Semiconductor hierarchically structured flower-like clusters for dye-sensitized solar cells with nearly 100% charge collection efficiency

By combining the ease of producing ZnO nanoflowers with the advantageous chemical stability of TiO 2 , hierarchically structured hollow TiO 2 flower-like clusters were yielded via chemical bath deposition (CBD) of ZnO nanoflowers, followed by their conversion into TiO 2 flower-like clusters in the presence of TiO 2 precursors. The effects of ZnO precursor concentration, precursor amount, and reaction time on the formation of ZnO nanoflowers were systematically explored. Dye-sensitized solar cells fabricated by utilizing these hierarchically structured ZnO and TiO 2 flower clusters exhibited a power conversion efficiency of 1.16% and 2.73%, respectively, under 100 mW cm −2 illumination. The intensity modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) studies suggested that flower-like structures had a fast electron transit time and their charge collection efficiency was nearly 100%. The IMPS/IMVS measurement indicated that the transit time of TiO 2 flower-cluster DSSCs was only 1/4 of that of nanoparticle DSSCs under 100 mW cm -2 illumination. The charge collection efficiency of TiO 2 flower-cluster DSSCs reached 96%.