Herein, a facile one step hydrothermal route for the controlled, biomass assisted synthesis of three dimensional (3D) Zinc oxide (ZnO) hierarchical superstructures (HSs), assembled with compacted ZnO nanorods (NRs) is reported. Anionic polysaccharide "Polygalacturonic acid" is utilized as a crystal growth modifier for assembling the basic building blocks (ZnO NRs). Probable mechanism for the formation of superstructures through the interaction between the polysaccharide and ZnO growth units is discussed. Photovoltaic properties of as-synthesized 3D ZnO HSs as compared to its basic structural unit i.e., ZnO NRs are investigated by sensitizing with a bisthiazole linked metal free donor-acceptor dye; D1. A substantial enhancement (similar to 35%) in efficiency (eta) for 3D ZnO HSs based device (eta approximate to 5.37%) as compare to ZnO NRs (eta approximate to 3.48%) is being observed, mainly due to better charge separation and collection, owing to a superior electron transport ability of compacted building blocks, better light-scattering effect, higher BET surface area for sensitizer loading and efficient electron injection from dye D1 to the ZnO. Electrochemical impedance spectroscopic (EIS) analysis is carried out to support a slower photogenerated electron-hole recombination rate and better charge transports in the 3D ZnO HSs based photovoltaic device. (c) 2017 Elsevier Ltd. All rights reserved.