In Situ Solution‐Processed Submicron Thick SiOxCy/a‐SiNx(O):H Composite Barrier Film for Polymer:Non‐Fullerene Photovoltaics

Abstract Aiming to improve the environmental stability of organic photovoltaics, a multilayered SiO x C y /a‐SiN x (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 SiO x C y and a‐SiN x (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 × 10 −1 and 2.0 × 10 −1 g m −2 d −1 for the one‐ and three‐couple of SiO x C y /a‐SiN x (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 × 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 °C/50% relative humidity, or under simulated extreme rainstorm tests.