The solvent treatment effect of the PEDOT:PSS anode interlayer in inverted planar perovskite solar cells

Inverted planar perovskite (PVSK) solar cells with a device structure of ITO/PEDOT:PSS/PVSK/PC61BM/Al have emerged as a new generation solar cell owing to their advantages of high power conversion efficiency (PCE), low processing temperature and potential low cost. In this paper, the polar solvent treatment effect of the PEDOT:PSS anode interlayer on PVSK solar cell performance was investigated. The conductivity of the PEDOT:PSS film was found to increase by washing with polar solvents, including H2O, ethanol (EtOH), and a mixture solvent of ethanol and H2O (EtOH : H2O = 8 : 2 v/v), which was attributed to the removal of the PSS component from the PEDOT:PSS film, leading to a PEDOT-rich surface. However, the PCE of perovskite solar cells decreased from 9.39% for the pristine PEDOT:PSS film based device to 4.21%, 8.35%, 7.13% for the H2O-, EtOH- and EtOH : H2O-treated PEDOT:PSS film based devices, respectively, suggesting that the high conductivity of the PEDOT:PSS film does not ensure a high device performance of the inverted PVSK solar cells. UV-Vis absorption spectra, AFM surface morphology and SEM images of the PVSK films deposited on different PEDOT:PSS surfaces were studied, and the results showed that PEDOT-rich surface is not favorable for the crystal growth of PVSK layer, and consequently leads to poor device performances. This conclusion was further supported by the improved device performance of PVSK solar cells based on a PEDOT:PSS/PSSNa anode buffer layer, where an additional poly(sodium p-styrenesulfonate) (PSSNa) layer was deposited on the PEOT:PSS surface.