Insight into Controlled Surface Passivation of PEDOT:PSS for Defect Density Modulation and Efficient Charge Transport for Perovskite Solar Cells

Efficient hole transport and low recombination loss at the interfaces of the hole transport layer (HTL)/perovskite layer are vital for a device to attain a high power conversion efficiency (PCE). Here, we demonstrate controlled surface passivation of poly­(3,4-ethylene dioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) by air plasma treatment for various time intervals to reduce defect states present in the HTL/perovskite interfaces. Perovskite grain size improved after the plasma treatment on PEDOT:PSS, decreasing the grain boundary and reducing trap states. The photovoltaic parameters like fill factor (FF) and open-circuit voltage (V oc) were increased after controlled plasma treatment because of reduced trap states at the HTL/perovskite interface resulting in better interfacial connectivity. The plasma treatment on the PEDOT:PSS film increased PCE from ∼14.40% to ∼17.52%. Transient absorption spectroscopy (TAS) was used to monitor charge extraction, transportation, and interface recombination processes. In comparison to the untreated one, the average carrier transport time decreases (520 to 198.7 ps) for PEDOT:PSS films treated for 10 min. Electrical impedance spectroscopy (EIS), transient photovoltage (TPV), and transient photocurrent (TPC) studies correlate charge transport and the recombination process at the PEDOT:PSS/CH3NH3PbI3 interface due to plasma treatment. The defect distribution study provides an in-depth understanding of trap states after plasma treatment.