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[Display omitted] • Observed the phase transition of perovskite driven by SnO 2 under UV light. • In-situ synthesis of PSS-Pb layer at the interface of SnO 2 /perovskite. • The PSS-Pb layer was used as barrier to inhibit phase-transition of perovskite. • The PSS-Pb layer stabilize the interface and passivate interface defects. • Obtained a high open-circuit voltage of 1.19 V and an improved efficiency of 22.26% The harmonious coordination between the perovskite and the charge transport layer is the prerequisite for the high efficiency and stability of perovskite solar cells (PSCs). The excellent photoelectric and solution processable SnO 2 electron transport material opens the most commercial potential of planar PSCs. However, SnO 2 has rich surface activity and photocatalytic properties, which will deteriorate perovskite after absorbing UV light and seriously affect the stability and efficiency of PSCs. Here, the interface barrier strategy is introduced to insert an anchored-then-rinsed lead polystyrene sulfonate (ARPSS-Pb) polyionic layer between SnO 2 and perovskite via in-situ synthesis method to construct a new stable interface, which can effectively block the phase transition of perovskite driven by photocatalytic SnO 2. In addition, ARPSS-Pb also has the functions of passivating interfacial defects, relaxing interfacial stress and guiding crystallization of perovskite. PSCs based on ARPSS-Pb achieved a power conversion efficiency (PCE) of 22.26%, much higher than 19.60% of the control devices. More importantly, after 1000 h of storage under continuous humidity conditions, up to 96.32% of the initial PCE is maintained. A high open circuit voltage (V OC) as high as 1.190 V has been obtained for ARPSS-Pb based devices. To our best knowledge, this is the highest V OC achieved in the system of perovskite with 1.56 eV energy gap. [ABSTRACT FROM AUTHOR]