Search

In this study, we report a novel single-wall carbon nanotube (SWCNT)-TiO2 composite photoanode with enhanced thermal conductivity for photovoltaic applications. Thermal chemical vapor deposition technique was used for the growth of high quality SWCNTs. Structural and morphological properties of as synthesized SWCNT and SWCNT-TiO2 composites were inspected using ultra-high resolution transmission electron microscope (UHRTEM) and Raman spectrosctopy. Thermal conductivity of pure titania (TiO2) and SWCNT-TiO2 composites were estimated by an optothermal method. Photovoltaic performance of Dye-sensitized solar cell (DSSC) containing composite photoanodes was studied at various temperatures (ranging from room temperature-323K). We observed a notable decline in the overall photovoltaic performance of the DSSC containing pure TiO2 photoanode at elevated temperatures. Whereas, DSSC with composite photoanodes showed a significant improvement in overall photovoltaic performance consistently at room temperature as well as at elevated temperatures that is believed to be due to the existence of SWCNT and provides a conducting pathway to electrons in trap states and which are released at higher temperature and thus, quench recombination more effectively.

In recent years, BiFeO3 (BFO) thin films showed promising potential towards photovoltaic applications due to its superior ferroelectric properties and optical bandgap lies in the visible region. Among other wide bandgap ferroelectric photovoltaic (Fe-PV) materials (i.e. BaTiO3, LiNbO3 and Pb(Zr,Ti)O3), BFO exhibits large open circuit voltage (VOC), tunable output, and switchable photovoltaic effect. It has been reported that insertion of semiconductor layer to a conventional metal/ferroelectric/metal structure can result into novel heterostructures based photovoltaic cells. However, integration of novel carbon materials in ferroelectric photovoltaic devices has not been very popular. We have studied photovoltaic effect in In2O3-Sn2O3 (ITO)/reduced graphene oxide (rGO)/BiFeO3/Au (metal/semiconductor/ferroelectric/metal heterostructure). We have synthesized graphene oxide using modified hummers method. We spin coated GO solution on ITO substrate and dried overnight at 50oC to achieve thin films. Resultant GO thin films were annealed in NH3:H2 (3:1) atmosphere at 600oC. Electrical measurements confirmed n-type doping in thermally reduced GO (rGO) films. Whereas, BFO act as p-type semiconductor due to charge defects mainly, Oxygen vacancies. BFO films were grown using pulsed laser deposition technique. ITO/rGO/BFO/Au heterostructures shows a reasonable photovoltaic response. Such heterostructure shows short-cicuit current density of 86 µA/cm2. We believe that two built-in fields generated at Au/BFO and BFO/rGO interface are responsible for separation and transport of photo-excited electron-hole pairs. Our work may provide a new way to integrate carbon materials to ferroelectrics to produce heterojunction based solar cells.

We studied switchable photovoltaic and photo-diode characteristics of Pt/(Bi0.9Sm0.1)(Fe0.97Hf0.03)O3/ LaNiO3 (Pt/BSFHO/LNO) heterostructures integrated on Si (100). The directions of photocurrent (JSC) and rectification are found to be reversibly switchable after applying external poling voltages. In pristine state, metal-ferroelectric-metal capacitor Pt/BSFHO/LNO shows JSC ∼ 32 μA/cm2 and VOC ∼ 0.04 V, which increase to maximum value of JSC ∼ 303 (−206) μA/cm2 and VOC ∼ −0.32 (0.26) V after upward (downward) poling at ±8 V. We believe that Schottky barrier modulation by polarization flipping at Pt/BSFHO interface could be a main driving force behind switchable photovoltaic and rectifying diode characteristics of Pt/BSFHO/LNO heterostructures.

We are reporting on the improved ferroelectric and photovoltaic properties of (Nd3+, V5+) co-doped (Bi0.95Nd0.05)(Fe1−x V x )O3 (BNFVO) (x = 0.01, 0.03) thin films grown by PLD. BNFVO thin films showed reduced leakage current, lower optical bandgap, and improved ferroelectricity compared to BFO films, which can be explained by valance change and extinguishing oxygen vacancies due to the doping effect. Piezoresponse force microscopy measurements showed an improved domain back switching in doped thin films indicating that the suppression of oxygen vacancies offset the effect of polarization flipping caused by doping. Further, we found a relatively stable and enhanced photovoltaic effect in BNFVO films with an order of magnitude higher photocurrent and almost doubled photovoltage in comparison to BFO films, which can be explained by less recombination between hopping electrons and oxygen vacancies. Our results demonstrate the significance of dopant selection to suppress the oxygen vacancies for improved ferroelectric and photovoltaic properties of BFO films.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.