Enhancement of efficiency and stability in organic solar cells by employing MoS2 transport layer, graphene electrode, and graphene quantum dots-added active layer

Abstract

For enhancing efficiency and flexibility of organic solar cells, new constituent materials are highly required. Here, we first report flexible organic solar cells (FOSCs) by employing MoS2 hole transport layer (HTL), bis(trifluoromethanesulfonyl)-amide-doped graphene (TFSA-GR) transparent conductive electrode (TCE), and GR quantum dots (GQDs)-added active layer. Power conversion efficiency (PCE) of the FOSCs without GQDs strongly depends on number of layers (Ln) of MoS2 as well as on doping concentration (nD) of TFSA-GR, thereby showing maximum PCE of 3.56% at Ln = 2 and nD = 20 mM, resulting from the lowest resistance at the TCE/MoS2/active layer interfaces. The long-term stability of the FOSCs is almost two times better than that of their counterparts with conventional organic HTL. By adding GQDs in the active layer, the PCE is further enhanced to 4.23% and is maintained at 89/82% of the original value after inner/outer repeated bending tests for 1000 cycles, respectively, indicating outstanding mechanical stability. These results suggest that GQDs are very useful for the active layer of FOSCs with better PCE and flexibility.