The photovoltaic effect in a [001] orientated ZnO thin film and its physical mechanism

Abstract

We report a new type of photovoltaic effect. The photovoltaic device was constructed using a [001] orientated wurtzite ZnO thin film synthesized by heating Zn(NO₃)₂ solution. The open-circuit voltage (V_oc) and short-circuit current (I_sc) of the ZnO photovoltaic device are 0.16 mV and 0.25 μA, respectively, under 365 nm ultraviolet lamp (3 W) illumination. Current rectification across the top and bottom planes of the ZnO thin film was observed. The photovoltaic and rectifying properties of the ZnO thin film are related to the magnitude of the TC(002). An internal electric field is produced in the ZnO film by spontaneous polarization in the [001] direction. The presence of the internal electric field is the fundamental physical basis of the photovoltaic effect, and a new physical mechanism of photon-to-electron conversion is proposed. The electrostatic potential provides a driving force for flow of the photogenerated electrons and holes in the semiconductor and in an external load, and thus the photo-to-electron conversion is achieved. Our result suggests thin film texturing as a strategy to develop photovoltaic devices beyond p–n junction. In addition, the photo-to-electron conversion model provides new insights into the understanding of the photovoltaic effect in ferroelectric and pyroelectric materials as well as the design and fabrication of advanced solar cells and other electronic and optoelectronic devices.