We have studied the effect of lead (II) cyanate Pb(OCN)2 additive on photovoltaic properties of inverted planar solar cells based on inorganic-organic hybrid perovskite CH3NH3PbI3. The active layers of the solar cells were fabricated with a reaction between CH3NH3I and a mixture of PbI2 and Pb(OCN)2. The highest power conversion efficiency was 15%. Hysteresis behaviors in JV curves were reduced. The lifetime of the solar cells was dramatically increased. SEM images indicated that crystallite sizes were enlarged. The OCN groups were not incorporated into crystals from infrared measurements. These results suggest that Pb(OCN)2 affect mainly the crystallization process of CH3NH3PbI3.