Enhanced ZnO based solar cell efficiency by piezo-phototronic effect

We report piezo-phototronic effects on the electrical properties of a Schottky contact metal/ZnO(n) solar cell. The piezo-phototronic effect is a three way coupling effect of piezoelectric, semiconductor and photonic properties occurring in non-central symmetric semiconductor materials when an applied strain to a semiconductor generates a piezoelectric potential controlling the carrier generation, transport, separation and/or recombination at the junction. The purpose of the present study is to determinate the influence of piezoelectric polarization on the electrical characteristics of this solar cell. Results show that the stress causes an increase of the electric field in the region where the piezoelectric fields are located. The sign of the stress proves that if it is positive (extensive strain), the effective barrier height increases which reduces the flow of electrons and thereafter is considered as a limiting factor for photovoltaic conversion, However, if the stress is negative (compression strain), a significant improvement of photovoltaic efficiency is obtained. Using the piezoelectric effects created by an external stress, our study provides not only a theoretical understanding about the piezo-phototronic effects on the characteristics of a solar cell but also assists for the possible design improvement allowing to increase.