Effect of the Magnetostriction Induced on the Crystalline Structure of Nanoparticulate TiO2 Photoanodes and Their Relationship with the Photovoltaic Response of Black-Dye Sensitized Solar Cells

Abstract

The study of ferromagnetism (FM) in semiconductor oxides having non-cubic crystalline structures (e.g. TiO2) is attractive due to their applications in spintronics [1]. FM can be activated in TiO2 nanomaterials by promoting oxygen vacancies (VO) located in paramagnetic defected sites Ti3+VOTi4+. In this context, the VO can induce in Ti3+-doped TiO2 structures remarkable magnetic anisotropy energy (MAE) of 6.51x106 erg/cm3, thus indicating the magnetic saturation (Ms) should be achieved by applying external magnetic fields (MFs) of ~425 gauss [2,3]. Therefore, magnetostriction can be observed in ferromagnetic TiO2 films containing Ti3+VOTi4+ sites as a phenomenon in which their dimensions and shapes are changed when they are magnetized. In this work, black dye-sensitized solar cells (BD-SSC) were prepared using TiO2 nanoparticle films enriched by Ti3+VOTi4+ sites, to gain an understanding of the effects of magnetostriction on the photovoltaic responses of BD-SSC. In this way, photocurrent density-cell potential plots were obtained for the BD-SSC in the absence and presence of MFs having intensities of 125, 250, 500, 1000, and 2000 gauss. MFs lines were parallel applied to the surface of the BD-sensitized TiO2 photoanodes. Our results indicated that the photogenerated electron transport through the dyed TiO2 photoanodes was not limited by electron transfer to I3 - anions at the electrolyte in the absence or the presence of MFs, because all the values for the open-circuit potential (-Eoc ~ 0.553±0.014 V) remain constant. On the contrary, the obtained values for the short-circuit current density Jsc and the global conversion efficiency, revealed that both parameters increased as a function of the MFs intensities, thus indicating that the magnetic lines were responsible for decreasing the degree of disorder (0<b<1) of the electron-traps at the intra-bandgap state's distribution of the TiO2 film (Jsc is proportional to Q1/ b where Q is the number of trapped electrons) [4,5].[1] M. Stiller et al., Front. Phys., 11(2023)1124924.; [2] D. Kim et al., J. Phys.: Condens. Matter, 21(2009)195405.; [3] B. Shao et al., J. Appl. Phys., 115(2014)17A915. [4] N. Kopidakis et al., J. Phys. Chem. B, 107(2003)11307. [5] J. van de Lagemaat et al., J. Phys. Chem. B, 104(2000)4292. Acknowledgements The authors thank the National Council for Science and Technology (CONACyT) Mexico for the funding support (grants CB No. 258789 and FOINS No. 3838). JIVN thanks CONACyT for his doctoral fellowship support (grant No. 893260).