T-00134: Multi-Variable Photovoltaic Measurement System

Summary of Technology

The invention disclosure describes a new measurement system complementary to standard photovoltaic (PV) measurement systems with the goal of obtaining in depth understanding of the physical processes and properties that take part in the overall PV characteristics of materials, interfaces, and devices. The system uses time (t), temperature (T), photon flux (Φ), photovoltage (Vph), photocurrent (Iph), and illumination wavelength (λ) as the measurement variables to test PV materials and devices under variety of measurement conditions. Overall, this technology provides photovoltaic research an opportunity to obtain measurements that could help develop photovoltaics to not only meet specifications in a laboratory but also in field.

Inventor: Mahdi Farrokh Baroughi, Ph.D.

Description of Technology

The invention involves the development of a modular unit capable of conducting several important measurements related to photovoltaic materials and devices. Variables of measurement include: time, temperature, photon flux, photovoltage, photocurrent, and illumination wavelength. Some of the measurements include but not limited to:

• Photoconductivity decay(σph-t-T)
• Photovoltage decay(V-t-T)
• Photocurrent decay(I-t-T)
• Photovoltage – photon flux(V-Φ-T)
• Photocurrent– photon flux(I-Φ-T)
• Time of flight(t-T)

The results of these measurements are important to understand physical properties of PV materials and devices including lifetime of excess energy carrying particles, density and activity of defect states in the bulk of PV materials and at the PV interfaces, mobility of free carriers, and dynamic response of PV devices and photodetectors. IV measurement is not sufficient to understand physical and chemical properties associated with new photovoltaics. The proposed system provides researchers with a tool capable of combining variables in an effort to understand physical and chemical causal relationships. Measurement data, along with measurement outcomes, constitute the basis for comprehensive analysis and understanding of charge transport and energy loss mechanisms in advanced PV materials and devices.

The general trend in photovoltaics has been deviating from the use of conventional crystalline semiconductors, particularly silicon. As new materials are used, new understanding of complex material properties benefits industry. After measurements are made with the system, software within the system interprets the data and creates a tool used to display a vast spectrum of information. By measuring multiple variables and combining information, the system results in quantifiable data helpful to understand density and activity of defect states and impact on the performance characteristics of PV devices. Another benefit of this system is research standardization. Currently, research groups try to implement measurement setups individually which prevent a standardized measurement procedure necessary for research collaboration between entities. The invented measurement system provides a solution to this problem by creating standardized measurements capable of comparison between commercial entities, academic researchers, or combination thereof.

An article from the Materials Research Society Vol. 13 titled Photovoltaics Characterization: A Survey of Diagnostic Measurements written by L.L. Kazmerski depicts areas of photovoltaic technology in need of advancement. Standard evaluation of products, validation of materials and cell properties, and the engineering and documentation of the ensemble of device properties from internal interfaces through power outputs are listed. Kazmerski states, “The demands are for higher spatial resolution, higher accuracy and precision, better reproducibility, automation, and in situ analysis, ease of operation, and determination of properties that are fundamental to the optimization of materials and devices.” The SDSU system can potentially be used as a tool to understand the properties Kazmerski describes as needed for further understanding and technological development. By creating a system with such capabilities, standardization of measurements is provided for the research community to make sense of experimental data.

Market

Solar technology has experienced dramatic growth and is expected to grow exponentially to meet the need of rising fossil fuel energy costs. The Solar Energy Technologies Program, dedicated to the advancement of solar technology, has the mission to “conduct aggressive research, development, and deployment of solar energy technologies and systems to significantly reduce the cost of solar electricity by 2015.” As a whole, investors are spending more toward this field because consumer interest is seeking an alternative to current fuel sources.

Several companies currently offer photovoltaic measurement tools. Agilent is a leader in PV measurement tools. The Agilent B1500A system measures dark and illuminated IV, impedance spectroscopy, and open circuit voltage decay measurements. The B1500A system is not intended to test open circuit voltage-photon flux, short circuit current-photon flux measurements, or time-of-flight. Furthermore, measurements with the B1500A are conducted under room temperatures. The SDSU invention’s ability to test more variables with all tests having a wider temperature range shows improvement over existing technology.

Photovoltaic technologies have reached a point where solar cells need specialized measurement systems that are either being developed or not currently available. The growth of solar cell technology has presented both opportunities and challenges in testing, measurement, and other new energy components. Thus, specialized measurement systems can provide companies tools needed to advance solar technology to a point of commercial application. Agilent Technologies is active in finding solutions to problems associated with testing photovoltaic technology. Agilent has described problems such as testing not only in design environments but also volume-manufacturing environments. Improving testing and verification efficiency is a priority in their photovoltaic technology. Another company in the market of solar testing equipment is Konica Minolta Sensing Americas, Inc. A full line of photovoltaic measurement and characterization instruments were presented at the SPIE Optics and Photonics show held at San Diego in August 2010. Konica Minolta showcased a reference cell used as a standard point of calibration to ensure consistent measurements of newly developed photovoltaic cells and was shown sensitive to a greater portion of the light spectrum. Further PV Measurements, Inc in Boulder Colorado is a company focusing on selling testing equipment. The market for this product not only includes companies focusing on photovoltaic research, but other labs in academia could benefit from this measurement system.