A Study of Doping Profile for the Site Selectively Zn‐Doped p‐type Cu(In,Ga)Se₂ Thin Film for Solar Cell

Abstract

An attempt is made to dope Zn impurity selectively at the In site in Cu(In,Ga)Se2 (CIGS) by supplying Zn at the first stage of a three‐stage method. Increase in carrier concentration in p‐type CIGS leads to increase in an open circuit voltage and a conversion efficiency (η). The Zn impurity loaded in (In,Ga)2Se3 a the 1st stage is expected to make a substitutional ZnIn acceptor in CIGS, which leads to increase in carrier concentration. The Zn doping profile at the 1st stage is expected to be reflected in the acceptor (ZnIn) depth profile. Acceptor in‐depth profile is expected to be changed by the Zn flux. The room‐temperature PL spectra of the CIGS:Zn exhibited peak shift to higher energy by 10–50 meV depending on the Zn‐doping condition due to the change of band gap energy. The carrier in‐depth profile is characterized using a capacitance‐voltage method for ZnO/CdS/CIGS:Zn solar cells. Carrier concentration of Zn‐loaded samples increase by one order of magnitude as compared with that in the intentionally undoped CIGS samples. The relationship between the Zn‐doping profile and solar cell characteristics is examined. Results are also discussed in terms of the back surface field created by the Zn‐doping profile.