Upright-standing nanoporous nanosheets of iodine-doped ZnO (ZnO:I nanocrsytallites were grown hydrothermally at low temperature and studied as dyesensitized solar-cell electrodes. The highest overall energy-conversion efficiency of,similar to 6.6% was achieved with the film consisted of nanosheets of ZnO:I nanocrystallites. This efficiency was significantly improved than the 3.2% achieved for ZnO:I films only including nanosized crystallites, and higher than the 2.4% for undoped ZnO nanosheet film. The nanosheets of ZnO:I nanocrsytallites were proven to be positive in causing light scattering in a broad wavelength region and, therefore, enhancing the light harvesting capability of the photoelectrode film and thus, promotes the solar cell performance. The fabricated cells exhibited highly durable cell performances, even after a month under atmospheric conditions. Electrochemical impedance spectroscopy (EIS) data confirmed that iodine doping was helpful to lower the recombination resistance and prolonged electron lifetime of the ZnO:I cells, hence diminishing the recombination process. The efficiency achieved for the best DSSC in this work was much better than ever reported for a ZnO-based DSSC.