Amino acid-induced morphogenesis of ZnO nanocrystallite aggregates for efficiency enhancement in dye-sensitized solar cells

A novel complex of ZnO nanocrystallite aggregates with superior light-scattering capability was synthesized via an eco-friendly aqueous solution method and investigated as a photoanode material for dye-sensitized solar cells (DSSCs). The nanocrystallite aggregate complex was produced by adding a suitable amount of glutamic acid into the reaction mixture as a shape modulating agent. In the absence of glutamic acid, only flower-shaped nanocrystallite aggregates, or nanoflowers, approximately 400-500 nm in dimension were obtained. In the presence of glutamic acid, irregularly shaped aggregates that were loosely packed and relatively small in size formed around the flower-shaped aggregates. Both the flower-like and the irregularly shaped aggregates were composed of nanocrystals approximately 30-50 nm in size. Thus prepared nanocrystallite aggregates were constructed into DSSC photoanode films using a low-temperature (150 °C) thermal treatment process. When paired with the organic dye D149, the complex-based DSSCs achieved a power conversion efficiency of 5.07%, 26% higher than the 4.02% efficiency attained by the nanoflower-based ones. The reference DSSCs made of commercial nanoparticles only reached a power conversion efficiency of 3.64%. The improvement in photovoltaic performance by the complex-based cells may be attributed to their enhanced light harvesting efficiency as a result of superior light-scattering ability and possibly higher dye loading of the complex-based photoanode.