Enhanced ferroelectric photovoltaic effect in semiconducting single-wall carbon nanotube/BiFeO₃ heterostructures enabled by wide-range light absorption and efficient charge separation

The interfacial electronic band structures of photovoltaic heterostructure devices greatly affect their light absorption and charge-transport properties and thus their photovoltaic performance. In this work, we report an enhanced ferroelectric photovoltaic effect in a semiconducting single-walled carbon nanotube (S-SWCNTs)/ferroelectric BiFeO₃ (BFO) heterostructure. A wide range of light absorption was possible in this structure owing to the low bandgaps of the S-SWCNTs (0.2-2.1 eV) and BFO (2.2-2.7 eV). The heterostructure also enabled efficient charge separation owing to the strong built-in electric field resulting from the synergic effect of the formation of p-f-n junctions (p-type S-SWCNTs/ferroelectric (f) BFO/n-type Nb:SrTiO₃) and the introduction of a polarization-mediated internal field in the ferroelectric BFO layer. Compared with a single-layer device (Pt/BFO/Nb:SrTiO₃), the heterostructure device (Pt/S-SWCNTs/BFO/Nb:SrTiO₃) exhibited substantial enhancement of the photovoltaic performance. The open-circuit photovoltage and short-circuit photocurrent density reached up to 0.23 V and -7.52 mA cm^-2 (corresponding to a photo-conversion efficiency of 4.40%) under one-sun illumination, respectively, after optimization of the ferroelectric layer thickness and appropriate interfacial band alignment. Moreover, by applying switchable electric polarization, this heterostructure could be tuned, enabling the development of controllable photovoltaic devices. Our findings demonstrate that the synergistic integration of materials with different functionalities is a promising approach for the design of photovoltaic devices with tunable performance.