Light Energy Converters into Electric or Chemical Energy
Research and Development of Photoelectrochemical Light Energy Converters Based on Organic Semiconductors Using the Principles of Photobionics
Tech Area / Field
- NNE-SOL/Solar Energy/Non-Nuclear Energy
8 Project completed
Senior Project Manager
Russian Academy of Sciences / Semenov Institute of Chemical Physics, Russia, Moscow
- VNIITF, Russia, Chelyabinsk reg., Snezhinsk
- Universidad Autonoma de Madrid / Department of Organic Chemistry, Spain, Madrid\nJohannes Kepler Universitat Linz / Linzer Institut for Organische Solarzellen, Austria, Linz\nArgonne National Laboratory (ANL), USA, IL, Argonne\nLawrence Livermore National Laboratory / University of California, USA, CA, Livermore
Project summaryThe basic purpose of the project is the creation of new technologies to transform light energy into electric or chemical energy in systems on organic semiconductors and the development of a laboratory-scale photoelectrochemical converter with a quantum yield on a current of at least 40 percent.
Extensive research on the properties of various types of organic pigments carried out under the direction of Professor G.G.Komissarov (Laboratory of Photobionics, Semenov Institute of Chemical Physics, Russian Academy of Sciences) has shown that tetrapyrrole compounds similar to plant leaf pigments are most promising in this respect, due to their high photoactivity, chemo- and photostability, and also their low cost. The unique variability in molecular structure of these pigments allows us to select compounds with demanded macroscopic properties over a wide range. At the same time, the opportunity of vacuum sublimation of tetrapyrrole compounds makes processes of purification of the pigments from impurities and of manufacturing thin-film photoactive electrodes highly technological and well reproduced. For several years, participants of the project carried out research on consecutive changes in structure of tetrapyrrole molecules - the introduction of various substitutors, modification of the central group of atoms, changes of groups of symmetry and the introduction of extra ligands. That made it possible to raise the quantum yield on a current of the pigmented film-electrodes up to 22 percent and to determine phenomenological relation between the efficiency of transformation of light energy in films and the structure of molecules of pigments. Further research in this direction will certainly enable researchers to formulate ways for direct synthesis of the most highly effective compounds. In order to do that, it will be necessary to investigate a broader range of tetrapyrrole compounds. Especially interesting are molecular structures with extraligands on the central atom of metal and mesopositioned substitutors in the macroring conjugation system. Considerable increasing in quantum yield of photoelectrochemical converters is expected using thin-film systems up to monomolecular layers produced by the Blodget-Langmuir method, and to optimize the structure of pigment films.
Within the framework of the proposed research project, the area we have chosen to focus on is based on the idea of the pulse creation of a pool of the charged superficial states (similar to processes in chlorophyll aggregates in plants) at the moment of a short pulse of light, and the subsequent slow charge transfer to electrolyte. Our preliminary experiments have shown, that during pulse photoexcitation of a pigment takes place an effective colonization of superficial levels of a pigment film, formed by adsorbed from electrolyte electron acceptors. Density of superficial traps may reach 1015 cm-2, and period of their colonization is less than 10-6 sec. In a dark period there is much longer process (> 10-4 sec) of the discharge of the surface with electron transfer in electrolyte, and efficiency of the process as a whole is much higher, than in a steady mode.
The proposed program of work within the project contains three basic stages:
1. The comparative analysis of photoelectrochemical properties of the most specific tetrapyrrole compounds (more than 30 derivatives of porphyn and phtalocyanin). Quantum mechanical calculations of electronic density distribution in molecules of investigated compounds with extreme parameters. Elucidation of the relationship between molecular structure of tetrapyrrole compounds and photoelectrochemical properties of their films by analysis of the anew received results and our own databank. That will allow us to create pigmented electrodes with predicted optimum highly effective structure.
2. Optimization of the solar energy conversion process in photoelectrochemical elements on organic semiconductors using a new method of formation of photosensitive films and the modulated light flow. On the basis of the received experimental data and theoretical development we hope to increase efficiency of solar energy conversion in those systems by 2-fold and to perfect the quantum yield of up to 40 percent.
3. Development of a laboratory-scale pulse converter of a solar energy on the basis of tetrapyrrole compounds. An expected quantum yield is 40 percent.
Completing the proposed research program will allow us to solve a number of fundamental problems of organic semiconductors physics, first of all, to find out the relation of photoactivity of pigments in aggregated state with their molecular structure. At the same time, applied aspects of the program can become a basis of a new direction in the solar power engineering.
We are confident that this program will be a success: some of our participants have spent 30 years working on this topic. The theoretical concepts and experimental approaches in our proposed research project are based on more than 150 scientific publications on the modelling of photobiological processes, as well as on the photoelectrochemical converters of solar energy.
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