Kalium persulfate as a low-cost and effective dopant for spiro-OMeTAD in high performance and stable planar perovskite solar cells

Abstract Hole transport materials (HTMs) play an important role for achieving high performance and stable perovskite solar cells (PSCs). Although the state-of-the-art HTM, spiro-OMeTAD, has been successfully applied in PSCs, it exhibits an inferior conductivity and hole mobility, which hampers its future application in commercial PSCs. In this study, a common and strong inorganic oxidant, kalium persulfate (KPS), is introduced as a p-type dopant into spiro-OMeTAD for PSCs with a regular n-i-p architecture. By the introduction of KPS into spiro-OMeTAD films, we systematically investigated the morphology, optoelectrical properties and energy level of KPS-doped hole transport layer (HTL). The results indicate that the incorporation of KPS could not only oxidize spiro-OMeTAD efficiently, but also suppress ion migration by passivating the defect states at the perovskite surface. Accordingly, the KPS-modified PSC with a champion PCE of 20.23% delivered a stabilized output efficiency of 19.59%, while the control device exhibited an inferior PCE of 18.29% with a stabilized power output of 17.51%. More importantly, the devices employed KPS-doped spiro-OMeTAD exhibited less hysteresis and superior long-term stability. Our study provides an insight for HTL engineering by using a low-cost inorganic oxidant for highly efficient and stable PSCs.