Quaternisation-polymerized N-type polyelectrolytes: synthesis, characterisation and application in high-performance polymer solar cells

Perylene diimide (PDI) based semiconductors with high mobility are promising electron-transporting materials (ETMs), which are used to fabricate polymer solar cells (PSCs) using roll-to-roll (R2R) processing. However, PDI-based molecular semiconductors have a strong tendency to aggregate, which hinders their use as ETMs in the fabrication of high-performance thin-film devices. Additionally, multi-layer organic opto-electronic devices require that the materials for different layers should possess orthogonal solubility. Here, we develop an in situ polymerisation method to successfully prepare ion-containing PDI-based polyelectrolytes with good water/alcohol solubility, which can enable high-performance PSCs. The doping behaviour, self-assembling and charge-transporting properties of these polyelectrolytes can be fine-tuned by their anions, which allows the fabrication of high-quality and high-mobility electron-transporting thin films for PSCs. PSCs with these polyelectrolytes can maintain high power conversion efficiencies of over 8% when the thickness of the polyelectrolyte is up to 50 nm, which offers a remarkable processing window for the mass-fabrication of PSCs using R2R techniques. Our findings on the structure-property-performance relationships of these polyelectrolytes provide insights and guidelines for the design of high-performance n-type polyelectrolytes for organic opto-electronic devices.