The objective of this work is to demonstrate a new Lehighton Electronics, Inc. (LEI) measurement technology that has high sensitivity to determine process deviations that may take place during the production of multicrystalline solar cells. The new technology measures a non-contact open-circuit voltage (OCV) response from the underlying device structure. Eddy current measurements in a solar cell can measure the resistivity or dopant density to test for uniformity. However, because of the current in the coil of the tool, detection is limited to the penetration depth of eddy currents and for a solar cell, the equipment measures the total thickness of the silicon wafer. The new OCV-based technology can measure various depths into the wafer by varying the wavelength of the illumination source. By combining OCV with eddy current measurements, a diagnostic mode is realized by making the technique more quantitative. Fifty-five data points are measured on each solar cell in a non-disruptive test that takes 2.5 minutes to complete. Wafers can be measured non-destructively at different points in the production process, namely Wafers after texturization, Wafers after diffusion, Wafers with the anti-refection coating, silicon nitride (labeled AR Coating, Wafers with finished cells, Wafers with nanostructured coatings as efficiency enhancements. This research will focus on the application of LEI legacy metrology as well as newer photovoltaic-based instrumentation toward improvements in (1) material coatings that will absorb a broader range of the solar spectrum, (2) improvements in control of the material dopants used to create the p-n junction, responsible for separating photo-generated electron-hole pairs, (3) a reduction in p-n junction-based charge carrier killing material defects and impurities, and (4) a reduction of yield degrading mechanical defects. Once sensitivity to these applications is well understood, a cost effective process control-based version of these systems will be implemented, allowing for the process control of the PV module manufacturing process. This research will lead to cost reductions in PV module manufacturing processes by defining semiconducting materials with fewer variations in defects and impurities, which typically reduce solar cell device efficiency and lead to rejected material in the manufacturing process. Lower performing modules are typically sold at a lower price; quite often, material defects and impurities brought about by poorly controlled processing are responsible. Additionally, large scale mechanical defects can lead to panel cracks and breakage, resulting in reduced yield. By detecting the presence and cause of mechanical defects early on in the process, an improvement in cost savings can be realized. The end product will be an instrument based on compact gantry mounted X, Y, Z positioning that can be mounted above a conveyor with a footprint of 24 x 24 inches - less than competitive measurement systems that occupy floor space adjacent to existing module processing equipment. This instrument, with an approximate cost of $200, 000, will produce high speed measurements used to detect out-of-bound processing conditions. Additionally, contour and surface profile maps will be generated through a slower but more informative diagnostics mode, providing more information toward the identification and quantification of the responsible agent or causation.
