Graphene oxide/PEDOT:PSS composite hole transport layer for efficient and stable planar heterojunction perovskite solar cells

We investigated a graphene oxide (GO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) composite as a promising candidate for the practical application of a 2-D carbonaceous hole transport layer (HTL) to planar heterojunction perovskite solar cells (PeSCs) consisting of a transparent electrode/HTL/perovskite/fullerene/metal electrode. Both the insulating properties of GO and the non-uniform coating of the transparent electrode with GO cause the poor morphology of perovskite induced low power conversion efficiency (PCE) of 6.4%. On the other hand, PeSCs with a GO/PEDOT:PSS composite HTL, exhibited a higher PCE of 9.7% than that of a device fabricated with conventional PEDOT:PSS showing a PCE of 8.2%. The higher performance is attributed to the decreased series resistance (R_S) and increased shunt resistance (R_Sh). The well-matched work-function between GO (4.9 eV) and PEDOT:PSS (5.1 eV) probably results in more efficient charge transport and an overall decrease in R_S. The existence of GO with a large bandgap of ∼3.6 eV might induce the effective blocking of electrons, leading to an increase of R_Sh. Moreover, improvement in the long-term stability under atmospheric conditions was observed.