Iodide-reduced graphene oxide with dopant-free spiro-OMeTAD for ambient stable and high-efficiency perovskite solar cells†
Hygroscopic lithium-bis(trifluoromethane)sulfonimide (Li-TFSI) and corrosive pyridine doped 2,2′,7,7′-tetrakis(N,N-di-p-methoxy-phenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) in perovskite solar cells generally results in poor device ambient stability due to moisture-induced degradation of the perovskite absorber. Simultaneously fulfilling good ambient stability and high efficiency, this work proposes the use of a p-type and highly conductive reduced graphene oxide (RGO) reduced by ferrous iodide acid solution, combined with dopant-free spiro-OMeTAD as a hole extraction and transport material in perovskite solar cells, achieving a maximum power conversion efficiency (PCE) of 10.6%, greatly outperforming the reference devices based on pure dopant-free spiro-OMeTAD (PCE = 6.5%). Impressively, only a 15% PCE degradation is observed for the device with RGO/dopant-free spiro-OMeTAD without encapsulation after 500 h, whereas the PCE drops by 65% for the device with Li-TFSI and pyridine doped spiro-OMeTAD. This work represents a significant step toward the realization of stable and high-efficiency perovskite solar cells.