Kesterite-based solar cells are attracting considerable attention in recent years, owing to the reduced toxicity and greater abundance of their constituent elements. In this brief review, we discuss the current status of this important technology by focusing on three key aspects of the device: (i) the interface between the kesterite absorber and the Mo back contact, (ii) the kesterite absorber bulk defects and grain boundaries and (iii) the interface between the kesterite absorber and the buffer layer. By identifying key issues to be addressed, we provide suggestions for their potential improvement and future research.

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The main obstacle to widespread application of single-wall carbon nanotubes is the lack of reproducible synthesis methods of pure material. We describe a new growth method for single-wall carbon nanotubes that uses molecular beams of precursor gases that impinge on a heated substrate coated with a catalyst thin film. In this growth environment the gas and the substrate temperature are decoupled and carbon nanotube growth occurs by surface reactions without contribution from homogeneous gas-phase reactions. This controlled reaction environment revealed that SWCNT growth is a complex multicomponent reaction in which not just C, but also H, and O play a critical role. These experiments identified acetylene as a prolific direct building block for carbon network formation that is an order of magnitude more efficient than other small-molecule precursors. The molecular jet experiments show that with optimal catalyst particle size the incidence rate of acetylene molecules plays a critical role in the formation of single-wall carbon nanotubes and dense vertically aligned arrays in which they are the dominant component. The threshold for vertically aligned growth, the growth rate, the diameter, and the number of walls of the carbon nanotubes are systematically correlated with the acetylene incidence rate and the substrate temperature.

This letter reports on fast and highly anisotropic thermal transport through millimeter-tall, vertically aligned carbon nanotube arrays ͑VANTAs͒ synthesized by chemical vapor deposition on Si substrates. Thermal diffusivity measurements were performed for both longitudinal and transverse to the nanotube alignment direction, with longitudinal values as large as 2.1± 0.2 cm 2 / s and anisotropy ratios as large as 72. Longitudinal thermal conductivities of 15.3± 1.8 W / ͑m K͒ for porous 8 ± 1 vol % VANTAs in air and 5.5± 0.7 W / ͑m K͒ for epoxy-infiltrated VANTAs already exceed those of phase-changing thermal interface materials used in microelectronics. Data suggest that further improvements are possible through optimization of density and defects in the arrays.