Apparatus for Optimizing Photovoltaic Solar Manufacturing Efficiency through Real-Time Process Feedback and Spectral Binning of Cells

Novel, inline measurement techniques are needed to improve the quality and performance of new solar cells. Manufacturers today measure cell performance inline under white light conditions, but are unable to obtain the cell response as a function of wavelength without extensive offline testing. They are also unable to extract detailed spatial maps of full-spectrum spectral response. This information is fundamental to the device performance and, as device complexity increases it becomes even more important for successful process control, yield management and module power optimization. This project helps to support the nations long-term energy goal of building higher performance, consistently robust solar devices at a lower cost to the end user. Our phase I/phase II project is to develop the individual components needed for a new class of non- contact solar cell metrology, and then integrate them, by the end of phase II, into a fully functioning prototype at a major U.S. manufacturer. In phase I, we developed prototype non-contact sensors and integrated them with an advanced broadband lightsource. The lightsource has 64 colors, individually modulated, to simultaneously stimulate cell response from the ultraviolet to infrared. The response is detected via fourier analysis in one of three ways: 1) capacitive, non-contact sensors, 2) inductive non-contact sensors and 3) conventional metal contacts. The full-spectrum measurement is completed in one second, and thus is fast enough to be used as an inline process monitor. The non-contact methods show good correlation with the contacting method, and are able to detect subtle shifts in photoresponse long before the device is completed. The resulting system was tested on both conventional and thinfilm cells, as well as high performance interdigitated back contact cells. Various sensor configurations were developed and used to measure as early as the emitter formation step, and as late as a fully encapsulated module. In phase II, we will integrate the various sensors into an automated scanning system. This will be tested at a customer site on mini-modules, cells and films, and will be upgraded as the project continues. Components will be developed that lead to both higher performance and the ability to measure a broader set of materials and process steps. We will use the feedback and learning from this prototype to define the phase III product. Commercial Applications and Other Benefits: 1) module scanner for failure analysis, 2) cell spectral sorting, 3) inline monitor for absorber/emitter quality, 4) substrate contamination and surface preparation control.