SBIR-STTR Award

Proposed is the development of a non-contact spectral response (Quantum Efficiency) system capable of monitoring critical process parameters in the solar manufacturing line. The development will leverage Tau Science Corporations extensive experience in photovoltaic metrology and its proprietary FlashQE product line. FlashQE is an LED-based, spectral response system capable of measuring the quantum efficiency (QE) of a photovoltaic solar cell in just 1 second (compared to 5-10 minutes for a conventional QE system). Quantum efficiency provides fundamental information about the performance and characteristics of the cell such as band gap, defectivity, and coating quality. It is of particular interest for thin film technologies, proving stoichiometric information about the mix of materials deposited to build the cell. FlashQE is fast enough to sample at the rate of a modern photovoltaic manufacturing line and was developed with that purpose in mind. However, in its current configuration, the system requires that electrical contact be made with the cell, thereby limiting its use to end-of-line test when the cell has been fully formed. For maximum utility the system could be modified through the development of a non-contact current sensing probe to provide real-time, fundamental information about the solar cell in early in the manufacturing process. These data can be leveraged into improvements in the manufacturing line efficiency as an input to short-loop process control, with the sensor positioned directly after each deposition step. Such information, not currently available to manufacturer, would allow optimization of the line in real-time using the data to identify excursions based on predefined control limits. This would represent a tremendous improvement in the time-to-data for process control by providing real-time feedback rather than waiting until end-of-line to send samples for analysis. Waiting twelve hours or more to evaluate the efficacy of a process step makes it difficult to keep deposition processes within a predefined process window, and leads to larger drift in critical parameters such as film composition. This Phase I proposal seeks funding to develop a proof-of-concept prototype of a non-contact, spectral response measurement system capable of operating within the cost, throughput, and facilities constraints of a modern photovoltaic cell manufacturing line. The development will involve modification of an existing Tau Science product from being contact (requiring leads to fly to the cell) to being non-contact (using a capacitive probe or similar sensing schema). Basic characterization and noise studies will be conducted using the prototype and industry input will be sought through Tau Sciences customer contacts.

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.