Evaluating the C, N, and F Pairwise Codoping Effect on the Enhanced Photoactivity of ZnWO4: The Charge Compensation Mechanism in Donor–Acceptor Pairs

Abstract

We perform first-principles density function theory calculations to study the geometric and electronic structures and photoactivity of C, N, and F monodoped and pairwise codoped ZnWO4. By incorporating single C, N, or F into ZnWO4, considering substitutional as well as interstitial locations of dopants in the ZnWO4 lattice, we find that the photon transition energy decreases to varying degrees, while the partially occupied states induced by the impurity are located in the gap, which may act as recombination centers and reduce the photoinduced current density. By analyzing the defect wave function character, we propose several pairwise codoped ZnWO4 systems, such as Cs+2Fs-, Ns+Fs-, Ci+2Ns-, and Ni+Fs-codoped ZnWO4, to passivate the partially occupied states in the monodoping systems by the charge compensation effect in the donor–acceptor pairs, resulting in occupied states in the gap and reducing the formation energy compared with the monodoping systems. The Cs+2Fs and Ns+Fs codoping do not narrow the host band gap of ZnWO4, while they decrease the excitation energy from the occupied gap states to the conduction band minimum to some extent. The Ci+2Ns and Ni+Fs codoping in the ZnWO4 can red shift the transition energy of photoexcited electrons from the impurity levels to the conduction band minimum to the ideal visible-light region; therefore, the Ci+2Ns codoping can decrease the host band gap of ZnWO4 by about 0.3 eV. Our results show that the partially occupied states in the monodoping ZnWO4 can be passivated by the charge compensation effect in the donor–acceptor pairs, thus improving the photoactivity and reaching the visible-light photoactivity for ZnWO4.