Mesoporous nanocrystalline ZnO applied to a-Si/mesoporous tandem solar cell was synthesized through the hydrothermal method. The structures and morphologies were characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Brunauer-Emmett-Teller (BET) analysis based on the nitrogen adsorption isotherm. The test results indicated that the samples had an average pore size of 17 nm and the BET specific surface area was approximately 37.5 m2/g. The transparent a-Si film on fluorine-tin-oxide (FTO) coated glass was obtained by chemical treatment and was used to structure a-Si/mesoporous ZnO tandem solar cell. Under AM 1.5 irradiation, the a- Si/mesoporous tandem solar cell had an open circuit voltage (Voc) of 560 mV, a short circuit current (Jsc) of 3.61 mA/cm2 and a conversion efficiency of 0.28%. The conversion efficiency of tandem solar cell was improved obviously than that of the transparent a-Si film, which had lost special solar cell properties in chemical processing.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.