Behaviors of Fe, Zn, and Ga Substitution in CuInS2 Nanoparticles Probed with Anomalous X-ray Diffraction

We synthesized CuInS2 nanoparticles containing up to 20% Fe, Zn, and Ga to study alloying in photovoltaic absorber materials with anomalous X-ray diffraction. The colloidal synthesis allowed for detailed analysis of complex quaternary compounds. Anomalous X-ray diffraction (AXRD) was used to clarify the elemental distribution between phases. Additionally, optical spectroscopy and X-ray diffraction were used to probe the band gap and crystal phase, respectively. Substitution of Zn into wurtzite CuInS2 produced a controllable increase in the optical band gap, whereas Ga did not substitute into wurtzite CuInS2, producing no band gap change. Secondary phase precipitation of a chalcopyrite phase was observed with Fe substitution, along with a decrease of the optical band gap. This work demonstrates progress in compositional and structural analysis of quaternary chalcogenide materials using AXRD.