First-principles study of Ti host doping effect to stabilize Si guest doping in Fe2O3 hematite.

Si is well-known n-type dopant which enhances the photo-electrochemical (PEC) response of hematite electrodes, due to the improvement in conductivity by increased charge carrier concentrations. Owing to its limited doping ratio, many researchers focus on finding co-doping candidates to further increase Si doping ratio, and p-type dopants are generally proposed for the benefit of satisfying charge neutrality. However, using first-principle DFT calculations, we found that n-type host dopant Ti in hematite lowers the formation energy of n-type guest Si doping by around 1 eV, possibly increasing the Si doping ratio drastically. Although Ti is n-type dopant generating excess charge, it forms local holes in nearby Fe atoms, which stably host the additional n-type guest dopant, Si. For PEC enhancement, we suggest that n-type and n-type co-doping could be a better way both to stabilize the doping structure and increase the carrier concentrations than the conventional p-type and n-type co-doping.