Charge Accumulation, Recombination, and Their Associated Time Scale in Efficient (GUA)(x)(MA)(1–x)PbI(3)-Based Perovskite Solar Cells

[Image: see text] Here, we study the influence of guanidinium (GUA) ions on the open-circuit voltage (V(oc)) in the (GUA)(x)(MA)(1–x)PbI(3) based perovskite solar cells. We demonstrate that incorporation of GUA forms electronic and ionic accumulation regions at the interface of the electron transporting layer and perovskite absorber layer. Our electrochemical impedance spectroscopy results prove that the formed accumulation region is associated with the enhanced surface charge capacitance and photovoltage. Furthermore, we also demonstrate the influence of the GUA ions on the enhanced interfacial and bulk electronic properties due to more efficient charge transfer between the bulk and interfaces and the reduced electronic defect energy levels.