This work focuses on reducing the hysteresis and improving the stability of TiO2-based perovskite solar cells. A simple slow hydrolysis and rapid evaporation (SHRE) method was developed to deposit amorphous nanoporous WOx up on the TiO2 base at low temperature to form a TiO2-WOx bilayer as composite electron transport materials (ETMs) for efficient CH3NH3PbI3 solar cells. In the composite bilayers, the nanoporous WOx sublayer functions as an effective scaffold to modify the electrical contact between the perovskite and TiO2, and also as an anti-reflective film to enhance light transmittance. The WOx modifying layer much reduces the serious hysteresis and the dependence of power conversion efficiencies (PCEs) on the J-V scan rates. Moreover, it has also significantly enhanced the long-term stability of solar cells. The functioning mechanism for the WOx modifying layer in the TiO2-WOx composite ETMs is explored and interpreted in terms of nanoporous inorganic scaffolds and also the salutary effect of capacitive currents from the high-capacitance WOx.