Investigating the role of reduced graphene oxide as a universal additive in planar perovskite solar cells

In this work we present the effects of the incorporation of reduced graphene oxide (rGO) nanoflakes into the titania compact layer, the methylammonium lead iodide (CH3NH3PbI3) absorber and the Spiro-MeOTAD hole transporter which are typical components of a planar perovskite solar cell (PSC). The addition of rGO within the TiO2 electron transport layer (ETL) offers fast electron transport rates toward the anode and favors the growth of large, uniform perovskite crystals. When added in MAPbI(3), rGO further increases the perovskite grains size and creates a more homogenous and smooth film with enhanced crystallinity, thus improving the power conversion efficiency (PCE) of the corresponding PSC. On the contrary, its presence in Spiro-MeOTAD is detrimental for the cells performance. For the first time in the literature a graphene derivative favors the performance of a MAPbI(3)-based PSC when incorporated as an additive in both the ETL and the perovskite absorber. As a result, we obtained devices with optimized electrical characteristics, resulting to stabilized 13.6% PCE, outperforming by 20% the reference (rGO-free) ones. Moreover, the presence of rGO offered additional stability to the solar cells which retained 40% of their initial PCE after 50 days of storage in mildly humid, dark environment.