In Situ Solution-Processed Submicron Thick SiO_xC_y/a-SiN_x(O):H Composite Barrier Film for Polymer:Non-Fullerene Photovoltaics

Aiming to improve the environmental stability of organic photovoltaics, a multilayered SiOxCy/a-SiNx(O):H composite barrier film coated with a hydrophobic perfluoro copolymer stop layer for polymer:non-fullerene solar cells is developed. The composite film is prepared by spin-coating of polysilicone and perhydropolysilazane (PHPS) following a densification process by vacuum ultraviolet irradiation in an inert atmosphere. The transformation of polysilicone and PHPS to SiOxCy and a-SiNx(O):H is confirmed by Fourier transform infrared and energy-dispersive X-ray spectroscopy measurement. However, the as-prepared PHPS-derived silicon nitride (PDSN) can react with moisture in the ambient atmosphere, yielding microscale defects and a consequent poor barrier performance. Treating the incomplete PDSN with methanol vapor significantly densifies the film yielding low water vapor transmission rates (WVTRs)of 5.0 x 10(-1) and 2.0 x 10(-1) g m(-2) d(-1) for the one- and three-couple of SiOxCy/a-SiNx(O):H (CON) composite films, respectively. By incorporating a thin hydrophobic perfluoro copolymer layer, the three-coupled methanol-treated CON film with a total thickness of 600 nm shows an extremely low WVTR of 8.7 x 10(-4) g m(-2) d(-1). No performance decay is measured for the PM6:Y6 and PM6:L8-BO cells after such an encapsulation process. These encapsulated polymer cells show good stability storaged at 25 degrees C/50% relative humidity, or under simulated extreme rainstorm tests.