Presently, current solar energy conversion devices are still limited by high cost and low efficiency. The use of non-centrosymmetric materials, ferroelectrics in particular, is a new approach that is being tested for boosting conversion efficiency. Ferroelectric materials show phenomena such as the bulk photovoltaic effect and the anomalous photovoltaic effect as consequence of being non-centro-symmetric.
To improve on this line of work, the electronic and optical properties of Bismuth ferrite (BiFeO3) are theoretically investigated when doped with transition metals (TM) up to 10 %, using the density functional theory within the generalized gradient approximation (GGA) and a simple Hubbard correction (GGA + U). To determine the Band Gap of BiFeO3(BFO):TM calculations were performed using PBEsol pseudopotential with energy cutoffs of 70 Ry. We used the Berry phase formalism of electric polarization to calculate the electric and ionic polarization in BFO:MT. By incorporating dopants in the cationic site, the most favorable results show an increase of the Fermi energy, generating a displacement, that turns out favorable for photovoltaic properties by reducing the the band gap. According to our results, these materials seem to be promising candidates for solar-to-electric energy conversion through the bulk and/or anomalous photovoltaic effects.
Financial support from CoNaCyT, Grants No. 282778 and 280309 and PAPIIT-DGAPA-UNAM Grants No. IN105307 and IN110315 is acknowledged. Two of the authors, E. M-A. and H.-H. thank CoNaCyT for their scholarships.