Dual Functional Doping of KMnO₄ in Spiro-OMeTAD for Highly Effective Planar Perovskite Solar Cells

Hole-transport layer (HTL) plays a crucial role in the photovoltaic performance of perovskite solar cells (PSCs). In order to improve the function property of HTLs, we first use potassium permanganate (KMnO4) as a dopant for the oxidization of 2,2′,7,7′-tetrakis(N,N-p-dimethoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD). The reaction between KMnO4 and spiro-OMeTAD produces the oxidized-state spiro-OMeTAD, which enhances the conductivity and adjusts the energy level of HTL. The dual functions of KMnO4 dopant bring high photovoltaic performance of the devices. The planar PSC based on photoactive layer of mixed-cation–anion perovskite and hole-transport layer of spiro-OMeTAD doped with 1.0 mol % KMnO4 achieves a power conversion efficiency of 20.03%. Meanwhile, the hysteresis effect of the device is greatly suppressed. The simple and low-cost processing and significant performance improvement render this method promising.