2D Conjugated Polyelectrolytes Possessing Identical Backbone with Active-Layer Polymer as Cathode Interlayer for Organic Solar Cells

Abstract

A 2D conjugated polyelectrolyte (CPE), PBDTTh-TT-NBr, having the same backbone as the highly efficient donor polymer PTB7-Th and the quaternary ammonium pendant, is synthesized as a cathode interlayer (CIL) material for PTB7-Th-based fullerene and non-fullerene solar cells. The quaternary ammonium group is connected to the 2D conjugated backbone by a long, flexible alkyl chain, facilitating the modification of cathode via forming interface dipoles. Moreover, compared with another CPE analogue to PTB7, PBDT-TT-NBr, without the 2D conjugated backbone, the PBDTTh-TT-NBr presents a higher similarity in polymer structure to the donor polymer PTB7-Th. This feature makes it more compatible with the PTB7-Th-based active-layer film, improving the electron transport. With the PBDTTh-TT-NBr as the CIL, devices afford higher performances than those using the PBDT-TT-NBr in both fullerene and non-fullerene systems. This work offers guidance on choosing the CIL material that ought to possess a highly similar structure to the active-layer component.

Keywords: 2D conjugated polyelectrolytes; cathode interface layers; polymer solar cells; structural similarity.