The production of hydrogen from water via solar energy conversion has attracted immense attention as a potential solution for addressing energy supply issues. We demonstrated a stable and efficient organic inorganic hybrid photoelectrochemical (H-PEC) cell. Modifying the surface energy and structure of the organic photoactive layer using multi-functional nanomaterials including -OH-modified NiO nano particles and reduced graphene oxide (RGO) led to a 2.8-fold enhancement of the water splitting performance in a single junction H-PEC cell. The enhanced performance was attributed to the i) improved water-wettability, ii) enhanced charge extraction property by band-edge alignment, and iii) the catalytic effect of the introduced NiO-OH nanoparticles. In addition, because of the effects of the RGO layer preventing water penetration and photo-corrosion during the oxidation of water, a distinguishable longterm stability was achieved from the H-PEC cell with an RGO capping layer. The best performance was obtained from the organic-inorganic hybrid multi-junction PEC cells consisting of the WO3 photo-anode (activated under UV irradiation) and the H-PEC cell (activated under visible light irradiation). The H-PEC cell with a WO3 photo-anode exhibited significantly enhanced stability and performance by a factor of 11.6 higher than photocurrent of the single H-PEC cell. (C) 2016 Elsevier B.V. All rights reserved.