Formation of CuInSe2 films from metal sulfide and selenide precursor nanocrystals by gas-phase selenization, an in-situ XRD study.

In this work phase pure CuInSe 2 thin flms were obtained by selenization of ternary CuInSe 2 and CuInS 2 nanocrystals and mixtures of binary nanocrystals such as CuS, In 2 S 3 , Cu 2 Se and In 2 Se 3 . The temperature of the selenium source was kept at 400 °C during selenization. Monitoring the process using in-situ x-ray diffraction, the effect of selenization on the phase formation and grain growth in the precursor film was investigated. Whereas CuInSe 2 and CuInS 2 nanocrystals exhibit little grain growth, we found that mixtures of binary nanocrystals can show significant sintering depending on the reaction conditions. For the mixture of CuS and In 2 S 3 nanocrystals, the crystallinity and the morphology of the obtained fims strongly depends on the Cu/In ratio, with a Cu excess strongly promoting grain growth. With mixtures of Cu 2 Se and In 2 Se 3 nanocrystals the selenium partial pressure plays a crucial role. Selenium evaporation from the mixed compounds results in CuInSe 2 films composed of relatively small crystallites. Higher selenium partial pressures however resulted in improved sintering. Incomplete propagation of the selenization reaction through the layer was observed though, only leading to a well sintered CuInSe 2 top layer above a fine grained bottom layer. [ABSTRACT FROM AUTHOR]