Optimization and simplification of polymer-fullerene solar cells through polymer and active layer design

Polymer-fullerene bulk heterojunction (BHJ) solar cells have consistently been at the forefront of the growing field of organic photovoltaics (OPV). The enduring vision of OPV is the promise of combining a simple, low-cost approach with an efficient, flexible, lightweight platform. While efficiencies have improved remarkably over the last decade through advances in device design, mechanistic understanding, and evolving chemical structural motifs, steps forward have often been tied to a loss of simplicity and a deviation from the central vision of OPV. Within the context of active layer optimization, our focus is to target high efficiency while maintaining simplicity in polymer design and active layer processing. To highlight this strategy, this feature article focuses on our work on random poly(3-hexylthiophene) (P3HT) analogs and their application in binary and ternary blend polymer-fullerene solar cells. These random conjugated polymers are conceptually based on combining simple monomers strategically to influence polymer properties as opposed to the synthesis of highly tailored and synthetically complex monomers. The ternary blend approach further exemplifies the focus on device simplicity by targeting efficiencies that are competitive with complex tandem solar cells, but within the confines of a single active-layer processing step. These research directions are described within the broader context of recent progress in the field of polymer-fullerene BHJ solar cells.