High-Molecular-Weight Regular Alternating Diketopyrrolopyrrole-based Terpolymers for Efficient Organic Solar Cells

摘要

The recent significant increase in power conversion efficiency (PCE) of polymer-fullerene solar cells largely originates from the successful development of new electron donor polymers. The donor-acceptor (D-A) or push-pull design, where electron-rich and electron-deficient units alternate along the copolymer chain- is commonly used to tune the HOMO and LUMO energy levels and the optical band gap of these polymers. While structure-property relationships for energy levels are well-established, these are less clear for the actual photovoltaic performance. Creating morphologies in which nanometer-sized, interconnected, semi-crystalline domains of both polymer and fullerene exist seems crucial for high photovoltaic performance. These semi-crystalline domains optimize the conjugation along the polymer backbone and allow delocalizing the carrier wave functions to assist efficient charge separation. A high molecular weight and a tendency to crystallize are important in achieving such morphologies.