Structure, chemistry, and growth mechanisms of photovoltaic quality thin-film Cu(In,Ga)Se2 grown from a mixed-phase precursor

Abstract

The formation chemistry and growth dynamics of thin-film CuInSe2 grown by physical vapor deposition have been considered along the reaction path leading from the CuxSe:CuInSe2 two-phase region to single-phase CuInSe2. The (Cu2Se)β(CuInSe2)1−β (0<β≤1) mixed-phase precursor is created in a manner consistent with a liquid-phase assisted growth process. At substrate temperatures above 500 °C and in the presence of excess Se, the film structure is columnar through the film thickness with column diameters in the range of 2.0–5.0 μm. Films deposited on glass are described as highly oriented with nearly exclusive (112) crystalline orientation. CuInSe2:CuxSe phase separation is identified and occurs primarily normal to the substrate plane at free surfaces. Single-phase CuInSe2 is created by the conversion of the CuxSe into CuInSe2 upon exposure to In and Se activity. Noninterrupted columnar growth continues at substrate temperatures above 500 °C. The addition of In in excess of that required for conversion produces an In-rich near-surface region with a CuIn3Se5 surface chemistry. A model is developed that describes the growth process. The model provides a vision for the production of thin-film CuInSe2 in industrial scale systems. Photovoltaic devices incorporating Ga with total-area efficiencies of 14.4%–16.4% have been produced by this process and variations on this process.

Research on polycrystalline thin-film submodules based on CuInSe{sub 2} materials. Final subcontract report, 11 November 1990--30 June 1995

“…The use of thermal evaporation sources of the elements has been the most common small scale technique employed in highest quality CIGS f i l m formation and a number of deposition sequences have been reported that lead to excellent material properties of the W. [18,19] The issue here addressed at Solarex is the question of scalability of such a process. In most of the work here presented we have concentrated on a deposition schedule that can be considered semi-sequential in the sense that the indium and gallium are co-evaporated in the presence of selenium followed by deposition of copper in the presence of selenium.…”

“…On top of the CdS, a ZnO bilayer is deposited, an intrinsic ZnO layer of 50 nm, followed by a conductive ZnO layer 300 -500 nm thick. The doped ZnO layer has a typical sheet resistance of [10][11][12][13][14][15][16][17][18][19][20] ohms/sq and 88-94% integrated transmission in the visible spectra.…”

“…This problem was attacked and greatly reduced through modifkitions to the scribing processes and the associated contacting layers. This program also allowed development and scale-up of processes for the deposition of all other substrate, heterojunction buffer, and window layers and associated scribinglmodule formation operations to Cross-section scanning electron micrographs of CIGS films deposited using various methods Compositional uniformity of absorber layer over a 9" x 9" area Uniformity of device performance over a 3" substrate Uniformity of average device performance over eight 3"x3" substrates Frequency histogram of device performance on eight 3"x3" substrates Absorber layer composition for six consecutive depositions Device J-V parameters for six consecutive absorber layer depositions Measurement of J-V characteristic of a module segment either through a top grid or an interconnect A scanning electron micrograph and schematic view of step coverage of ZnO at an interconnect An optical micrograph of a defective substrate scribe An optical micrograph of a high quality substrate scribe 29 The light J-V characteristic ofthe highest efficiency small area cell 32 The dark J-V characteristic of the highest efficiency small area cell 33 A schematic representation of the circuit used for module analysis 35 Calculated and measured J-V data for a module segment using 36 various segment widths, fiont contact and interconnect resistivities The calculated module efficiency using 18 or 12 mil interconnects 37 The calculated module efficiency uSig 6 or 0 mil interconnects 38…”

Cu-dependent phase transition in polycrystalline CuGaSe2 thin films grown by three-stage process

“…Therefore, finally, at the thirdstage of the growth procedure, when this quasi-liquid phase is exposed to the Ga and Se fluxes under the environment of sufficient Se vapor pressure, it contributes to form the CuGaSe 2 film via several vapor-liquid-solid mechanisms. 25,26 This growth mechanism can explain the relatively Cu-stoichiometric composition in the bulk of the film. However, the mechanism for the Cudepleted surface formation even for the slightly Cu-rich bulk composition has not yet been understood.…”

Solar cells on CMOS chips as energy harvesters : integration and CMOS compatibility

“…5.2 shows the time-temperature profile of the three-stage co-evaporation process. Later, a lot of research studies have been done based on this process technology [167][168][169]. The CIGS efficiency approached 20% by the end of last century [170].…”