Thickness-dependent structural parameters of kesterite Cu2ZnSnSe4 thin films for solar cell absorbers

The influence of thickness on the structural parameters, off-stoichiometry and cation disorder in kesterite Cu2ZnSnSe4 films grown by flash deposition for solar cell absorbers is investigated employing X-ray diffraction, energy-dispersive X-ray and Raman spectroscopies. It is shown that the lattice parameters of Cu2ZnSnSe4 changed depending on film thickness: the 100 nm film turned out to be weakly stretched on the molybdenum-coated glass substrates, while, in the thicker films, the compressive deformation is defined. The causes of the changes in film structure are outlined. Raman spectra revealed secondary phases like Cu2SnSe3 detecting reduction of its fraction with an increment in thickness; also, the SnZn antisite defect fraction decreases. Simultaneously, the share of disordered kesterite phase associated with CuZn antisite defects rises with thickness. The obtained results can be useful for optimization of technological growth process.