Elsevier

Ceramics International

Volume 42, Issue 12, September 2016, Pages 14036-14040
Ceramics International

The ferroelectric photovoltaic effect of BiCrO3/BiFeO3 bilayer composite films

https://doi.org/10.1016/j.ceramint.2016.06.010Get rights and content

Abstract

This work involves an investigation of the structure, ferroelectricity, optical band-gap, photovoltaic spectral response and J-V performance of BiCrO3/BiFeO3 bilayer composite films prepared via the solution-gelation technique. It is shown that the enhanced ferroelectric properties are observed for BiCrO3/BiFeO3 bilayer composite films by interaction resulting from the coupling between BiFeO3 and BiCrO3 layers. The photovoltaic spectral responses of the normalized current for BiCrO3/BiFeO3 bilayer composite films presents a noteworthy red-shift towards visible region compared with the pure BiFeO3 films and the pure BiCrO3 films. Thus photovoltaic response is attributed to the narrow band-gap of BiCrO3/BiFeO3 bilayer composite films. The short circuit current density and open circuit voltage of the BiCrO3/BiFeO3 bilayer composite films under white-light illumination are much higher than the values of BiFeO3 and BiCrO3 films. The present work provides an available way of controlling photovoltaic response of ferroelectric films and accelerating its application in light sensors, light drivers and ferroelectric photovoltaic cells.

Introduction

Semiconductor photovoltaic materials have exhibited their outstanding advantages such as mature technology and relatively high conversion efficiency. For semiconductor photovoltaic materials, photons with energy higher than the band gap are absorbed to produce electron–hole pairs which are separated by the internal field in the p–n junction and collected with the electrodes. Consequently, the photo-induced voltage is limited by the energy barrier height at the interface region and usually smaller than the semiconductor band-gap [1]. Therefore, the ferroelectric photovoltaic effect has been attracted a great deal of attention due to its efficient polarization-governed mechanism of charge separation and ability to generate above band-gap voltages [2]. Different from the traditional junction-based semiconductor photovoltaic effect, ferroelectric photovoltaic effect is generally thought that the internal electric field originates from ferroelectric polarization. Ferroelectric photovoltaic effect does not require an asymmetric interface and its photovoltage is not limited by the band gap of the materials. Therefore, it can generate above band-gap voltage. So steady-state photo-current can exist in a homogeneous medium under uniform illumination, which is called bulk photovoltaic effect [3]. However, the wide band-gap ferroelectric materials such as LiNbO3, BaTiO3, Bi4Ti3O12 can not effectively absorb visible light so that the intrinsic photovoltaic characteristics are unsatisfactory. Compared with conventional ferroelectric materials, the band-gap of BiFeO3 materials is narrow, which eliminate photovoltaic response area in the near ultraviolet region [4]. Special attention is paid to bismuth ferrite BiFeO3 (BFO), multiferroic perovskite with rhombohedral structure is known to simultaneously display both ferroelectric and ferromagnetic behavior at room temperature [5]. Due to its unique properties, BiFeO3 is a suitable material for plethora of possible applications, such as photocatalytic water splitting, smart sensing, spintronics and magnetic data storage. Periodically arranged narrow domains enable facile transport of generated charge across the BiFeO3, resulting a output voltage exceeding that of a band-gap [6]. Each of the domains is separated by walls and can be observed as an independent device, when linked in series create efficient pathway for movement of electrons, earning the nickname “bucket brigade” [7]. BiFeO3 is recognized as a potential candidate for photovoltaic applications due to its relatively narrow band-gap in comparison to other ferroelectric materials. Therefore, it is possible to obtain strong photovoltaic effect in near ultraviolet for BiFeO3 films and it is necessary to further decrease the band-gap in order to regulate the photovoltaic response region from the near ultraviolet region towards visible region.

Therefore, this work aims to prepare BiCrO3(BCO)/BiFeO3(BFO) bilayer composite films to regulate the band-gap to obtain strong photovoltaic spectral response in visible region. The structure, ferroelectricity, optical band-gap, photovoltaic spectral response and J-V performance were investigated systematically. The photovoltaic spectral responses of the normolized current for BCO/BFO bilayer composite films show a noteworthy red-shift towards the visible region comparing with the pure BiFeO3 films and the pure BiCrO3 films. The short circuit current density and open circuit voltage of the BiCrO3/BiFeO3 bilayer composite films under white-light illumination are much higher than the values for BiFeO3 and BiCrO3. These results reveal photovoltaic effects presented in these device structures. This work provides a feasible method on making the effective ferroelectric photovoltaic response in the visible wavelength for BiFeO3 based films. The origins of the thus photovoltaic behaviors were detailedly discussed.

Section snippets

Experiment

The BiCrO3/BiFeO3 bilayer composite films were grown on Pt/Ti/SiO2/Si(100) substrates by using solution–gelation technique. To make a good-quality precursor solution, Bi(NO3)3·5H2O and Fe(NO3)3·9H2O were dissolved in proper proportions of 1.1:1 into ethylene glycol methyl ether at the same time and magnetically stirred for two hours. Bi(NO3)3·5H2O was dissolved with a 10% Bi excess for compensating the loss during annealing. Then Bi(NO3)3·5H2O and Cr(NO3)3·9H2O were added in proper proportions

Results and discussion

Fig. 1 shows the XRD pattern of BiCrO3, BiFeO3 and BCO/BFO films deposited on a Pt/Ti/SiO2/Si(100) substrate. The diffraction peaks of BiFeO3 films were indexed with reference to the polycrystalline distorted rhombohedral perovskite structure matched well with the JCPDS no. 86-1518 for R3c space group since (104) and (110) planes are almost completely separated [8]. The diffraction peaks of BiCrO3 films match very well with the JCPDS no. 04-0570 for tetragonal structure. Moreover BCO/BFO

Conclusions

BCO/BFO bilayer composite films were successfully prepared using a sol–gel process and characterized by X-ray diffraction, ferroelectricity, photovoltaic spectral response, ultraviolet–visible absorption spectra and J-V measurements. The analysis of XRD pattern confirms pure-phase multiferroic materials with BCO/BFO bilayer composite films containing BiCrO3 and BiFeO3. It is observed that improved ferroelectric property and leakage current density in the BCO/BFO bilayer composite films due to a

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (Grant nos. 11264026, 11564028 and 51202103), and Inner Mongolia Science Foundation for Distinguished Young Scholars (Grant no. 2014JQ01), the Youth Science and Technology Talents Foundation of Inner Mongolia (Grant no. NJYT-B02).

References (14)

There are more references available in the full text version of this article.

Cited by (0)

View full text