title: Substitution of Li for Cu in Cu2ZnSnS4: Toward Wide Band Gap Absorbers with Low Cation Disorder for Thin Film Solar Cells.
abstract: The substitution of lithium for copper in Cu2ZnSnS4(CZTS) has been experimentally and theoretically investigated. Formally, the (Cu1-xLix)ZnSnS4system exhibits two well-defined solid solutions. Indeed, single crystal structural analyses demonstrate that the low (x < 0.4) and high (x > 0.6) lithium-content compounds adopt the kesterite structure and the wurtz-kesterite structure, respectively. For x between 0.4 and 0.6, the two aforementioned structure types coexist. Moreover,119Sn NMR analyses carried out on a (Cu0.7Li0.3)2ZnSnS4sample clearly indicate that lithium replaces copper preferentially on two of the three available 2-fold crystallographic sites commonly occupied by Cu and Zn in disordered kesterite. Furthermore, the observed individual lines in the NMR spectrum suggest that the propensity of Cu and Zn atoms to be randomly distributed over the 2c and 2d crystallographic sites is lowered when lithium is partially substituted for copper. Additionally, the first-principles calculations provide insights into the arrangement of Li atoms as a function of the Cu/Zn disorder and its effect on the structural (lattice parameters) and optical properties of CZTS (band gap evolution). Those calculations agree with the experimental observations and account for the evolutions of the unit cell parameters as well as for the increase of band gap when the Li-content increases. The calculation of the formation enthalpy of point defect unambiguously indicates that Li modifies the Cu/Zn disorder in a manner similar to the change of Cu/Zn disorder induced by Ag alloying. Overall, it was found that Li alloying is a versatile way of tuning the optoelectronic properties of CZTS making it a good candidate as wide band gap materials for the top cells of tandem solar cells.
authors.affiliation: Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS , 2 rue de la Houssinière, BP 32229, 44322 Nantes Cedex 3, France.
authors.forename: A
authors.identifier: http://orcid.org/0000-0001-5981-5480
authors.initials: A
authors.lastname: Lafond
authors.affiliation: Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS , 2 rue de la Houssinière, BP 32229, 44322 Nantes Cedex 3, France.
authors.forename: C
authors.initials: C
authors.lastname: Guillot-Deudon
authors.affiliation: EDF R&D, Departement EFESE, 6 Quai Watier, 78401 Chatou, France.|Institute for Research and Development of Photovoltaic Energy (IRDEP), UMR 7174 CNRS/EDF R&D/Chimie ParisTech-PSL, 6 quai Watier, 78401 Chatou, France.|Institut Photovoltaïque d'Ile-de-France (IPVF) , 8 rue de la Renaissance, 92160 Antony, France.
authors.forename: J
authors.initials: J
authors.lastname: Vidal
authors.affiliation: Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS , 2 rue de la Houssinière, BP 32229, 44322 Nantes Cedex 3, France.
authors.forename: M
authors.initials: M
authors.lastname: Paris
authors.affiliation: Laboratoire de Planétologie et Géodynamique, LPG Nantes, CNRS UMR 6112, Université de Nantes , Nantes, France.
authors.forename: C
authors.initials: C
authors.lastname: La
authors.affiliation: Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS , 2 rue de la Houssinière, BP 32229, 44322 Nantes Cedex 3, France.
authors.forename: S
authors.identifier: http://orcid.org/0000-0002-1900-0030
authors.initials: S
authors.lastname: Jobic