Preparation and characterization of co-evaporated Cu2ZnGeSe4 thin films

• Synthesis of Cu2ZnGeSe4 films for solar cell absorber layer
• Effect of substrate temperature on the growth of co-evaporated Cu2ZnGeSe4 films
• X-ray diffraction, Raman and morphological studies of Cu2ZnGeSe4 thin films

Cu2ZnGeSe4 (CZGSe), a member of Cu2–II–IV–VI4 family, is a promising material for solar cell absorber layer in thin film heterojunction solar cells like Cu2ZnSnS4 and Cu2ZnSnSe4 which have been explored in recent years as alternate to CuInGaSe2 solar cells. The effect of substrate temperature (523 K–723 K) on the growth of CZGSe films is investigated by studying their structural, morphological and optical properties. Raman spectroscopy studies have been done to identify the phases in addition to X-ray diffraction studies. CZGSe films deposited at different substrate temperatures and annealed at 723 K in selenium atmosphere are Cu-rich and Ge-poor and contained secondary phases Cu(2 − x)Se and ZnSe. CZGSe films obtained by reducing the starting Cu mass by 10% were found to be single phase with stannite structure, the lattice parameters being a = 0.563 nm, c = 1.101 nm. The direct optical band gap of CZGSe films is found to be 1.63 eV which is close to ideal band gap of 1.50 eV for the highest photovoltaic conversion efficiency. The films are found to be p-type.