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• In-situ AgBr treatment used to deposit homogeneous CuGaSe 2 material. • CuGaSe 2 deposition time reduced by nearly half. • Higher and more consistent open-circuit voltage and fill factor for devices. Homogeneous CuGaSe 2 thin film growth is limited by slow kinetics of formation. A modified growth process was previously developed to address this issue but requires two separate long, high temperature anneals. Here, we demonstrate that a short AgBr treatment can replace this modified growth process. The AgBr works as a transport agent to catalyze CuGaSe 2 formation and atomic mobility. This treatment results in large grains with homogeneous composition through the bulk. Solar cells made with this material show better performance. [ABSTRACT FROM AUTHOR]

• Detrimental Cu δ Se phases precipitate within the bulk of Ga-rich CuIn 1-x Ga x Se 2. • Cu δ Se bulk precipitation in the Ga-rich CuIn 1-x Ga x Se 2 films is a kinetic issue. • A relaxation stage is necessary to make the Cu δ Se segregate at the surface. • The Cu δ Se has a preferential orientation to segregate. In this paper, we propose a possible explanation of the limited CuIn 1-x Ga x Se 2 (CIGSe) performance at high Ga contents, related to the properties of detrimental copper selenide (Cu δ Se) secondary phases. We study CIGSe layers at different x, by means of X-ray diffraction analyses, Raman and energy dispersive X-ray spectroscopy. Our results reveal that for high Ga contents, Cu δ Se secondary phases either precipitate at the interfaces between grains or remain within the layer as intra- or inter-grain clusters, deteriorating the electronic properties of the absorber layer. On the contrary, for low Ga contents, the copper selenide segregates at the surface of the CIGSe and hence it can be easily removed by KCN surface etching. To understand the Cu δ Se precipitation within the bulk of the film for a high Ga ratio, we also investigate In-free CGSe samples at low and high Cu content. Our observations demonstrate that i) Cu δ Se has a preferential grain orientation to segregate and ii) the Cu-enriched regions within the bulk of the high Ga content films are more a kinetic than a thermodynamic issue. [ABSTRACT FROM AUTHOR]

• Regular CuPRO process leads to an inhomogeneous CuGaSe 2 (CGSe) layer. • Applying relaxation stages during the growth yields to a homogeneous absorber. • The relaxation stages improve the solar cell performance. • Raman analysis can be used to study chemical variations throughout the CGSe film. The present study deals with CuGaSe 2 -thin-films for solar cell applications. With the aim of achieving chemically and structurally homogeneous CuGaSe 2 layers, it is proposed a modified co-evaporation process, which implies two so-called relaxation sequences during films growth. The resulting layers are characterized by scanning electron microscopy and Raman spectroscopy. By comparing their characteristics with those of CuGaSe 2 grown without relaxation sequence, it is demonstrated that the modified process yields improved distribution of elements throughout the whole layer. The performance of the resulting solar cells is improved exclusively through increased quantum efficiency in the large wavelengths; further output voltage increase would require alternative junction partners. [ABSTRACT FROM AUTHOR]

In this study, the epitaxial growth of co-evaporated Cu(In,Ga)Se 2 films (CIGSe) onto GaP/Si(001) pseudo-substrates, where the GaP thin layer is epitaxially grown by Molecular Beam Epitaxy (MBE), is investigated. Extensive structural characterisation of epi-CIGSe is carried out via X-ray diffraction as well as transmission electron microscopy. Sturdy evidence of an epitaxial growth of CIGSe on (GaP/Si)(001) is observed, with the propagation of twins originating from the GaP/Si interface, through the CIGSe/GaP interface. This work aims at paving the way for future CIGSe/GaP/Si structures for the development of tandem solar cells with a c-Si bottom cell, and a GaP interfacial buffer layer for band edge engineering, allowing for the monolithic epitaxial growth of high quality CIGSe as a thin film top cell absorber. [Display omitted] • First report on wide bandgap CuIn 0.1 Ga 0.9 Se 2 epitaxial growth onto GaP/Si(001) pseudo-substrate. • First step for perspectives of tandem devices based on CIGSe/c-Si technologies. • Propagation of crystalline defects from the pseudo-substrate throughout the epilayer. [ABSTRACT FROM AUTHOR]