The essence and efficiency limits of bulk-heterostructure organic solar cells: A polymer-to-panel perspective

Bulk-heterojunction organic photovoltaic (BHJ-OPV) technology promises high efficiency at ultralow cost and weight, with potential for nontraditional applications such as building-integrated photovoltaic (PV). There is a widespread presumption that the complexity of morphology makes carrier transport in OPV irreducibly complicated and, possibly, beyond predictive modeling. However, understanding the complex morphology is important because it not only dictates cell efficiency but also the panel performance and the operating lifetime. In this paper, we derive the fundamental thermodynamic as well as morphology-specific practical limits of BHJ-OPV efficiency and lifetime. We find that performance improvement relies not only on morphology engineering but also on increasing the effective mobility-lifetime (mu tau) product, the cross-gap between donor/acceptors, and reducing the series resistance. Even if the OPV fails to achieve the highest efficiency anticipated by the thermodynamic limit, its novel form factor, lightweight, and transparency can make it a commercially viable option for many applications.