Enhanced Photovoltaic Effect in Single-Wall Carbon Nanotube/BiFeO3 Heterostructure

Abstract

Photovoltaic effect in ferroelectric materials have been revisited with energy applications because of visible-light-absorbing ferroelectrics and an anomalous photovoltaic effect, such as extremely large, above-band-gap voltages and polarization-induced electron-hole separation. BiFeO3, having a relatively low band-gap (~2.7 eV) is a potential visible-light-absorbing photoferroelectric materials. However, it is still limited to further enhancing photovoltaic efficiency due to a low photocurrent. In this work, we report an enhanced photovoltaic effect in single-wall carbon nanotubes (SWCNTs)/BiFeO3 photovoltaic heterostructures. High-purity metallic (M)- and semiconducting (S)-SWCNTs were seperated by using gel chromatography method and BiFeO3 thin films were grown on Nb:SrTiO3 substrate by pulsed laser deposition. M- and S-SWCNTs thick films are incorporated onto BiFeO3 for photovoltaic devices. For single BiFeO3/Nb:SrTiO3, we observed clear switchable diode and photovoltaic effects depending on ferroelectric polarizatioin directions. The S-SWCNTs/BiFeO3/Nb:SrTiO3 heterostructrues exhibited a large enhancement of photovoltaic performance compared with those of BiFeO3/Nb:SrTiO3 or M-SWCNTs/BiFeO3/Nb:SrTiO3. This heterostructure allowed a strong built-in field to be generated at the interface or the ferroelectric layer to efficiently separate photogenerated charge carriers and a wide range-light absorption due to near infrared-light absorbing S-SWCNTs and visible-light-absorbing BiFeO3. Under light illumination, this junction showed short-circuit current density of 1.73 mA/cm2 and open-circuit voltage of 0.21 V. Furthermore photovoltaic response was influenced by BiFeO3 thickness and SWCNT’s character. Our result implied that the heterostructure of high purity S-SWCNTs and high quality ferroelectric thin films could provide a route to highly efficient Photovoltaic devices.