Untangling the essence of bulk heterostructure organic solar cells: Why complex need not be complicated

The A new class of Macroelectronic devices appropriate for large area flexible electronics, supercapacitors, batteries, and solar cells rely on the biological dictum that ‘form defines function’ and use structural geometry to compensate for the poor intrinsic transport in materials processed at low temperature [1]. Bulk heterostructure solar cells with two intermixed polymers acting as the acceptor/donor layers provide a striking example of such biomimetic design. The optimization of this class of devices has long been stymied by a lack of theoretical tools and transport models that can treat the geometry of structure at par with transport characteristics and that does not resort to classical transport theories originally developed for spatially homogenous media. In this presentation, I will use theories of spinodal decomposition, geometric transform, and percolation models to demonstrate how simple ideas can untangle the complex (transport) geometry of BH solar cells [2–5]. Indeed, the essence of the most important aspects of organic solar cells like short circuit current [2–4], open circuit voltage [2], fill-factor, reliability [5], etc. can be described by no more than a few lines of algebra. Our approach allows an intuitive understanding of the essential features of performance and reliability of BH solar cells and establish the fundamental principle of optimization and trade-off that must dictate the design of such devices.