Fig. 1. Schematic diagram of shallow (a) and deep (b) level defect states of neutral oxygen vacancy. The dotted lines in the figure represent the special k points used in supercell computation^[10]

Fig. 2. Formation energy of V_Cd, calculated with HSE06, at different valence states with the variation of Fermi energy levels and the structural symmetry^[31].

Fig. 3. Formation energy and charge transition levels of CdTe eigendefects calculated with HSE06^[32]

Fig. 4. Variations of the Fermi level, carrier density, and defect concentration of CdTe with temperature and chemical potential^[37].

Fig. 5. The formation energies of P_Te and As_Te under rich Cd (a) and rich Te (b) conditions with the Fermi energy levels; (c) the lattice torsion when AX center is formed^[31].

Fig. 6. The formation of related defects formed by Na incorporation into CdTe vs. the Fermi energy level under the conditions of rich Cd and rich Te^[31].

Fig. 7. Two common grain boundaries in CdTe: (a) ; (b) centered on Te^[64]

Fig. 8. The intrinsic defect formation energy of CuInSe₂ with the Fermi energy level^[77].

Fig. 9. The transition level of the intrinsic defect of CuInSe₂^[77].

Fig. 10. The formation energy of intrinsic defects in CuInSe₂ and CuGaSe₂vs. the Fermi energy level.

Fig. 11. The photoelectric conversion efficiency and open circuit voltage of CuIn_1–xGa_xSe₂vs. the bandgap value^[80].

Fig. 12. of CuInSe₂ grain boundary: (a) Supercell structure; (b) local atomic structures at grain boundaries; (c) state density, energy band structure and differential charge density at the grain boundary; (d) the process of forming a defect band by a wrong bond at the grain boundary^[91].

Fig. 13. The chemical potential range of CZTS in the plane and ^[111].

Fig. 14. The formation energy of CZTS intrinsic defect at chemical potential points A, B, C, D, E, F and G^[111].

Fig. 15. The formation energy of CZTS and CZTSe intrinsic defects vs. the Fermi energy level at A^[110].

Fig. 16. The transition energy levels of CZTS and CZTSe intrinsic defects^[110].

Fig. 17. The effect of composite defects in CZTS and CZTSe on the band edge^[110]

Fig. 18. Wrong bond and the corresponding defect state at CZTSe grain boundary^[126].

Fig. 19. The CBM and VBM differential charge density, band structure and state density of CH₃NH₃PbI₃^[11].

Fig. 20. Transition mechanism of various solar cell mate-rials^[127].

Fig. 21. (a) The chemical potential of CH₃NH₃PbI₃ at equilibrium growth; (b)—(d) the defect formation energy at the intrinsic point of CH₃NH₃PbI₃vs. the chemical potential^[11].

Fig. 22. The transition energy level of the eigenpoint defect of CH₃NH₃PbI₃^[11].

Fig. 23. (a) Pb dimer in intrinsic defect V_I^–; (b) I trimer in I_MA⁰ of the intrinsic defect^[144].

Fig. 24. The partial structure diagrams of non-dimer (a) and the dimer structure diagrams of V_I (b); (c) formation mecha-nism of DX central defect energy level in CH₃NH₃PbI₃.