Figure 4
(a) The sequence of applying external poling voltage: +8 V → 0 → −8 V → 0 → +8 V, which is marked by the arrow polylines 1 and 2. The up and down arrows in green rectangles represent the schematic ferroelectric domain directions in the PZT layer. Note that the direction of spontaneous polarization in ZnO layer is not changed by external applied voltages. (b–d) The photovoltaic Voc and Jsc hysteresis loops of three samples as a function as poling voltage (VP): (b) ITO/PZT/Au, (c) ITO/PZT/ZnO/Au and (d) ITO/ZnO/PZT/Au.
