Growth of 2D passivation layer in FAPbI3 perovskite solar cells for high open-circuit voltage.

• Cyclopropylcarbamidine hydrochloride is applied onto the surface of FAPbI 3 perovskite film for defects passivation. • With optimized energy levels, a peak PCE of 22.8% with an optimal voltage loss of 0.34 eV is achieved. • The hydrophobicity of the 2D passivation layer contributes to the enhancement of device stability. [Display omitted] Here, we demonstrate cyclopropylcarbamidine hydrochloride (CPAH) as a novel organic halide salt to construct 2D layer for surface passivation of phase-pure FAPbI 3 film. The results verify that the introduction of 2D passivation layer is beneficial to the suppression of charge recombination and the promotion of charge transfer. With prolonged charge carrier lifetime and optimized energy levels, an impressive PCE of 22.8% is obtained for the as-prepared planar devices based on 3D FAPbI 3 /2D (CPA) 2 PbI 2 Cl 2 , along with simultaneous enhancement of open circuit voltage and fill factor. The optimal voltage loss is controlled to be 0.34 eV. What's more, the 2D layer-containing unencapsulated devices show significantly enhanced wet-, thermal- and light stability. Our findings further pave the way of utilizing novel organic halide salts for 2D perovskite construction, which provides a deeply investigated route for the fabrication of efficient and stable perovskite solar cells. [ABSTRACT FROM AUTHOR]