Quantifying the role of quantum coherence in organic photovoltaic cells

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Eric Bittner of the University of Houston is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry to develop and apply theoretical approaches to study photovoltaic devices. Photovoltaic diodes based on blends of semiconductor polymers and fullerene derivatives now produce power conversion efficiencies exceeding 10% under standard solar illumination. Bittner and his coworkers explore the role of quantum effects in organic polymer-based photovoltaic systems that are of current interest for solar conversion technologies. The proposed work combines accurate quantum chemical methods and a novel search algorithm based loosely upon those used by internet search engines such as Google and Netflix. These methods are used to discover the optimal nuclear motions that facilitate specific quantum transitions in photoexcited molecules. This work will help to reach the goal of a carbon-free economy and reduction of greenhouse gas emissions. Bittner is also developing a theory of entangled photons spectroscopy, a new field with tremendous potential for developing quantum encryption devices. Such devices will be key technological components in future cybersecurity applications.Coherence between quantum mechanical states is an intrinsic and defining component of the transition between two electronic configurations in a molecular system. By quantifying the role of coherence and providing a precise definition of the electron transfer reaction coordinate in a multi-dimensional system, the theoretical methods and analysis produced by this work will give materials scientists and synthetic chemists another means of control of both the rates and pathways for electron and energy transfer events, both of which are triggers for a whole host of important chemical and biological processes. A crucial component of this work will be the development of novel spectroscopic techniques involving entangled photons and quantum optics as probes of chemical dynamics. The Bittner research group is developing a sound theoretical framework connecting photon coincidence counts to molecular-level processes with specific emphasis towards probing collective many-body light-matter excitations. This component of the project will have ramifications in the development of quantum communication and encryption devices?a crucial component in the implementation of the next generation of cybersecurity technologies.