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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]

The impact of moisture ingress on the surface of copper indium gallium diselenide (CIGS) solar cells was studied. While industry-scale modules are encapsulated in specialized polymers and glass, over time, the glass can break and the encapsulant can degrade. During such conditions, water can potentially degrade the interior layers and decrease performance. The first layer the water will come in contact with is the transparent conductive oxide (TCO) layer. To simulate the impact of this moisture ingress, complete devices were immersed in deionized water. To identify the potential sources of degradation, a common window layer for CIGS devices—a bilayer of intrinsic zinc oxide (i-ZnO) and conductive indium tin oxide (ITO)—was deposited. The thin films were then analyzed both pre and post water soaking. To determine the extent of ingress, dynamic secondary ion mass spectroscopy (SIMS) was performed on completed devices to analyze impurity diffusion (predominantly sodium and potassium) in the devices. The results were compared to device measurements, and indicated a degradation of device efficiency (mostly fill factor, contrary to previous studies), potentially due to a modification of the alkali profile. [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]