Zinc oxide (ZnO) as an electron transport material has been used in regular planar perovskite solar cells (PSCs). Herein, ZnO nanoparticles serve as an additive directly in perovskite active layer in order to fabricate a bulkheterojunction inverted planar PSC. The CH3NH3PbI3-xClx:ZnO bulk heterojunction is prepared by mixing ZnO nanoparticles into CH3NH3PbI3-xClx precursor solution. ZnO nanoparticles act as catalytic centers and induce the growth of perovskite grains leading to the formation of large-size perovskite crystals. Remarkably, hysterysis-free power conversion efficiency of 17.26% is achieved when precisely control the concentration of ZnO nanoparticles in CH3NH3PbIxCl3-x:ZnO bulk heterojunction active layer. The presence of ZnO nanoparticles in the perovskite films enhances the conductivity and electron mobility. Efficient charge injection of CH3NH3PbIxCl3-x:ZnO film can improve charge extraction in the PSCs. Moreover, the PSCs with CH3NH3PbIxCl3-x:ZnO bulk heterojunction exhibit high fill factor of 77.3% and short current density of 22.71 mA cm(-2), which is attributed to improved perovskite quality. The bulk heterojunction structure is fabricated by combining perovskite and metal oxides, which is of great importance to the development and commercialization of PSCs in the future.