title: Tuning the Band Gap of Cu₂ZnSn(S,Se)₄ Thin Films via Lithium Alloying.
abstract: Alkali metal doping plays a crucial role in fabricating high-performance Cu(In,Ga)(S,Se)2 and Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells. In this study, we report the first experimental observation and characterizations of the alloyed Li(x)Cu(2-x)ZnSn(S,Se)4 thin films. It is found that Cu(+) ions in Cu2ZnSn(S,Se)4 thin films can be substituted with Li(+) ions, forming homogeneous Li(x)Cu(2-x)ZnSn(S,Se)4 (0 ≤ x ≤ 0.29) alloyed thin films. Consequently, the band gap, conduction band minimum, and valence band maximum of Li(x)Cu(2-x)ZnSn(S,Se)4 thin films are profoundly affected by Li/Cu ratios. The band alignment at the Li(x)Cu(2-x)ZnSn(S,Se)4/CdS interface can be tuned by changing the Li/Cu ratio. We found that the photovoltaic parameters of the Li(x)Cu(2-x)ZnSn(S,Se)4 solar cell devices are strongly influenced by the Li/Cu ratios. Besides, the lattice constant, carrier concentration, and crystal growth of Li(x)Cu(2-x)ZnSn(S,Se)4 thin films were studied in detail.
authors.affiliation: State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , 5625 Renmin Street, Changchun, Jilin 130022, China.
authors.forename: Yanchun
authors.initials: Y
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , 5625 Renmin Street, Changchun, Jilin 130022, China.
authors.forename: Xiaojiao
authors.initials: X
authors.lastname: Kang
authors.affiliation: State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , 5625 Renmin Street, Changchun, Jilin 130022, China.
authors.forename: Lijian
authors.initials: L
authors.lastname: Huang
authors.affiliation: State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , 5625 Renmin Street, Changchun, Jilin 130022, China.
authors.forename: Daocheng
authors.initials: D
authors.lastname: Pan
keywords: CZTSSe thin films; Li alloying; band gap tuning; kesterite; solar cells