Title: Investigation of Combinatorial Coevaporated Thin Film Cu2ZnSnS4. I. Temperature Effect, Crystalline Phases, Morphology, and Photoluminescence

Cu{sub 2}ZnSnS{sub 4} is a promising low-cost, nontoxic, earth-abundant absorber material for thin-film solar cell applications. In this study, combinatorial coevaporation was used to synthesize individual thin-film samples spanning a wide range of compositions at low (325 °C) and high (475 °C) temperatures. Film composition, grain morphology, crystalline-phase and photo-excitation information have been characterized by x-ray fluorescence, scanning electron microscopy, x-ray diffraction, Raman spectroscopy, and photoluminescence imaging and mapping. Highly textured columnar grain morphology is observed for film compositions along the ZnS-Cu{sub 2}ZnSnS{sub 4}-Cu{sub 2}SnS{sub 3} tie line in the quasi-ternary Cu{sub 2}S-ZnS-SnS{sub 2} phase system, and this effect is attributed tomore » structural similarity between the Cu{sub 2}ZnSnS{sub 4}, Cu{sub 2}SnS{sub 3}, and ZnS crystalline phases. At 475 °C growth temperature, Sn-S phases cannot condense because of their high vapor pressures. As a result, regions that received excess Sn flux during growth produced compositions falling along the ZnS-Cu{sub 2}ZnSnS{sub 4}-Cu{sub 2}SnS{sub 3} tie line. Room-temperature photoluminescence imaging reveals a strong correlation for these samples between film composition and photoluminescence intensity, where film regions with Cu/Sn ratios greater than ∼2 show strong photoluminescence intensity, in comparison with much weaker photoluminescence in regions that received excess Sn flux during growth or subsequent processing. The observed photoluminescence quenching in regions that received excess Sn flux is attributed to the effects of Sn-related native point defects in Cu{sub 2}ZnSnS{sub 4} on non-radiative recombination processes. Implications for processing and performance of Cu{sub 2}ZnSnS{sub 4} solar cells are discussed.« less

[ital In] [ital situ] coevaporated YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]] thin films have a slightly depressed transition temperature [ital T][sub [ital c]], though they have excellent radio-frequency surface resistance characteristics. These films consistently have less orthorhombic strain than laser ablated or post-annealed films. Low temperature (320--420 [degree]C) post-annealing of [ital in] [ital situ] coevaporated films in 100 kPa of O[sub 2] raised [ital T][sub [ital c]] to values as high as 91.5 K with some increase in the orthorhombic strain. All measured thin films show less variation of [ital T][sub [ital c]] with orthorhombic strain than does bulk material.