Potassium thiocyanate additive for PEDOT:PSS layer to fabricate efficient tin-based perovskite solar cells

Although the commercialized poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) is usually used as hole transport layer (HTL) in tin-based perovskite solar cells (TPSCs), its acidity damage the stability of TPSCs and restrict its further development. The PEDOT:PSS solution can be diluted by water to decrease acidity and reduce the cost of device fabrication, but the electrical conductivity will decrease obviously in diluted PEDOT:PSS. Herein, potassium thiocyanate (KSCN) is selected to regulate the properties of PEDOT:PSS HTL from the diluted PEDOT:PSS aqueous solution by water with a volume ratio of 1:1 to prepare efficient TPSCs. The concentrations of KSCN additive have been optimized. The effects of KSCN addition on the structure and photoelectrical properties of PEDOT:PSS HTL and TPSCs have been systematically studied. At the optimal KSCN concentration, the TPSCs based on KSCN-doped PEDOT:PSS HTL (KSCN-PSCs) demonstrate a champion power conversion efficiency (PCE) of 8.39%, while the reference TPSCs only show a champioan PCE of 6.70%. A series of characterization demonstrate that the KSCN additive increases the electrical conductivity of HTL prepared by the diluted PEDOT:PSS solution, improves the microstructure of perovskite film and inhibit carrier recombination in TPSCs, leading to the reduced hysteresis effect and enhanced PCE in KSCN-PSCs. This work gives a low-cost and practical strategy to develop a high-quality PEDOT:PSS HTL from diluted PEDOT:PSS aqueous solution for efficient TPSCs.