Growth and characterization of co-evaporated Cu2ZnSnSe4thin films for photovoltaic applications

Abstract

Cu₂ZnSnSe₄thin films are deposited using the four-source co-evaporation technique onto glass substrates held at 523, 573, 623 and 673 K andin situannealed at 723 K for 1 h in a selenium atmosphere. XRD studies revealed that the films deposited at 523 and 573 K and annealed at 723 K contain ZnSe as a secondary phase. However, films deposited at 673 K and annealed at 723 K have Cu_2−xSe as a secondary phase along with Cu₂ZnSnSe₄. Single phase, polycrystalline Cu₂ZnSnSe₄films are obtained at a substrate temperature (T_s) of 623 K onin situannealing at 723 K. The structure is found to be kesterite and the lattice parameters area= 0.569 nm,c= 1.141 nm. The direct optical band gap of the films is found to lie between 1.42 and 1.57 eV for films deposited at different substrate temperatures. Electrical resistivity of the films is in the range 0.1–0.8 Ω cm depending onT_s.