The development of high-efficiency low-cost renewable energy sources is one of the most pressing research challenges today. Two promising technologies in this area are photovoltaics (PV) and Solar Fuel generation systems. PV work by absorbing sunlight to generate electrical charges that are then collected in an external circuit. Solar Fuel systems work by absorbing sunlight and then using the charges produced to drive redox chemistry to produce chemical fuels from readily available starting materials, for example splitting water to produce H2, which is a powerful fuel. But the cost to efficiency ratio of both these technologies is too high currently. In order to drive the price of these technologies down to match fossil fuels, fundamental breakthroughs are required in the way these systems harness solar energy. This project seeks to tackle this challenge by building on recent insights into quantum mechanical processes in organic semiconductors to improve the efficiency both of current and future PV systems as well as put in place new design ruled for high-efficiency solar fuel generation systems. At the heart of many kinds of PV and Solar Fuel systems are interfaces between organic and inorganic semiconductors. The role of these interfaces, known as heterojunctions, is to separate opposite charges, hole and electrons, from each other and prevent their recombination. We will use the latest breakthroughs in ultrafast laser spectroscopy to study these interfaces and develop novel structure that efficiently separate charges. The biggest energy loss in PV is a process known as thermalization. This refers to the fact that the absorption of a high-energy photon generates one electron-hole pair just as the absorption of a low-energy photon does. The extra energy of high-energy photons above the bandgap is lost as heat. This problem affects all commercially deployed PV today and has long been considered a fundamental loss. Indeed it leads to what is known as the Shockley-Queisser limit on efficiency, which is 33% for an idea PV of bandgap 1.1eV. Here we will use a unique quantum mechanical process in organic semiconductors called Singlet Exciton Fission, to overcome this loss. Singlet Fission allows two electron-hole pairs to be generated in certain organic materials when a photon is absorbed. We will design new ways by which these electron-hole pairs can be harvested at the organic/inorganic interface, leading to improved efficiencies. The methods and structures we will develop using this process would be compatible both with current and future PV technologies, allowing them to over come the Shockley-Queisser limit on efficiency. This could dramatically improve the efficiency of PV and help bring about their wide scale deployment.

Organic and other types of solution-processed solar cells are a highly promising alternative to conventional silicon-based photovoltaics (PV) as a lightweight, flexible, disposable and truly building-integrated PV technology with extremely quick energy payback. However, their limited stability has now been widely recognised as a common bottleneck for their commercialisation, with exposure to various environmental factors (e.g. light, heat, oxygen, humidity) leading to rapid losses of their performance, the origin of which often remains widely unclear. Fullerenes have been ubiquitously used as an electron acceptor and transport material in organic solar cells (OSCs) in the past two decades. Only until the last 3-4 years, non-fullerene acceptor materials have been brought to the forefront of the development of OSCs as a more efficient, lower-cost and more versatile alternative to fullerenes, with the performance of fullerene-free OSCs already significantly exceeding that of fullerenes-based OSCs. Nevertheless, the majority of research efforts to date have only been dedicated to further optimising their efficiency, leaving a clear gap in the understanding of their stability and degradation mechanisms, another key consideration for their commercialisation. This proposal is designed to address three very important yet largely unanswered questions in the development of stable fullerene-free OSCs: 1-What are the mechanisms causing the degradation of fullerene-free OSCs; 2-Can we understand these degradation mechanisms both comprehensively and quantitatively; and 3-What controls these degradation mechanisms and how to address them? To answer these questions, this proposal will develop a new research methodology to study OSC degradation, which has not been established previously. By performing time-resolved and inter-correlated optical, structural and functional analysis of PV films and devices degraded in a locally-controlled environment, this methodology is capable of capturing the real-time information of the fundamental processes leading to device performance losses during the degradation process, thereby establishing a quantitative relationship between the degradation mechanisms and the resulting OSC degradation behaviour. Specifically, the evolution (i.e. time-resolved) of several advanced, performance-determining device parameters, as well as that of chemical and structural changes during the same degradation process (i.e. inter-correlated), will be recorded and further analysed in order to reconstruct the OSC degradation behaviour. Only fullerene-free OSCs will be studied in this project, but the new methodology can be universally applied to study other types of solar cells, such as polymer:fullerene, quantum dots, dye-sensitised and perovskite solar cells. A core focus of this project is the quantitative analysis of the impacts of major degradation mechanisms of fullerene-free OSCs as a function of their material and device design. The PI has already led the research efforts in quantitatively investigating the degradation of fullerenes and their impacts upon OSC stability, which laid the foundations for the development of the new research methodology proposed here. Based on the quantitative knowledge acquired, this proposal also aims to develop comprehensive material and device design rules capable of guiding the systematic optimisation of the stability of fullerene-free OSCs. This proposal will build upon the established research expertise and facilities in energy materials and devices at Cardiff University, in close collaboration with Swansea University and Imperial College London. The project will be carried out in partnership with 1) Eight19 Ltd., a UK-based SME specialising in the commercialisation of OSC products; 2) NSG group, a UK-based, world-leading company in glass and glazing products (e.g. glass-based PV products) 3) Armor group, a France-based company specialising in printing and coating technologies.

Our research aims to develop plastic films or coatings that change the colour and other characteristics of the light that passes through them, not by absorbing certain wavelengths of light, as a simple colour filter would, but by converting light of one wavelength to another without losing any energy. Solar cells offer an example of why this would be useful: conventional silicon solar cells are more efficient at collecting the energy of red light than they are of blue light. So if we coated the solar cell with a film that would convert every blue photon into two red photons, without losing any energy in the process, in principle we could make the silicon solar cells 30% more efficient. Our previous research at Cambridge has shown in principle how this could be done. Certain organic semiconductors will absorb a blue photon to produce an electron-hole pair, which then splits into two. Normally these two electron-hole pairs would annihilate and the energy would be lost, but if we can arrange for the organic semiconductor to be in molecular contact with an inorganic semiconductor quantum dot, then the electron-hole pairs can migrate to the quantum dot, where they will recombine and emit two red photons. The problem we now want to solve is to work out how to turn this idea into a practical product that we can manufacture on a large scale. We need to be able to make semiconductor nanocrystals that won't clump together, and to coat them with a very thin layer of the organic semiconductor so the two materials are in molecular contact. Then we have to disperse these tiny particles in a clear plastic film, which we can use to coat a solar cell - and the whole process has to be designed so that it doesn't increase the cost or complexity of making the solar cell too much. This coating for solar cells is just one example of the potential there now is for taking the latest materials from the laboratory with novel and interesting optical properties and turning them into useful products. Another example is provided by thin sheets of semiconductors only a few atoms thick. These can be very efficient at absorbing light (for example from a light emitting diode) and reemitting it as a single, purer, colour. This will help us make better optical communication devices and display devices. But once again, we need to learn how to encapsulate and embed these tiny, ultrathin sheets into a plastic film without them sticking together in stacks. The key to solving these manufacturing problems is understanding the factors that make these tiny particles and sheets stick together and what treatments could keep them apart - often this will involve sticking special molecules to their surfaces. In the final products, these particles and sheets will be dispersed in a plastic sheet, and we need to understand how, as the plastic film dries or sets hard, the drying process affects the particles, and whether the processes that take place in the drying film makes the optical effects we're looking for less effective. We will be studying the films we make with techniques that allow us to see the individual molecular layers around the particles, as well as how well the particles are dispersed. In this way we'll understand the rules for manufacturing these sorts of films. By the end of the project, we aim to be able to work with solar cell manufacturers to test our idea in the real world and get to the point where a product can be commercialised. If we are successful, we'll have demonstrated that we can go from understanding the fundamental science of these optical and electronic effects in these new kinds of materials to make useful products that will benefit UK industry and help solve problems of climate change.

The first electronic devices using organic semiconductors have just entered the market: many displays of mobile phones consist of organic light emitting diodes (OLEDs). However, these OLED-displays are considered only the first wave of organic electronic (OE) products, with organic solar cells and organic lighting expected to follow soon. Organic solar cells are currently a very active field of research, because they have the potential to become a very cheap, large area, and flexible photovoltaic technology. They furthermore can have unique properties like custom-made shapes, semi-transparency and different colours, considerably expanding the potential market to areas where current technologies are struggling. Records for conversion efficiencies have reached values above 10% and lifetimes exceeding 10 years in the laboratory, i.e. passing important milestones that are often considered as minimum requirement to become viable for commercial applications. However, one major challenge for industry trying to commercialise this technology is: for any kind of device using thin organic semiconducting layers, its electrical and optical properties strongly depend on molecular arrangement in the organic layer, in particular for organic solar cells. To a large extent, the interdependencies between molecular structure, processing, morphology in the thin organic film, and the device properties is a black box. The current approach for improving solar cells is to make more new molecules and to run an extensive process optimisation and device testing, but there are nearly unlimited options of organic chemistry and many degrees of freedom in process parameters. This nearly trial-and-error process is consuming time and money, as well as carrying the risk that the best organic semiconductors are discarded due to wrong processing. Our project will look into this black box in a close collaboration of four industrial partners (Merck Chemicals Ltd, Kurt J. Lesker Company Ltd, Eight19 Ltd, Oxford PV Ltd) and three academic partners (ISIS Neutron and Muon Source, Diamond Lightsource, University of Oxford) and subsequently develop ways to optimise the manufacturing of organic solar cells. This involves optimisation along the complete value chain, from the design and synthesis of organic semiconductors, the development of manufacturing equipment, to the final production of organic solar cells. If successful, this project will lead to a faster market introduction of thin film solar cells that have the potential to transform the way we use solar energy.

In November 2016 the UK Government mounted a technical trade mission to India. During this visit the delegation witnessed some of the worst aerial pollution in Delhi's history. At times the air quality was contaminated with 999 mg per cubic metre of particulates almost five times the emission consent of an iron making coke oven! India will be the World's largest economy potentially as early as 2030 requiring a total transformation in energy generation. At the Trade summit Prime Minister Modi detailed a vision for India to leapfrog other countries reliance on fossil fuels harnessing global science implemented locally. As such the timing of SUNRISE could not be better. SUNRISE is an ambitious programme to rapidly accelerate and prove low cost printed PV and tandem solar cells for use in off grid Indian communities within the lifetime of the project. SUNRISE will combine world leading UK research teams from Imperial (Durrant/Nelson), Cambridge (Friend), Oxford (Snaith) a key Indo UK research leader (Uppadaya at Brunel) with an internationally leading photovoltaic scaling activity (SPECIFIC IKC at Swansea University (Worsley/Watson)) and key Indian institutions notably IIT Delhi (Dutta/Pathak), NPL Delhi (Chand, Gupta), CSIR Hydrabad (Giribabu, Narayan), IISER Pune (Ogale), IIT Kanpur (Garg, Gupta). The research impact of scaleable and stable low cost metal mounted PV products will be supported by technology demonstration at five off grid village communities (each of up to 20000 people). The EPSRC JUICE consortium will support the systems integration and electrical storage elements to create real technology demonstrators using local manufacturing supply chains (Tata Cleantech Capital and Tata Trust). In addition to electrical infrastructure the SUNRISE partnership includes activity on gasification of farming/crop wastes (a major cause of the incredible pollution in Delhi in November 2016) and the SPECIFIC IKC will support the practical on site demonstration of photocatalytic water purification using a linked programme with the Gates' Foundation. A key driver for this project is not only demonstration of technology in real demonstration sites but the creation of a legacy of better Indian Industry/Institution collaboration through the creation of an Industrial Doctorate programme modelled on the success of the UK EngD programme started by EPSRC in 1992 and pioneered at Swansea.