Anomalous photovoltaic effect with high fill factor in Fe³⁺-Li⁺ co-doped ZnO films

Integrating high fill factor (FF) with above-bandgap photovoltage has been of fundamental importance in building high-power conversion efficiency (PCE) devices based on anomalous photovoltaic effect. Herein, the discovery of high performance anomalous photovoltaic effect under white light in designed Zn_1–2x(Fe_xLi_x)O films fabricated by a low-cost sol-gel process is reported, where above-bandgap photovoltage, improved FF, a switchable photoresponse of 34.1 mA/W, and a PCE of 10.3 % are obtained. It is found that the photovoltaic effects are closely related to the ferroelectricity of the co-doped films. A mechanism based on serial connection of poled ferroelectric regions and junctions is proposed to interpret the photovoltaic effects with high FF in Fe³⁺-Li⁺ co-doped ZnO films, where the junction is formed between the ferroelectric and weak-ferroelectric regions. This photo-to-electron conversion model suggests a route to design and fabricate cost-efficient solar cell and other optoelectronic devices.