Next Generation SLIVER Cells

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This report details the Next generation SLIVER cells project aimed to maximise the likelihood of successful commercialisation of SLIVER technology.This Next generation SLIVER cells project achieved significant improvements in SLIVER cell fabrication, demonstrating a reduction in process complexity, improved yield and substantial increases in conversion efficiency. The original goals of the project were therefore achieved however the commercial appetite for this type of technology remains to be proven.Key resultsALD deposited Aluminium oxide (Al2O3) and Titanium dioxide (TiO2)) films and film stacks behaviour proved to be highly dependent upon exact deposition conditions and subsequent anneals. Various unforeseen problems were encountered in the development of these films including problems with film blistering, conduction or current leakage through the films; film morphology / crystallography, chemical etch resistance and compatibility with other processing requirements.A larger than anticipated effort was required to arrive at a deposited film stack with all of the desired properties.Sourcing reliable n-type <110> wafers proved to be a significant problem. This type of wafer is very much a non-standard wafer type and several vendors were trialled before satisfactory material was available to the project. High efficiency cell fabrication relies upon high quality material, and effective development of processes also relies upon consistent and highly-reliable material. The first 2 vendors used supplied poor quality and highly inconsistent wafer stock for the project.SLIVER cell fabrication, laser doping and its application in particular; proved to be difficult. Several avenues for a suitable method for depositing a dopant precursor film on grooved sliver wafers were investigated with limited success. Laser doping trials revealed that, at laser settings appropriate for doping on planar silicon surfaces, the laser interaction at the corners of Sliver cell precursors resulted in significant damage and silicon removal extending some distance from the sliver corners.Many of the new approaches developed for this project are specific to the Sliver technology, and as such are not easily and directly transferable to other projects.

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