Self-aligned metallization and reactive ion etched buried base contact solar cells

Damage-free reactive ion etch processes have been developed that allow the formation of grooves with intentional under-etching of the mask, e.g. photo resist. In a succeeding metal evaporation step this very same mask obstructs the deposition of metal such that the metal is only deposited on the bottom of the groove. In a lift-off process the surplus metal is removed from the wafer surface. This metallization technique allows simple fabrication of single-side contacted solar cells. It has been used to form a buried base contact through the homogeneous emitter of a rear contact solar cell. Only one mask was used to define emitter and base areas and to contact the base. After depositing the metal on the bottom of the groove, it was electroplated. No significant shunts, i.e. no short circuits between emitter and base, are observed even though during electroplating the metal has grown out of the grooves. This rear contact solar cell with buried-base contacts achieves an efficiency of 16·3% under front side illumination (neither n⁺⁺ nor p⁺⁺ doping under the contact fingers). The cell still lacks open-circuit voltage (595 mV) and fill factor (70·9%), probably due to the lack of side-wall passivation in the grooves and of a sealing of the open pn-junction. Copyright © 1999 John Wiley & Sons, Ltd.     

Metal–Matrix Composites from High-Pressure Torsion with Functionalized Material Behavior

In composites, outstanding properties of two materials can be combined. In particular, metal–matrix composites (MMCs) can combine the properties of a high-strength ductile metallic matrix with special properties of embedded ceramic particles. This hybrid can be used to create a functional material. However, during consolidation, the thermal load of most common MMC-processing routes is an obstacle for such functionalization, because the unique properties of the ceramic phases most likely degrade. Mechanical alloying, in this case, by high-pressure torsion (HPT), can overcome this challenge. Herein, the attempt to obtain smart materials through HPT processing is aimed. For that purpose, Cu-MMCs are produced from mixed powders with ${\text{ZrO}}_2$ and ${\text{BaTiO}}_3$ (BTO) with the challenge to incorporate their functional phase. BTO can provide a sensing ability for internal stress and ${\text{ZrO}}_2$ can provide a fatigue lifetime by a retarded crack growth. The amount of the stabilized phase is evaluated by X-ray diffraction. Cu–BTO–MMCs exhibit a local piezoelectric effect when strained, shown by in situ scanning Kelvin probe force microscopy. Cu–${\text{ZrO}}_2$–MMCs feature a retarded fatigue crack initiation and an earlier crack closure during fatigue crack growth due to the volume expansion once ${\text{ZrO}}_2$ transforms.     

How Hydrogen Affects the Formation and Evolution of Persistent Slip Bands in High-Purity α-Iron

The effect of hydrogen on the fatigue behavior of materials has been studied extensively during the past 100 years, but is just poorly understood due to the complex interplay between hydrogen and deformation processes. In this context, hydrogen damage of metals is becoming one of the major challenges of decarbonization. While most work focuses on f.c.c. materials, the availability of relevant results becomes sparse when considering technologically highly relevant b.c.c. metals such as structural steels. This work uses in situ electrochemical hydrogen charging of α-iron steels to investigate the formation and evolution of intrusions and extrusions prior to fatigue crack initiation using a new charging setup by which the specimens are charged from the interior. The advantage of this innovative technique is that the surface of the specimens can subsequently be characterized using atomic force microscopy without artefacts from electrochemical charging or corrosion. Hydrogen is shown to enhance slip localization at the early stages of damage. The developed persistent slip lines are less pronounced. By means of transmission Kikuchi diffraction, it is shown that orientation gradients between cells in the dislocation structure are much weaker in the presence of hydrogen. Hence, hydrogen appears to promote slip reversibility in b.c.c. materials.