First-principles study of La and Mg doped/co-doped TiO2 for tailoring trap states in the electron transport layer of perovskite solar cells

Doping TiO 2 with La and Mg shows promise in enhancing its performance as an electron transport layer (ETL) in perovskite solar cells. Yet, a comprehensive understanding of the specific contributions of these dopants to TiO 2 properties remains elusive. In the present study, we employ density functional theory calculations with the Hubbard U correction (DFT+U) to explore the structural and electronic characteristics of La-doped TiO 2 and two structural variants co-doped with La and Mg. In one of the two co-doped materials, La and Mg atoms replace O and Ti, respectively (TiO 2 -La (1) -Mg (1) ), while in the other, La and Mg substitute for two Ti atoms (TiO 2 -La (2) -Mg (1) ). The singularly La-doped material, TiO 2 -La (3) , is formed by replacing one Ti atom with an La atom. Our comprehensive analysis, formation energy and Koopman's calculations, aimed to determine structural stability. The results indicate that under O-rich or Ti-rich conditions, TiO 2 -La (2) -Mg (1) shows the most promising characteristics. Assessment of the electronic structure reveals that TiO 2 -La (2) -Mg (1) and TiO 2 -La (3) have a lower density of trap states compared to TiO 2 -La (1) -Mg (1) . Analysis of the optical spectrum indicates that TiO 2 -La (2) -Mg (1) exhibits the highest absorption ability in visible range, closely followed by TiO 2 -La (1) -Mg (1) and TiO 2 -La (3) , respectively. In conclusion TiO 2 -La (2) -Mg (1) and TiO 2 -La (3) are identified as the most promising structures, emphasizing the importance of striking a balance between trap states and a narrowed band gap to achieve optimal performance. Furthermore, our findings suggest the potential for efficient TiO 2 co-doped structures under specific growth conditions, highlighting a novel avenue for exploration in both theoretical and experimental domains. • TiO 2 -La (2) -Mg (1) emerges as the most promising ETL material. • La substitution to TiO 2 introduces significant trap states. • For better ETL, trap state has to be fine tune with band gap. • La-Mg dope TiO 2 performance could enhance by applying O-rich or Ti-rich growth condition during synthesizing.