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

Abstract

The Cu-dependent phase transition in polycrystalline CuGaSe 2 thin films has been studied by an electron probe micro-analyzer (EPMA) and the synchrotron x-ray diffraction method. A Cu-deficiency parameter, Z, defined as (1 À Cu/Ga) was used to study the phase transition. Upon increasing the Z-value, the composition of the films on the Cu 2 Se-Ga 2 Se 3 pseudo binary tie line was found to shift from the stoichiometric CuGaSe 2 (1:1:2) (Z ¼ 0) to the Ga-rich composition through the formation of several ordered defect compounds.The structural modification in the Cu-poor CuGaSe 2 film has been investigated by the synchrotron x-ray diffraction method. The existence of the Cu-poor surface phase over the near-stoichiometric bulk CuGaSe 2 film was confirmed by the fitting of the accelerated voltage dependent EPMA data.

Effect of Ga/Cu Ratio on Polycrystalline Thin Film Solar Cell

“…For further increase of the Ga content (e.g., Ga/Cu = 2.03), film was found to be associated with smaller grains covered with melted-like impurity phases as seen in Figure 1(a). With an increase in the bulk Ga/Cu ratio (i.e., with a decrease of Cu content) in the film above the stoichiometry, structural modification occurs which starts from the surface of the film directing along the depth of the film towards the substrates [16]. Therefore, we believe impurity phases covering the surface region of the Ga-rich films might originate from the ordered defect compounds (e.g., CuGa 3 Se 5 ) which is also known as defect chalcopyrite.…”

Deep level emission in polycrystalline CuGaSe2 thin-films observed by micro-photoluminescence

“…Detail experimental proce-dure of the three-stage method has been described before. 21) Mo back-contact layers of 800 nm thickness were deposited by sputtering method with Ar gas pressure of 0.30 Pa. Evaporation of CuGaSe 2 films was done at a base pressure of approximately ∼10 −6 Pa from three Knudsen-cells (K-cells) that were the respective Cu, Ga, and Se sources.…”

Microstructure characterization of the soda-lime-glass/copper–indium–gallium–selenium interface in Cu-poor Cu(In,Ga)Se2 thin films

“…Understanding the proper physics and growth mechanism for the OVC phase formation in CIGS material is critical for further improvements of the devices performance. A Cu-deficiency parameter, Z, defined as (1-Cu/Ga) was used to study the phase transition in CuGaSe 2 material, and a series of OVC phase formations were observed with an increasing Z-value [8]. Raman spectra intensity of the chalcopyrite Cu(In,Ga)Se 2 band progressively increases with higher Cu content (Cu/(In + Ga) ≥ 0.60), and the contribution from the OVC bands becomes negligible with higher Cu/(In + Ga) N 0.80 [9].…”