Graphene scaffolds enhanced photogenerated electron transport in ZnO photoanodes for high-efficiency dye-sensitized solar cells

Graphene and ZnO as two star materials were united to constitute the photoanode of dye-sensitized solar cells (DSSCs). Highly electronically conductive graphene scaffolds incorporated into ZnO hierarchically structured nanoparticle (HSN) photoanodes could simultaneously capture and transport photogenerated electrons injected into ZnO by excited dyes. This strategy was beneficial for electrons to fluently transfer to the collection electrode due to the decreased internal resistance and electron recombination loss. On the basis of these advantages, the DSSC incorporating 1.2 wt % graphene into the ZnO photoanode with 3 μm in thickness exhibited a high short-circuit photocurrent density (J_sc) of 10.89 mA/cm² and a power conversion efficiency (PCE) of 3.19%, which were increased by 43.48% and 38.09%, respectively, compared with those of the DSSC without graphene. It was found that the incorporated graphene could markedly prolong electron lifetime (τ_eff) and effective diffusion length (L_n), which allowed the utilization of thicker photoanodes that could afford enhanced surface area for higher dye loading and light harvesting. Thus, an impressively high PCE of 5.86% was achieved for the DSSC composed of 9-μm-thick ZnO photoanode, which could be the highest PCE compared with previous reports with the same thick photoanodes. These results demonstrate potential application of graphene for improving the performance of DSSCs.