Enhanced Performance and Stability of Semitransparent Perovskite Solar Cells Using Solution-Processed Thiol-Functionalized Cationic Surfactant as Cathode Buffer Layer

We present a facile and effective method to enhance the performance and stability of perovskite solar cells (PSCs) by the incorporation of solution-processed thiol-functionalized cationic surfactant (11-mercaptoundecyl)­trimethylammonium bromide (MUTAB) as cathode buffer layer (CBL). Our results indicate that the thiol function groups on MUTAB tend to react with the incident Ag atoms to form covalent Ag–S bonds, while no reaction is observed in the case of a methyl-functionalized counterpart dodecyltrimethylammonium bromide (DTAB). Importantly, the presence of Ag–S bonding exerts multipositive effects on the interface, including decrease of contact resistance between the active layer and Ag electrode, improvement of ambient and thermal stability, and reduction of the percolation threshold of ultrathin Ag film. With these desired interfacial properties, the opaque device delivers high power conversion efficiency (PCE) up to 16.5%, which is superior to those of the devices with DTAB (7.9%) and state-of-the-art CBL ZnO nanoparticles (11.0%). The application of MUTAB CBL in semitransparent (ST) solar cells using ultrathin (8 nm) Ag film as transparent top electrode is also demonstrated, and a remarkable PCE of 11.8% with a corresponding average visible transparency (AVT) of 20.8% is achieved, which represents the highest PCE ever reported for ST PSCs with similar AVT. More significantly, the resulting devices possess good ambient stability.