School of Engineering and Materials Science Research

Efficiency calculations for nanostructured energy harvesters.

We use controlled bending of a ZnO/PEDOT:PSS diode at known rates to measure the efficiency of the device in converting the applied mechanical into output electrical energy. By subtracting the energy required to bend a blank substrates from that required to bend a complete device we measure the mechanical energy input into the nanostructured diode as 330±2 nJcm-2. The electrical energy output is calculated by integrating the product of the short circuit current and open circuit voltage over time. This gives a measured external efficiency of the device at a bending rate of 500 mm/min of 0.0067 %. The efficiency increases exponentially with bending rate, though this increase must slow as the mechanical coupling efficiency is approached to give an efficiency that is limited by the mechanical coupling efficiency of 24% for ZnO.

Schematic of the device tested

Energy calculations