Ternary complex oxides with cubic pyrochlore structure BixFeyWOq (BFWO) were obtained by hydrothermal synthesis at different pH values of hydrothermal fluid and were first used as electron transport layers in perovskite solar  cells (PSCs). The analysis of photovoltaic parameters measured for BFWO-based PSCs demonstrated that BFWO materials obtained at pH 2 allow improving the PSC performance by ~ 4% (rel.) in comparison with state-of-the-art PSCs. In addition, BFWO-based PSCs exhibited higher tolerance to the degradation under continuous illumination.