Solar Energy Conversion

Niyazi Serdar Sariciftci`s research focuses on "organic semiconductors". In the field of organic photovoltaics, he discovered photoinduced electron transfers in p-conjugated organic semiconducting polymers and Fullerenes and went on to write a seminal article in 1992 in which he described "bulk heterojunction polymer solar cells" for the first time. Even at the start of this groundbreaking research in 1992, Sariciftci developed two different types of polymer solar cells: a) two-layer solar cells with thin films of organic charge donors and acceptors, and b) bulk heterojunction solar cells, in which organic charge donors and acceptors are mixed, thus giving rise to a large interface layer throughout the entire volume of the cell. Organic polymer solar cells are distinguished by the following specific advantages: The molecular nature of organic semiconductors enables the modification of properties through chemical synthesis; the cells can be produced on large surfaces without a bottleneck in materials (chemical abundance); low-cost production using roll-to-roll printing techniques; the mechanical flexibility of polymer materials and thus the ability to integrate them directly into various construction components and surfaces. At present, the conversion efficiency of organic solar cells worldwide has reached approximately 10% (i.e. one tenth of solar energy is transformed into electric power). This value is still lower than that of conventional crystalline silicon cells by a factor of 2, but it is already on par with the efficiency of amorphous silicon cells. Sariciftci is now working with new concepts and ideas in the field of organic solar cells in order to design innovative architectures and methods using new, biodegradable materials. In this context, it is important to remember that renewable energy sources face major challenges with regard to storage and transport. Wind and solar energy are subject to the disadvantage that it is not possible to synchronise energy production and demand. Therefore, storing these types of energy remains a key challenge. In addition, wind and solar energy have to be transported over large distances between the optimal places of generation and consumption. One effective way of storing wind and solar energy is to transform them into "chemical fuels." The energy density of petrol is approximately 46.4 MJ/kg (12.9 kWh/kg), which is far higher than that of a lead-acid battery (35Wh/kg). Filling an average-sized tank with petrol is equivalent to charging a 12 V battery with 1 million amperes. The weight of the tank of petrol is approximately 30 kg. In order to store the same amount of energy, an electric battery would have to weigh roughly 2,500 kg. These considerations led Sariciftci to the conclusion that it is necessary to transform and store chemical energy using hydrocarbons. The carbon dioxide necessary for this purpose can be taken from the air and exhaust gases, after which it can be transformed into a fuel. Fuels produced in this way are CO 2 -neutral and thus also meet the need for sustainability. This approach would solve two problems at once: the challenge of storing solar energy as well as that of CO 2 emissions. The Wittgenstein Award will enable Sariciftci and his research team to continue exploring this new field of research - "CO2 recycling in chemical fuels using solar energy" and to develop it into a new research competence in Austria.

This work has been targeting on transforming solar energy into useful energies for the mankind. The solar energy which hits the world day by day is over 150.000 Terawatts. The human civilization needs today around 15 Terawatt. This vast, renewable and abundant source of energy will be needed to ensure the survival of the human civilization over the next century. There are three main possibilities to convert solar energy for human use: a.) The conversion of solar energy into heat (solar thermal conversion): This is a wide spread technology today in use and has not been targeted during the Wittgenstein Prize Project of Prof. Sariciftci. b.) The conversion of solar energy into electricity (solar photovoltaics, PV): This technology is today widely based on Silicon solar cells with power conversion efficiencies around 20%. In this project we have investigated new organic and bioorganic as well as organic- inorganic hybrid composite materials for photovoltaic solar energy conversion. Such new organic materials perform today at the end of this project (2018) with around 10% power conversion efficiency in our laboratory scale devices, whereas organic-inorganic hybrid materials (perovskites) perform around 15% power conversion efficiencies. There is ample scientific evidence that such materials can be synthesized in a large scale and deployed in flexible, large area surfaces as paint like coatings. Such a light-weight PV cell, fabricated by printing or coating technologies, can indeed have an impact on photovoltaics of the future. c.) The conversion of solar energy into chemical energy (solar fuels, artificial photosynthesis): In this technology we use the solar energy to convert CO2 back into an artificial synthetic fuel. Burning such a recycled fuel emits exactly the same amount of CO2 into the atmosphere which it has converted during its synthesis. Therefore, this conversion of CO2 into hydrocarbons is considered as "CO2 neutral". This is in principle the same process which has been used for the last 3.5 billion years in the natural photosynthesis. In this project we have investigated organic and bioorganic as well as organic-inorganic hybrid composite materials for solar energy conversion into useful chemicals and fuels by recycling CO2 gas. The resulting products range from methane as the simplest hydrocarbon all the way to formic acid, methanol, butanol. The great advantage of solar energy conversion into chemical energy is clearly in the possibility of large scale storage of the solar energy in such chemicals. Photovoltaic energy as well as wind energy always need a storage due to their instability and discontinous nature. Converting renewable energies in useful chemical fuels solves this problem of storage and transport immediately and implicitly.