Process optimization of Al-doped zinc oxide films as a window layer for Cu(In,Ga)Se2 thin film solar cells

• Published in: Applied surface science 2013-11, Vol.284, p.379-385
• Main Authors: Li, Zhao-Hui, Kwon, Sang Jik
• Format: Article
• Language: English
• Subjects: Al-doped ZnO (AZO); Aluminum; Azo; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; COPPER INDIUM SELENIDE; COPPER SELENIDE; Cross-disciplinary physics: materials science; rheology; Cu(In,Ga)Se2 (CIGS) thin film solar cells; DEPOSITION; DOPING; Exact sciences and technology; In-line pulsed-DC sputtering; Optimization; OXIDE FILMS; OXIDES; Oxygen concentration; Photovoltaic cells; Physics; Solar cells; THIN FILMS; ZINC OXIDE
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2013.07.108

•Al-doped zinc oxide (AZO) film is deposited using the in-line pulsed-DC sputter.•Oxygen concentration is varied to optimize AZO films for Cu(In,Ga)Se2 solar cells.•The electrical, optical, and structure properties of AZO films are analyzed.•The optimized AZO film is obtained when it is deposited under pure Ar ambient. Al-doped zinc oxide (AZO) thin film was deposited by an in-line pulsed-DC magnetron sputtering system for Cu(In, Ga)Se2 (CIGS) solar cell and optimum process conditions were analyzed. Of several process parameters, oxygen ratio to argon gas in the sputtering ambient was intensively investigated. As increasing the oxygen concentration from 0% to 2%, carrier concentration decreased from 4.8×1020 to 9.7×1017cm−3 and Hall mobility reduced from 6.1 to 1.1cm2/Vs. Resultantly, the resistivity of the AZO film increased significantly from 2.2×10−3 up to 5.9×10−1Ωcm as increasing the oxygen concentration. This was due to the effect of the scattering mechanism depending on the role of the oxygen in the AZO film. The average transmittance in the range of visible light was lowest as about 74% in the film deposited without oxygen. By the way, the optical band gap was obtained with the most large value of 3.6eV in the film deposited without oxygen. For examining the feasibility as a window layer, the optimal AZO film deposited without oxygen was applied for making the CIGS solar cell. In this CIGS solar cell, the absorber layer was formed by using the rapid thermal annealing method of CuGa/In metal precursors. The cell was satisfactorily operated with the efficiency of 7.69% even though the cell was not optimized for the buffer layer and the composition of the absorber, and had no metal grids and anti-reflection layer.