Enhancing the Output Voltage of Piezoelectric Nanogenerators Based on ZnO Nanowires Grown by Chemical Bath Deposition Using Compensatory Cu Doping

Abstract

The screening effect in ZnO nanowires (NWs) coming from the high density of free electrons has emerged as one of the major issues for their efficient integration into piezoelectric devices. Herein, the compensatory Cu doping of ZnO NWs grown by chemical bath deposition in the high‐pH region using Cu(NO3)2 and ammonia as chemical additives is developed and the effects of a postdeposition thermal annealing under oxygen atmosphere are investigated. It is shown that the Cu dopants are incorporated into ZnO NWs with an atomic [Cu]/[Zn] ratio in the range of 50–65 ppm and undergo a migration process into their bulk after thermal annealing. Importantly, the electrical resistivity of Cu‐doped ZnO NWs is found to increase by a factor of 4 compared to unintentionally n‐doped ZnO NWs. The increase is even more pronounced after different thermal annealing, reaching a factor exceeding 100, which is explained by the redistribution of hydrogen‐ and nitrogen‐related defects along with the thermal activation of Cu dopants. Additionally, it is revealed that a rigid piezoelectric nanogenerator based on a Cu‐doped ZnO NW matrix exhibits the highest output voltage and effective piezoelectric coefficient d33eff thanks to the reduction of the screening effect, opening perspectives in the field of piezoelectric devices.