Two organolead halide perovskite nanocrystals, CH3NH3PbBr3 and CH(3)NH(3)Pbl(3), were found to efficiently sensitize TiO2 for visible-light conversion in photoetectrochemical cells. When self-assembled on mesoporous TiO2 films, the nanocrystattine perovskites exhibit strong band-gap absorptions as semiconductors. The CH(3)NH(3)Pbl(3)-based photocell with spectral sensitivity of up to 800 nm yielded a solar energy conversion efficiency of 3.8%. The CH3NH3PbBr3-based cell showed a high photovoltage of 0.96 V with an external quantum conversion efficiency of 65%.