[16a-F201-1~12] 13.10 Compound solar cells

▲ [16a-F201-4] Application of Zn_1-xMg_xO:Al to transparent conductive oxide of Cu(In,Ga)(S,Se)₂ solar cell

〇(PC)Jakapan Chantana¹, Takuya Kato², Hiroki Sugimoto², Takashi Minemoto¹ (1.Ritsumeikan Univ., 2.Solar Frontierv K.K.)

Keywords:Cu(In, Ga)(S, Se)2 solar cell

19.47%-efficient Cu(In,Ga)(Se,S)₂ (CIGSSe)-based solar cell is obtained by replacing traditional CdS/ZnO buffer layers with Cd_0.75Zn_0.25S/Zn_0.79Mg_0.21O layers to increase short-circuit current density since its external quantum efficiency is increased in a short wavelength range of 320-520 nm. In addition, it was theoretically reported that difference of conduction band minimum (E_C) between transparent conductive oxide (TCO) layer and absorber plays a role in reducing carrier recombination at interface for enhancing the conversion efficiency (η), especially open-circuit voltage (V_OC) and fill factor (FF) [1]. In this work, Zn_1-xMg_xO:Al was utilized as alternative TCO layer in CIGSSe solar cell to experimentally investigate influence of the E_C difference between TCO layer and CIGSSe absorber to boost cell performances, especially V_OC and FF. The difference of E_C between Zn_1-xMg_xO:Al layer and CIGSSe absorber is optimized by varying [Mg]/([Mg]+[Zn]), x. It is demonstrated that Zn_1-xMg_xO:Al films with [Mg]/([Mg]+[Zn]) of 0.1-0.12, enhancing band-gap energy (E_g) to 3.72-3.76 eV, are appropriate as TCO because of their enhanced mobility and decreased carrier density. The addition of 12% Mg into ZnO:Al for TCO layer effectively decreases surface carrier recombination and improves V_OC and FF. This is first experimental proof of the concept for optimizing E_C difference between TCO and absorber to minimize surface carrier recombination. Ultimately, conversion efficiency of CIGSSe solar cell with alternative Cd_0.75Zn_0.25S/Zn_0.79Mg_0.21O/Zn_0.88Mg_0.12O:Al layers is improved over 20%.
[1] M. Murata, J. Chantana, N. Ashida, D. Hironiwa, T. Minemoto, Jpn. J. Appl. Phys. 2015, 54, 032301.