NaCl doped electrochemical PEDOT:PSS layers for inverted perovskite solar cells with enhanced stability

Perovskite solar cells are experiencing an unprecedented growth and might soon replace the conventional solar technologies. For inverted architecture cells, spin coated (SC) PEDOT:PSS has been widely implemented as hole transport material, but it has still unresolved issues regarding stability and scalability. In this work we deposited PEDOT:PSS layers by an alternative electrochemical (EC) route that offers precise synthesis control, scale-up potential and enhanced cell stability. The EC-PEDOT:PSS layers were deposited on ITO substrates from an aqueous solution of EDOT and NaPSS by cyclic voltammetry. Additionally, NaCl in different concentrations was added to the synthesis solution to tune the redox state of the polymer, as confirmed by UV-vis measurements. Photoluminescence emission spectra of MAPbI3 perovskite deposited on EC- and SC-PEDOT:PSS layers showed that both had a similar charge collection efficiency. Furthermore, SEM images demonstrated that MAPbI3 grew similarly on both films. Finally, inverted perovskite solar cells were fabricated using these layers. The results showed that 0.1 M NaCl doped EC-PEDOT:PSS performed similarly as the SC-PEDOT:PSS, achieving efficiencies as high as 11% and improved fill factors exceeding 80%. Most importantly, the EC-PEDOT:PSS significantly improved the stability of the cells, allowing the devices to maintain 90% of their average efficiency after 15 days.