Carrier transport engineering in a polarization-interface-free ferroelectric PN junction for photovoltaic effect

The carrier transport performances play key roles in the photoelectric conversion efficiency for photovoltaic effect. Hence, the low carrier mobility and high photogenerated carrier recombination in ferroelectric materials depress the separation of carriers. This work designs a ferroelectric polarization-interface-free PN junction composed with P-type semiconductor BiFeO₃ (BFO) derived from the variable valence of Fe and N-type semiconductor BiFe_0.98Ti_0.02O₃ (BFTO) through Ti donor doping. The integration of the ferroelectricity decides the PN junction without polarization coupling like the traditional heterojunctions but only existing carrier distribution differential at the interface. The carrier recombination in PN junction is significantly reduced due to the driving force of the built-in electric field and the existence of depletion layer, thereby enhancing the switching current 3 times higher than that of the single ferroelectric films. Meanwhile, the carrier separation at the interface is significantly engineered by the polarization, with open circuit voltage and short circuit current of photovoltaic effect increased obviously. This work provides an alternative strategy to regulate bulk ferroelectric photovoltaic effects by carrier transport engineering in the polarization-interface-free ferroelectric PN junction.