent exemplification through additional experimental work and device assessment; (ii) ensuring commercial exploitation by developing interaction with relevant industrial partners via Fusion IP and the Technology Transfer Office. The work will therefore have a major impact on the industrial sector, primarily in terms of companies that manufacture and supply photovoltaic materials. In addition, the flexible nature of these OPV materials render them attractive to more specialist secondary industries interested in developing 'smart' fabrics/materials and portable electronics. To re-iterate, success in this Follow-on-Funded project will seed the diverse exploitation of new hybrid materials, based on relatively cheap precursor components, towards commercial realization. Following securitization of the IP position and routes to commercial exploitation, we will seek to disseminate key components of the fundamental science to the wider community by publication within high impact journals. This process will obviously require close cooperation and endorsement from future industrial partners who will undoubtedly mutually benefit. The case for overall societal benefit is compelling as the full commercial exploitation of this discovery will lead to higher efficiency energy production, reduced carbon footprints and a reduction in our collective reliance upon fossil fuels. Additional benefits could also be realized in smart technologies. The strategic ramifications of this project offer coherence with current governmental policy, since the UK has targets to reduce emission by 80% and to contribute 15% renewable energy to the EU by 2020. Action is required now to address this commitment. The UK Renewable Energy Strategy estimates that 100bn worth of investment will be required in order to meet these targets. The Renewable Obligation legislation also requires all electricity providers to source a proportion of their energy from renewable supplies and will obviously require rapid development of new technologies in the near future. Dr C. Griffiths (Fusion IP commercial manager) has already been involved in detailed discussions regarding the long-term commercial development of the project and will continue in this role, giving support and advice on the best way to develop the technology and route-to market corroborated with updated market research from Mr A. Cheer. Established links with Dr V. Stevenson of the Low Carbon Research Institute (Cardiff University) will provide guidance on future exploitation of our materials to real-world applications, with consideration of environmental factors of device fabrication and encapsulation (minimizing moisture ingression; optimizing photostabilities; ease of processing).