Inaug.-diss.--Berlin. / Lebenslauf.

Inaug.-Diss.--Halle-Wittenberg. / Lebenslauf. "Literatur": p. [87]-90.

Inaug.-Diss.--Landwirtschaftliche Hochschule, Berlin. / Lebenslauf. "Literaturverzeichnis": p. 5-7.

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 383-396).

Thesis (Ph. D.)--University of Wisconsin, 1964. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin-Madison, 1948. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--Ohio State University, 1974. / Bibliography: leaf 48. Available online via OhioLINK's ETD Center

Les cellules solaires à base de CuIn1-xGaxSe2 sont des dispositifs en couches minces permettant d’atteindre des hauts rendements de conversion photovoltaïque. Le CuIn1-xGaxSe2 est un absorbeur permettant d’adapter l’énergie de la bande interdite de la cellule solaire en changeant la teneur en Ga. Le rendement record de conversion photovoltaïque actuel a été obtenu pour x~0.3, alors que la théorie indique qu’il devrait être obtenu pour un x~0.7. L’origine de cette limite pour x élevé reste en débat. Dans cette thèse, on étudie deux origines liées aux interfaces internes de CuIn1-xGaxSe2 à savoir i) le changement d’élément ségrégé aux joints de grains pour des fortes et faibles teneurs en Ga et ii) la ségrégation défavorable du séléniure du cuivre au volume ou à la surface. Dans une première partie, une étude par premiers principes (DFT) montre que la ségrégation substitutionnelle de l’In par Ga (ou de Ga par In) n’est pas favorisée dans un joint de macle. Dans le cas plus général d’une surface notre étude sur les forces motrices de ségrégation montre qu’il est plus facile de faire ségréger une impureté d’In qui se trouve dans une matrice de CuGaSe2 que l’inverse. Dans la seconde partie, les résultats expérimentaux du CuIn1-xGaxSe2 indiquent qu’en augmentant le taux de Ga la couche devient plus inhomogène. Cela est dû aux inhomogénéités locales de concentration en Cu dans la couche. L’origine de ce phénomène est liée à la cinétique de la formation de CuGaSe2 qui est lente et à la faible diffusion du Cu et du Ga. Nous proposons une étape de relaxation supplémentaire pendant la co-évaporation de CuIn1-xGaxSe2 qui permet de faciliter la croissance des grains, d’améliorer l’homogénéité de la couche et d’atteindre l’équilibre attendu. / Amongst the different semiconductor materials used as absorber layers, polycrystalline CuIn1-xGaxSe2 is one of the most promising materials in the thin-film photovoltaic technology. Due to the high efficiency, stability and band gap tunability with x, thin-film solar cells based on CuIn1-xGaxSe2 absorber layer are already industrially implemented. Moreover, in the multi-junction solar cell technology the aim of reaching higher efficiencies while keeping the fabrication costs low, makes the wide band gap indium-free CuGaSe2 absorber layer an interesting candidate as a top cell in a hybrid tandem solar cell based on c-Si bottom cell. However, the actual energy conversion efficiency strongly decreases for x larger than 0.3 and it does not follow the theoretical predictions indicating better performances for x around 0.7. The difficulty to obtain a high device performance for large x has been a worldwide question for several years and many theories have been proposed to explain the limited conversion efficiency. A possible cause of the limited CuIn1-xGaxSe2 performance for large x involves the local inhomogeneities at the inter- or intra-grain regions, since the nature of the accumulated species or compound at the interfaces can be detrimental or beneficial for the solar cell efficiency. In this thesis we investigate two possible phenomena that are likely to occur at the CIGSe interfaces i) a preferential elemental segregation at the grain boundaries and ii) the detrimental copper selenide surface segregation or bulk precipitation. In this work, the elemental segregation is investigated at equilibrium by coupling ab initio calculations and thermodynamic modeling. Our results indicate that substitutional (InGa or GaIn antisite) cannot be expected in the most frequently present interfaces such as the twin grain boundaries. A complementary and simple analysis of the main segregation driving forces was also studied in order to understand the segregation in the more general cases, such as the surface segregation. Our calculations show that In is slightly more favorable to segregate at the surface rather than Ga. The experimental analysis on CuIn1-xGaxSe2 films at intermediate and large x reveals that increasing x the Cu content in the CuIn1-xGaxSe2 film can locally differ, creating detrimental Cu-enriched domains within the bulk of the film. This phenomenon is due to the slow kinetics at large x and the reduced Cu and Ga interdiffusion. In this work, we propose a strategy to avoid these local inhomogeneities by applying a relaxation stage during the CuIn1-xGaxSe2 deposition process. This stage improves the photovoltaic performance, since it leads to a long-range equilibration, grain growth, annihilation of voids and a close to stoichiometry bulk which was expected

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