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• InCl 3 used to recrystallize Cu(In,Ga)Se 2 films at low temperature. • Large grains are obtained for temperature as low as 450 °C. • The films become overall indium rich with an indium rich surface. • The alkali profile is modified. One of the key challenges to promote the economic viability of Cu(In,Ga)Se 2 (CIGS) solar cells is the multi-stage co-evaporation process required to make a high quality absorber layer. One phenomenon of interest is dynamic recrystallization using a fluxing agent. While these techniques have significantly improved material systems like CdTe, their impact on other nonmetallic systems are relatively unexplored. In this paper, we demonstrate that InCl 3 can be used effectively to recrystallize CIGS for temperature as low as 450 °C, but that it also induces a modification of the surface composition. Analyses, notably via glancing incidence X-ray diffraction and secondary ion mass spectrometry, show an indium enriched surface as well as a modified alkali profile. [ABSTRACT FROM AUTHOR]

Cu(In,Ga)Se2 (or CIGS) thin films and devices were fabricated using a modified three-stage process. Using high deposition rates and a low temperature during the process, a copper chloride vapor treatment was introduced in between the second and third stages to enhance the films properties. X-ray diffraction and scanning electron microscopy demonstrate that drastic changes occur after this recrystallization process, yielding films with much larger grains. Secondary ion mass spectrometry shows that the depth profile of many elements is not modified (such as Cu, In and Se) while others change dramatically (such as Ga and Na). Because of the competing effects of these changes, not all parameters of the solar cells are enhanced, yielding an increase of 15% in the device efficiency at the most. [ABSTRACT FROM AUTHOR]

In this work, the diffusion process of sodium (Na) in molybdenum (Mo) thin films while it was deposited on soda lime glass (SLG) was studied. A small amount of oxygen was present in the chamber while the direct-current (DC) magnetron sputtering was used for the deposition. The substrate temperatures were varied to observe its effect. Such molybdenum films, with or without oxidations, are often used in thin film solar cells, either as back contact or as hole transport layers. Secondary ion mass spectrometry (SIMS) was used to quantify the concentration of the species. A grain diffusion mechanistic model incorporating the effect of grain and grain boundary geometrical shape and size was developed. The model was used to provide an in-depth theoretical analysis of the sodium diffusion in molybdenum thin films that lead to the measured SIMS data. It was observed that not only diffusion coefficients should be considered when analyzing diffusion processes in thin films but also the ratio of grain boundary size to grain size. Both depend on substrate temperature and directly affect the amount of diffused species in the film. The data were analyzed under the light of the film growth speed versus diffusion front speed, the effect of oxygen content, and the effect of substrate temperature on the overall diffusion process. The temperature inversely affects the ratio of grain boundary size and grain size and directly affects the diffusion coefficient, which leads to a preferable temperature at which the highest amount of alkali can be found in the film. [ABSTRACT FROM AUTHOR]

Using thermal evaporation, Cu(In,Ga)Se 2 (CIGS) layers were deposited at low temperature (350 °C) and high rate (10 μm/h) using a single stage process. They were then recrystallized using a variety of alkali fluorides: NaF, KF, RbF and CsF. To ensure that the substrate would not influence the study (via alkali diffusion), the samples were deposited on silicon wafers. The chemical, physical and electrical properties of the films were then characterized, demonstrating that all alkali fluorides behave as fluxing agents to enhance recrystallization and conductivity, and induce a (112) preferential orientation. Secondary ion mass spectrometry analysis showed that no modification of the elements' distribution occurs because of recrystallization. Solar cells were also fabricated and characterized, indicating that NaF can double the efficiency of solar cells compared to the as-deposited layers. This enhancement is accompanied by the disappearance of a rollover, voltage dependent current collection and shunt from the current density-voltage curves. However, even for the best recrystallization, the current is still limited to 28 mA/cm2, indicating that only a portion (0.75 μm) of the full device (2 μm) is activated. • Cu (In,Ga)Se 2 layers are recrystallized using a variety of alkali fluorides. • Efficiency of device was doubled for samples recrystallized with NaF. • Observed disappearance of rollover and shunt from the J-V curves [ABSTRACT FROM AUTHOR]