An ultra-thin chemical vapor deposited polymer interlayer to achieve highly improved stability of perovskite solar cell

Perovskite solar cells (PSCs) have been shining in the photovoltaic industry, but their fragile stability impedes their commercialization seriously. Here we adopt an ultra-thin film of a functional hydrophobic polymer, polychloro-p-dimethyl benzene (Parylene C), which can largely improve the operational lifetime of PSCs as a surface finish. Chemical vapor deposition (CVD) under vacuum is adopted to modify the ultra-thin parylene film, which is thin adequately to afford tunnel contact but is also sufficiently shielding to protect the perovskite layer. Besides, it is demonstrated that the Parylene C film can reduce the perovskite surface defects by interacting with the uncoordinated Pb center and act as an effective hole-hindering barrier in the middle of perovskite and PCBM for decreasing charge recombination. As a result, PSC using a ∼4 nm Parylene C layer exhibits a remarkably increased open-circuit and fill factor and a substantially enhanced efficiency of 21.7 % from pristine 19.4 %. Moreover, the Parylene C-based PSCs have attained long-term thermal and operational stabilities with good reproducibility. Without encapsulation, the degradation was limited to 11 % after 500 h of aging under ambient atmosphere/dark, 85 °C/N2, or constant illumination/ N2 conditions. This work lays a solid foundation for further stability by CVD interface modification.