Extensive Enhancement in Charge Collection Efficiency of Ferroelectric Cr-Doped BFO-Based Solar Cells by Using TiO2 Nanotube Arrays

Abstract

In this article, 100 times or above enhancement in current has been reported in comparison to any of the previously reported BFO-based PV device. This was achieved by fabricating a novel heterostructure junction between ferroelectric Cr-doped BFO (BFCrO) and TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanotubes (T-NTs). The device performance is also compared with BFO/T-NTs junction as well. The Ag/BFO (or BFCrO)/T-NTs/Ti PV cells were developed with BFO (or BFCrO) as the absorber layer, T-NTs were employed as the electron transport layer, with Ti substrate and Ag as bottom and top electrodes, respectively. The remarkable performance of the p-BFCrO/n-T-NTs junction was due to higher absorption in the visible spectrum owing to the stronger ferroelectricity in BFCrO and the large surface area-to-volume ratio of T-NTs. The photovoltaic (PV) performance revealed enhanced current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SC</sub> ) and photovoltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</sub> ) of 7.6 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 0.85 V, respectively. The structural, morphological, and optical properties of both the fabricated structures have been investigated and compared. A well-fitted band structure was realized for the fabricated devices illustrating the band dynamics and carrier flow generation at the interface. The impedance properties confirmed a substantial improvement in the interfacial charge transfer kinetics with an amended driving force for electron-hole pair separation. The enhanced PV performance can be ascribed to the synergetic effect between the polarization induced switching of Cr doping in BFO and the reduced carrier recombination stimulated by highly conductive T-NTs. The structure presented here is promising for developing low cost and efficient PV devices suitable for green energy harvesting applications.