Compact hybrid cell based on a convoluted nanowire structure for harvesting solar and mechanical energy.

IO N The harvesting of energy from the environment dates back to the age of the windmill and the waterwheel. Their modern counterparts are hydro-power plants, wind farms, solar farms, and more recently, novel piezoelectric devices [ 1 ] for power generation from mechanical vibration. [ 2 ] Fully utilizing power sources such as light, [ 3–5 ] thermal, and mechanical energy is of great importance to our long-term energy needs [ 6 ] and sustainable development [ 7 ] At a small scale, the development of a wireless self-powered system [ 8 ] that harvests its operating energy from the environment is of great importance and an attractive proposition for sensing, [ 9 ] personal electronic, [ 10 ] and defense technologies. Recently, harvesting multiple type energy using a single device has been a new trend in energy technologies. The fi rst multimode energy harvester [ 11 ] has been demonstrated for simultaneously harvesting solar and mechanical energy. Recently, the hybrid cell has been developed for concurrently harvesting biochemical and mechanical energy for in vivo applications. [ 12 , 13 ] This multimode energy harvester has the potential of fully utilizing the energy in the environment under which the devices will be operating. The prototype of the nanowire-based hybrid cell demonstrated to harvest both solar and mechanical energy is using a dye-sensitized solar cell (DSSC) [ 14 , 15 ] and piezoelectric nanogenerator. [ 16 ] However, due to the encapsulation problem posed by the use of the liquid electrolyte [ 17 ] in conventional DSSCs, solvent leakage and evaporation are two major obstacles, thus the present hybrid cell is actually a back-to-back physical integration of a nanogenerator and a DSSC on the same substrate, which may limit its performance. We report here an innovative approach that convolutes a solid-state dye-sensitized solar cell [ 18 ] and an ultrasonic wave driven piezoelectric nanogenerator into a single compact structure for concurrently harvesting solar and mechanical energy. The structure is fabricated based on vertical ZnO nanowire arrays [ 19 ] with the introduction of solid electrolyte and metal coating. Under light illumination of a simulated sun emission (100 mW/cm 2 ), the optimum power is enhanced by 6% after incorporating the contribution of the nanogenerator. This research provides a platform towards multimode energy harvesting as practical power sources. The design of the compact hybrid cell (CHC) was to convolute the roles played by the nanowire arrays to simultaneously