Grain boundaries act as rapid pathways for nonradiative carrier recombination, anion migration, and water corrosion, leading to low efficiency and poor stability of organometal halide perovskite solar cells (PSCs). In this work, the strategy suppressing the crystal grain boundaries is applied to improve the photovoltaic performance, especially moisture-resistant stability, with polyvinylammonium carbochain backbone covalently connecting the perovskite crystal grains. This cationic polyelectrolyte additive serves as nucleation sites and template for crystal growth of MAPbI3 and afterward the immobilized adjacent crystal grains grow into the continuous compact, pinhole-free perovskite layer. As a result, the unsealed PSC devices, which are fabricated under low-temperature fabrication protocol with a proper content of polymer additive PVAm·HI, currently exhibit the maximum efficiency of 16.3%. Remarkably, these unsealed devices follow an “outside-in” corrosion mechanism and respectively retain 92% and 80% of the initial PCE value after being exposed under ambient environment for 50 days and 100 days, indicating the superiority of carbochain polymer additives in solving the long-term stability problem of PSCs.Keywords: covalently connecting; long-term stability; perovskite solar cell; polyvinylammonium; suppressed boundary;

•GO-hybrided PU/EP IPNs are prepared through an in-situ polymerization.•The friction coefficient is decreased about 30.2% due to GO-hybridization.•The specific wear rate is decreased about two orders of magnitude.•The same friction coefficient in steady stage is obtained independent of GO content.•The identical steady friction coefficients are derived from the same friction bodies.Graphene-oxide-hybrided polyurethane/epoxy interpenetrating polymer networks (PU/EP IPNs) are prepared through an in-situ polymerization. The results showed that the mechanical performance of graphene-oxide-hybrided PU/EP IPNs is improved due to the formation of chemical bonds between graphene oxide nanosheet and polyurethane/epoxy segments, affording the loading transfer from polymer matrix to graphene oxide nanosheet. The average friction coefficient in the steady stage is decreased about 30.2% from neat PU/EP IPN to graphene-oxide-hybrided PU/EP IPNs. Especially, the specific wear rate is decreased about two orders of magnitude from neat PU/EP IPN to graphene-oxide-hybrided PU/EP IPNs. Interestingly, graphene-oxide-hybrided PU/EP IPNs have the same friction coefficient in the steady stage, independent of graphene oxide content. The identical steady friction coefficients are derived from the same friction bodies in three-body friction model, such as graphene-oxide-strengthened PU/EP IPN surface, metallic counterpart and graphene-oxide-wrapping polymer particles as wear debris in the transfer film.