Storage of Electrons into Chemical Bonds: Towards Molecular Solar Electrical Batteries

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While photovoltaics has observed rapid growth in the last decades and utilization of solar energy becomes ever growing part of the total electricity produced by mankind, the lack of control over electrical output caused by fluctuation of solar irradiance is an inevitable drawback of the mass use of solar cells. Solar batteries, addressing intermittent production of solar energy, offer an elegant solution without the need of electricity transport and redistribution. In most examples solar cells are combined with rechargeable batteries (e. g. Li-ion, Pb) which increases the total weight and cost and leads to electricity losses. The approaches for molecular-based storage of light energy, solar thermal batteries, exploit photoswitching molecules (solar fuels) that generate heat upon thermal back isomerization. To this date, no molecular approach for solar energy storage and subsequent direct generation of electric current exists because this requires development of light-activatable molecules capable of hysteric electron storage and release. SOLBATT develops molecular systems for transformation of light energy into chemical bonds and their subsequent transformation to electric current. It uses fully organic redox-driven molecular switches that reversibly form an electron storing bond upon redox process and combines them with suitable redox-active partners that facilitate photoinduced electron transfer. SOLBATT (1) improves our understanding of electron storage into chemical bonds and their subsequent release, (2) delivers redox-responsive molecular systems that can be charged or discharged upon external stimulus, and (3) established design principles for photoactive redox materials suitable for the use in organic solar cells. Ultimately, SOLBATT takes the vital step in finding a solution to a challenging issue: combining organic solar cells with electron storage materials for solar electric batteries buffering the inherent fluctuations in solar electricity production.