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This is an author produced version of a paper published in Solar Energy Materials and Solar Cells. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination. AbstractWe investigate Cu(InGa)Se 2 thin films grown in multi-stage coevaporation processes and solar cells fabricated from such absorbers. Despite some interdiffusion during film growth, Ga/(Ga+In) gradients defined via evaporation-profile variations in the process are to a good part retained in the finished film. This indicates that the bandgap can be engineered in this type of process by varying the evaporation profiles, and consequently also that unintended profile variations should be noted and avoided. With front-side gradients the topmost part of many grains seems to be affected by a higher density of lattice defects due to the strong change of gallium content under copper-poor growth conditions. Electrically, both back-side gradients and moderate front-side gradients are shown to yield an improvement of device efficiency. If a front-side gradient is too wide, though, it causes strong voltage-dependent collection and the fill factor is severely reduced.

We use secondary-ion mass spectrometry (SIMS), X-ray diraction (XRD) and scanning electron microscopy (SEM) to investigate the development over time of compositional gradients in Cu(In, Ga)Se 2 thin lms grown in threestage coevaporation processes, and suggest a comprehensive model for the formation of the well-known`notch' structure. The model takes into account the need for compensating Cu diusion by movement of group-III ions in order to remain on the quasi-binary tie line and indicates that the mobilities of In and Ga ions dier. Cu diuses towards the back in the second stage and towards the front in the third, and this is the driving force for the movement of In and Ga. The [Ga]/[In + Ga] ratio then increases in the direction of the respective Cu movement because In has a higher mobility at process conditions than has Ga. Interdiusion of In and Ga can be considerable in the (In, Ga) 2 Se 3 lm of the rst stage, but seems largely to cease in CIGS and shows no signs of being boosted by the presence of a Cu 2 Se layer.

Nanostructured iron oxides, and especially hematite, are interesting for a wide range of applications ranging from gas sensors to renewable solar hydrogen production. A promising method for deposition of low-dimensional films is atomic layer deposition (ALD). Although a potent technique, ALD of ultrathin films is critically sensitive to the substrate and temperature conditions where initial formation of islands and crystallites influences the properties of the films. In this work, deposition at the border of the ALD window forming a hybrid ALD/pulsed CVD (pCVD) deposition is utilized to obtain a deposition less sensitive to the substrate. A thorough analysis of iron oxide phases formation on two different substrates, Si(100) and SiO2, was performed. Films between 3 and 50 nm were deposited and analyzed with diffraction techniques, high-resolution Raman spectroscopy, and optical spectroscopy. Below 10 nm nominal film thickness, island formation and phase dependent particle crystallization impose constraints for deposition of phase pure iron oxides on non-lattice-matching substrates. Films between 10 and 20 nm thickness on SiO2 could effectively be recrystallized into hematite whereas for the corresponding films on Si(100), no recrystallization occurred. For films thicker than 20 nm, phase pure hematite can be formed directly with ALD/pCVD with very low influence of the substrate on either Si or SiO2. For more lattice matched substrates such as SnO2:F, Raman spectroscopy indicated formation of the hematite phase already for films with 3 nm nominal thickness and clearly for 6 nm films. Analysis of the optical properties corroborated the analysis and showed a quantum confined blue-shift of the absorption edge for the thinnest films.

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