Growth and characterization of co-evaporated Cu2ZnSnSe4 thin films for photovoltaic applications

Abstract

Cu2ZnSnSe4 thin films are deposited using the four-source co-evaporation technique onto glass substrates held at 523, 573, 623 and 673 K and in situ annealed 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 Cu2−x Se as a secondary phase along with Cu2ZnSnSe4. Single phase, polycrystalline Cu2ZnSnSe4 films are obtained at a substrate temperature (T s) of 623 K on in situ annealing at 723 K. The structure is found to be kesterite and the lattice parameters are a = 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 on T s.