Tuning the work functions of graphene quantum dot-modified electrodes for polymer solar cell applications

Abstract

The graphene quantum dot (GQD) is a new kind of anode/cathode interlayer material for polymer solar cells (PSCs). The key requirement for a cathode interlayer (CIL) is a low work function. In this article, aiming at application as a CIL for PSCs, we report a general approach to tune the work function of GQD-modified electrodes using alkali metal cations, e.g. Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺. For ITO electrodes modified with these GQDs containing alkali metal cations, the work function can be finely tuned within the range of 4.0–4.5 eV. Owing to their low work function, GQDs containing K⁺, Rb⁺ and Cs⁺ can be used as CILs for PSCs. Their device performance is fairly comparable to that of the state-of-the-art CIL material ZnO. This work provides a rational approach to tune the properties of GQD and to design solution-processable electrode interlayer materials for organic electronic devices.