S2 Films Research Articles

Fabrication of CIGS thin films by using spray pyrolysis and post-selenization

We fabricated Cu(In1−x Ga x )Se2 (x: 0 ∼ 0.4) thin films by using ultrasonic spray pyrolysis and post-selenization. First, we made Cu(In1−x Ga x )S2 (x: 0 ∼ 0.4) films by ultrasonic spray pyrolysis under an air environment. Then, we converted as-sprayed Cu(In1−x Ga x )S2 (CIGS) films to Cu-(In1−x Ga x )Se2 (CIGSe) films through post-selenization. For all Ga fractions, the sprayed CIGS films were well recrystallized into poly-crystalline CIGSe films with a dominant (112) texture, which was confirmed by X-ray diffraction, Raman spectroscopy and energy dispersive X-ray analyses. This result indicates that CIGSe films with any amount of Ga substitution can be made by converting sprayed CIGS to CIGSe with post-selenization.

In and Ga diffusion in Cu(In, Ga)Se2 and Cu(In, Ga)S2 films instantaneously prepared in a non-vacuum process

When Cu(In,Ga)(S,Se)2 is prepared by heating metal precursor films in chalcogen atmosphere (sequential process) the resulting films typically show a gradient in the Ga/(In+Ga) ratio over the depth of the film. This is generally observed for reaction periods ranging from a few minutes (rapid thermal processing) to several hours. In this work we have investigated the Ga distribution in films where the reaction period was reduced to one second. The ultra-fast reaction was achieved by passing a high electrical current through the Mo foil substrate after depositing metal and chalcogen precursors.

Cu(In,Ga)S2 films prepared by two‐stage evaporation on ZnO coated substrates

AbstractWe have prepared Cu(In,Ga)S2 films with an almost homogeneous Ga depth distribution using the two‐stage multi‐source evaporation process on soda lime glass (SLG) substrates with one of three different kinds of back contact: Mo(1000nm), ZnO(500nm), and Mo(30nm)/ZnO(500nm), respectively. We have investigated the depth profiles of Zn and Na (diffused from SLG) in Cu(In,Ga)S2 films by secondary ion mass spectroscopy (SIMS) and compare them to those in films prepared by single stage co‐evaporation. The efficiencies are higher on Mo/ZnO than they are on ZnO. It was observed by SIMS that the amount of Zn in Cu(In,Ga)S2 on Mo/ZnO is lower than it is in Cu(In,Ga)S2 on ZnO. The obtained efficiencies are generally higher with two‐stage evaporation than with single stage co‐evaporation. The Na concentration in Cu(In,Ga)S2 prepared by two‐stage evaporation is two orders of magnitude higher than in single stage co‐evaporated films. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Surface microstructure and morphology study of thin films produced from volatile fluorine-containing rare-earth β-diketonate complexes and their adducts

We present the results of a surface microstructure and morphology study of thin films produced from volatile fluorine-containing rare-earth β-diketonate complexes and their adducts. Films 0.2–0.4 μm in thickness were synthesized in vacuum by means of thermal deposition of the parent substances at a pressure of 5 × 10−4−1 × 10−3 Pa and a deposition rate of 3 × 10−3 μm s−1 (for NaNd(FOD)4 films, the deposition rate was 8 × 10−2 μm s−1). The microstructure of films depends on the deposition conditions. The films of [NaNd(PTFA)4] and [NaNd(FOD)4] complexes and Ln(PTFA)3 · S1 adducts have an amorphous structure. The [NaNd(PTFA)4(Phen)] and Nd(PTFA)3 · S2 films are characterized by a more ordered polycrystalline structure with the grain size ranging from 0.2 to 1.5 μm.

Incongruent reaction of Cu–(InGa) intermetallic precursors in H2Se and H2S

The reaction pathways to form Cu(InGa)Se2 or Cu(InGa)S2 films at 450°C from metallic precursors were evaluated by reacting Cu–In–Ga films in H2Se or H2S for 10, 30, or 90min and characterizing the phase composition of the resulting films. A starting composition comprising Cu9(In0.64Ga0.36)4 and In phases was detected by x-ray diffraction in Cu–Ga–In precursors annealed at 450°C in an Ar atmosphere. When the precursors were reacted in H2Se, a graded Cu(InGa)Se2 film was formed with a Ga-rich composition and residual Cu–Ga intermetallics at the interface with the Mo back contact. The intermetallic compounds were observed to evolve from Cu9(In0.64Ga0.36)4 to Cu9Ga4 with increasing selenization time. Reaction in H2S formed inhomogeneous Cu(InGa)S2 with Cu–In intermetallics. The results are consistent with thermochemical predictions of the preferential reaction of In with Se, and Ga with S. These reaction preferences can explain the formation of a graded Cu(InGa)Se2 film during reaction in H2Se and provide a refined understanding of the reaction sequence in two-step H2Se∕H2S processes.

Electric properties of Cu‐poor and Cu‐rich Cu(In,Ga)S 2 films after O 2 ‐annealing

We compare the fundamental electric properties of Cu-poor and Cu-rich Cu(In,Ga)S2 films before and after annealing, respectively. It has been found that the hole density of Cu-poor films increases after annealing in a O2+S combined atmosphere, whereas annealing in S only does not produce a significant effect. We conclude that the oxygen is effective for the passivation of donor-type defects in the Cu-poor Cu(In,Ga)S2 films. In the case of Cu-rich films, the hole density also increases with O2+S-annealing. However, annealing in sulphur atmosphere (no oxygen gas) in this case has comparable consequences. These observations suggest fundamental differences in the incorporation mechanisms of oxygen and sulphur in both types of the film. A tentative model is presented, taking into account results from micro-structural characterization of the films. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Cu(In,Ga)S2 Phase Formation from Metallic Cu-In-Ga Precursor Stacks in Rapid Thermal Processes

ABSTRACTThis contribution compares the growth of Cu(Ga,In)S2 based thin film solar cell absorbers in rapid thermal systems using sulfur vapor Sx or H2S/Ar as reactive atmosphere, focusing on Ga-related influences on film growth and phase formation. Cu-In alloying in the precursor is kinetically hindered by the presence of Cu-Ga phases. In sulfur vapor Ga-containing samples sulfurize via an intermediate CuIn2S8 phase, thereby delaying the full sulfurization and recrystallization of the layer. In contrast, in H2S/Ar fast Ga-In interdiffusion and no intermediate chalcogenide phases are observed. The inhomogeneous Ga depth distribution usually reported for sequentially prepared Cu(In,Ga)S2 films can be assigned to the segregation of CuGaS2 prior to CuInS2.