Nucleation and Growth Behavior of Quaternary-Sputtered Copper Indium Gallium Diselenide Thin Films

摘要

In the past two decades, the growing global demand for solar energy has spurred scientific interest in alternative technologies to conventional silicon. In particular, CuIn_(1-x)Ga_xSe_2 (CIGS) has emerged as a competitor. We have developed a scalable deposition technique using RF magnetron sputtering of quaternary CIGS. Notably, the resulting films do not require post-selenization, reducing processing time and cost. We have fabricated devices above 10% efficiency using this approach, showing its promise as a production method for high-performance CIGS photovoltaics. However, the morphology of the sputtered CIGS layer is markedly different from conventional evaporated films; grain sizes vary through the thickness of the film, with numerous small grains dominating at the Mo/CIGS interface that then either terminate or grow in an inverted-pyramid fashion to form large, columnar grains at the CIGS/CdS interface. To better understand the origin of this morphology, we have studied the growth behavior of the CIGS layer using a combination of atomic force microscopy and electron microscopy to observe initial nucleation and grain growth behavior of quaternary-sputtered CIGS. We also discuss the effects of interfacial layers at the Mo/CIGS interface, demonstrating a novel wetting layer that conformally coats the Mo surface.