First principles study of the electronic structure and photovoltaic properties of β-CuGaO₂ with MBJ + U approach

Abstract

Based on the density functional theory, the energy band and electronic structure of β-CuGaO2 are calculated by the modified Becke-Johnson plus an on-site Coulomb U (MBJ + U) approach in this paper. The calculated results show that the band gap value of β-CuGaO2 obtained by the MBJ + U approach is close to the experimental value. The calculated results of electronic structure indicate that the main properties of the material are determined by the bond between Cu-3d and O-2p energy levels near the valence band of β-CuGaO2, while a weak anti-bond combination is formed mainly by the O-2p energy level and Ga-4s energy level near the bottom of the conduction band of β-CuGaO2. The β-CuGaO2 thin film is predicted to hold excellent photovoltaic performance by analysis of the spectroscopic limited maximum efficiency (SLME) method. At the same time, the calculated maximum photoelectric conversion efficiency of the ideal CuGaO2 solar cell is 32.4%. Relevant conclusions can expand β-CuGaO2 photovoltaic applications.

Pulsed laser deposition of β-NaGaO2: significant dependence of sodium fraction, morphology, and phases of the film on deposition position in the plume

“…β-NaGaO 2 has recently attracted attention because it is a precursor material of β-CuGaO 2 , which is a narrow band gap oxide semiconductor (E g = ∼1.5 eV) with a wurtzite structure and expected to be an absorber material in all-oxide and toxic-element-free thin film solar cells. [1][2][3][4][5][6] For enhancing the electrical and optical properties of β-CuGaO 2 , electronic defects arising from structural point defects in β-CuGaO 2 should be reduced. For this purpose, stoichiometric and highquality β-NaGaO 2 precursor films are required, because β-CuGaO 2 is synthesized via ion-exchange of β-NaGaO 2 and the composition of the resulting β-CuGaO 2 is thus determined by that of the β-NaGaO 2 precursor.…”

Fermi Energy Limitation at β-CuGaO2 Interfaces Induced by Electrochemical Oxidation/Reduction of Cu

“…Recently, Suzuki et al proposed that multinary wurtzite-type oxide semiconductors containing Cu + have a direct band gap in the visible wavelength region (< 3 eV) and can be applied for photoelectric conversion devices . β-CuGaO 2 possesses attractive physical properties; it has a direct band gap of 1.5 eV and a large absorption coefficient higher than 10 5 cm –1 , realizing a theoretical maximum conversion efficiency of 32% . In addition, it consists of relatively safe and abundant elements and is practically stable at ambient conditions .…”

“…7 β-CuGaO 2 possesses attractive physical properties; it has a direct band gap of 1.5 eV 8 and a large absorption coefficient higher than 10 5 cm −1 , 9 realizing a theoretical maximum conversion efficiency of 32%. 10 In addition, it consists of relatively safe and abundant elements and is practically stable at ambient conditions. 11 Its intrinsic p-type conduction without an intentional doping 8 arises from the presence of Cu vacancies 12 similar to the intrinsic p-type nature of Cu 2 O, 13,14 which enables the formation of p/n junctions with various n-type oxide semiconductors such as ITO or ZnO.…”