UC San Diego

At least 90% of current photo-voltaic (PV) solar cells are dominated by silicon based structures. For practical use, silicon needs to be physically processed by slicing into wafers and polished, and microscale / nanoscale geometrical changes added for circuits and devices. After the wire sawing procedure, less than 50% of the silicon feedstock ends up as useful wafers with the remaining Si material lost as sawing slurry (kerf loss). Since approximately one-half of the cost of the high-efficiency, crystalline Si solar cells is the silicon materials cost, it would be highly desirable to reduce the slicing loss and usage of Si in the solar cells. In view of the expanding needs for thin Si for variety of applications such a flexible, bendable or stretchable electronics, nanowire shaped Si for advanced PV solar cells as well as a need to produce affordable PV solar cells with substantially reduced Si materials cost, convenient direction-controllable and rapid Si shaping technique is highly desirable. We have created here a new and unique Si slicing and patterned shaping method using magnetically direction-guided etching. The method can produce very thin Si sheets or create zig-zag Si wires, with a possibility of obtaining Si wafers essentially ignoring the crystallographic preferred etch directions. The application of magnetic force and gradient field accelerates the kinetics of Si etching/slicing. The Si slicing waste during the magnetically guided slicing can be minimized to be as small as 5 um or less thickness per each Si slicing, as compared to at least an order of magnitude more loss for common mechanical slicing. These studies are discussed in chapter 2. We also described nanopatterning techniques using atomic force microscopy (AFM) based or nano-manipulator based patterning of a substrate surface using localized oxidation of nano- islands or localized changes of surface structure due to applied voltage through the tip of multi-probe. Some embodiments include the utilization of an arrayed nanoprobe for simultaneous writing of many islands or lines, followed by a pattern transfer by reactive ion etching. These studies are discussed in chapter 3