Nonpolar Solvent-Dispersible Alkylated Reduced Graphene Oxide for Hole Transport Material in n-i-p Perovskite Solar Cells

Abstract

Reduced graphene oxides (rGOs), despite their excellent electrical properties, have been seldom used as the solution-processed sole hole transport material (HTM) in perovskite solar cells (PeSCs) with an n-i-p structure, due to their low dispersity in orthogonal solvent of perovskite, such as chlorobenzene (CB). The limited rGO dispersion in nonpolar solvents precludes the formation of a fully covered film on top of the perovskite layer. A newly designed alkylated rGO (AF-rGO) is synthesized, which can be highly dispersed in a nonpolar solvent, for use as a solution-processed HTM on top of the perovskite layer in PeSCs. The AF-rGO can be dispersed in CB at a high concentration, and a fully covered AF-rGO film is successfully introduced on top of the perovskite layer as HTM through a simple solution process. The AF-rGO in the PeSC exhibits minimal series resistance and charge recombination and exhibits efficient hole extraction and transport abilities, resulting in a maximum power conversion efficiency (PCE) of 17%, which is the highest PCE of PeSCs with an n-i-p structure, which use graphene-based materials as the sole HTM. Moreover, devices with AF-rGO HTM exhibit improved ambient stability, exhibiting 89% of their original performance after 240 h of storage without encapsulation.