Theoretical exploration of p-doped BiFeO3: models, screening, and applications
Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
Final Report Abstract
A fundamental understanding of aliovalent and isovalent doping effects in BiFeO3 was reached. This was carried out as extensive study, that explicitly treated most elements and allowed estimates for remaining elements, based on the trends found on the large test set. With this study, surprising doping effects can clearly be attributed to other effects, such as the formation of oxygen vacancies. A setup for a thorough theoretical description of this material was established. With these studies, everything is in place to employ promising dopants to form actual p-doped materials and then pn-junctions. The complex interplay with and prevention of defects, however, will require further studies. In addition to this knowledge on possible future oxide electronics, I gained insight into layered hybrid perovskites (HP). In particular on how the decoupling of two-dimensional (2D) sheets, which are only loosely coupled along the stacking direction, affects the electronic structure compared to conventional 3D HPs. The phononic and excitonic properties of our model compound were analyzed in detail in collaboration with experiments. These studies help the design and understanding of future combined 2D/3D HPs or layered HPs as coating layers for 3D HPs, which are promising routes to create photovoltaic (PV) tandem cells and to tackle the instability of traditional 3D HPs towards moisture. Going a step further in tuning the structure of HPs to find possible materials for next generation HP PVs, I developed inverse-hybrid perovskites (IHPs) as new materials class and perovskite modification. This combination of inverse (or anti) and hybrid perovskites moves the hydrophilic organic cation to the B-site, which is usually stronger bound in the perovskite crystal structure. The materials we found display a variety of interesting electronic properties. Most notably, we find with MA3 FNi and MA3 FPb two materials that are promising prospects for lead-free perovskite PVs. Stability analysis suggests that these and other compositions should be accessible experimentally. Funding this project also allowed to finalize work on bottom-up synthesis of extended organic networks by surface assisted Ullmann coupling. These works were important steps towards templating precursors and their temperature-controlled linkage to 2D networks, as well as the understanding of the bis-acetylid bond network, which is the intermediate step in such reactions.
Publications
- “Adding to the perovskite Universe: Inverse-Hybrid Perovskites”, ACS Energy Lett., 2017, 2, 2681–2685
Gebhardt, J., Rappe, A. M.
(See online at https://doi.org/10.1021/acsenergylett.7b00966) - “Influence of the Dimensionality and Organic Cation on Crystal and Electronic Structure of Organometalic Halide Perovskites”, J. Phys. Chem. C , 2017, 121, 6569–6574
Gebhardt, J., Kim, Y., Rappe, A. M.
(See online at https://doi.org/10.1021/acs.jpcc.7b00890) - “Doping of BiFeO3 : A comprehensive study on substitutional doping”, Phys. Rev. B , 2018, 98, 125202
Gebhardt, J., Rappe, A. M.
(See online at https://doi.org/10.1103/PhysRevB.98.12520) - “Transition Metal Inverse-Hybrid Perovskites”, J. Mater. Chem. A, 2018, 6, 14560
Gebhardt, J., Rappe, A. M.
(See online at https://doi.org/10.1039/c8ta02785d)
