Synthesis of nickel sulfides of different phases for counter electrodes in dye-sensitized solar cells by a solvothermal method with different solvents

Two phases of nickel sulfide (alpha-NiS and beta-NiS) nanoarchitectures were successfully and controllably synthesized by a facile solvothermal method with two different solvents of alcohol and water, respectively. The products were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV-vis diffuse reflectance spectrophotometer. The sphere-like shape for alpha-NiS and cross-like shape composed of nanorods for beta-NiS are uniform and well distributed as well as their size. Both alpha-NiS and beta-NiS powders were used as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). It is found that the DSSC with an alpha-NiS CE performs much better than the one with a beta-NiS CE. The energy conversion efficiency of the former was 5.2%, whereas the latter was 4.2%, about 20% increment.