G. Suresh Babu

Effect of post-deposition annealing on the growth of Cu2ZnSnSe4 thin films for a solar cell absorber layer

The effect of substrate temperature and post-deposition annealing on the growth and properties of Cu2ZnSnSe4 thin films, a potential candidate for a solar cell absorber layer, is investigated. The substrate temperature (Ts) is chosen to be in the range 523–673 K and the annealing temperature (Tpa) is kept at 723 K. Powder x-ray diffraction (XRD) patterns of as-deposited films revealed that the films deposited at Ts = 523 K and 573 K contain Cu2−xSe as a secondary phase. Single phase, polycrystalline Cu2ZnSnSe4 films are obtained at Ts = 623 K and films deposited at Ts = 673 K have ZnSe as a secondary phase along with Cu2ZnSnSe4. Direct band gap of as-deposited CZTSe films is found to lie between 1.40 eV and 1.65 eV depending on Ts. XRD patterns of post-deposition annealed films revealed that the films deposited at Ts = 523–623 K are single phase CZTSe and films deposited at Ts = 673 K still contain ZnSe secondary phase. CZTSe films are found to exhibit kesterite structure with the lattice parameters a = 0.568 nm and c = 1.136 nm. Optical absorption studies of post-deposition annealed films show that there is a slight increase in the band gap on annealing, due to decrease in the Cu content. Electrical resistivity of the films is found to lie in the range 0.02–2.6 Ω cm depending on Ts.

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

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−xSe as a secondary phase along with Cu2ZnSnSe4. Single phase, polycrystalline Cu2ZnSnSe4 films are obtained at a substrate temperature (Ts) 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 Ts.