Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics 2018 (AP-HOPV18)
DOI: https://doi.org/10.29363/nanoge.ap-hopv.2018.056
Publication date: 27th October 2017
Organic-inorganic hybrid devices such as perovskite and dye sensitized solar cells (DSSCs) are promising candidates for future renewable energy applications[1][2]. Fabrication using solution processing and the utilization of low-cost materials promise low-cost and scalability. However, despite more than two decades of work on DSSCs (and more recently perovskites), stability and reliability challenges have hindered commercialization. DSSCs suffer from stability problems because of solvent evaporation, electrolyte-driven oxidation of electrical contacts, and dye degradation. Among these challenges solvent evaporation is perhaps the most severe and numerous solutions have been proposed. Examples include the use of non-volatile solvents/ionic liquids, polymer electrolytes and substituting the liquid electrolyte with amorphous small-molecule solid-state hole transport layers. However, nearly all the solutions lead to lower ionic (or hole) conductivity when compared with acetonitrile and thus exhibit lower photovoltaic performance.
In this research we present progress towards the development of thermally-reversible liquid crystal (LC) based physical-gel electrolytes[3]. In particular, we utilize discotic LCs[4] (triphenylene HAT6 and HAT5) that form hexagonal columnar mesophases to form a three-dimensional interconnected network of liquid crystalline fibre bundles to make physical (non-covalently bonded) gel electrolytes. Gel-formation is achieved in-situ using capillary filling, allowing fabrication methods similar to conventional liquid electrolyte DSSCs. The iodide tri-iodide redox electrolyte is confined within the network, limiting bulk flow, but ionic diffusion within the network is not impeded due to phase separation between the gelators and electrolyte.
Gel formation is characterized using polarizing optical microscopy and differential scanning calorimetry. Measurements of ionic conductivity, diffusion coefficients and electrochemical impedance spectroscopy are performed and gel-based photovoltaic devices are fabricated. In comparative studies, the devices exhibit significantly improved stability, competitive ionic conductivity and improved electron lifetime in the mesoporous TiO2 (˜8.4 ms in reference liquid electrolyte and ˜11.4 ms in the physical-gels) due to charge screening by the LC fibers. Our results show that LC-based self-assembled gelators are promising materials for DSSC applications[3] and ongoing work on understanding the driving mechanisms of gel formation as well as the parameter space of compatible solvents is discussed.
[1] B. E. Hardin, H. J. Snaith, M. D. McGehee, Nat. Photonics 2012, 6, 162.
[2] W. Zhang, G. E. Eperon, H. J. Snaith, Nat. Energy 2016, 1, 16048.
[3] A. A. Khan, M. A. Kamarudin, M. M. Qasim, T. D. Wilkinson, Electrochim. Acta 2017, 244, 162.
[4] R. J. Bushby, K. Kawata, Liq. Cryst. 2011, 38, 1415.
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International Conference on Hybrid and Organic Photovoltaics
International Conference on Hybrid and Organic Photovoltaics (HOPV) is celebrated yearly in May. The main topics are the development, function and modeling of materials and devices for hybrid and organic solar cells. The field is now dominated by perovskite solar cells but also other hybrid technologies, as organic solar cells, quantum dot solar cells, and dye-sensitized solar cells and their integration into devices for photoelectrochemical solar fuel production.
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