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Session Number: 3659

Solar Simulator and I-V Measurement System For Large Area Solar Cell Testing

M.G. Guvench, C. Gurcan*, K. Durgin and D. MacDonald* University of Southern Maine and *National Semiconductor, S.Portland

Abstract

This paper describes the design, operation and use of a PC controlled test setup designed specifically to measure the I-V characteristics of large area solar cells operated under simulated solar irradiation for the purpose of testing their quality and determining their optimal operational points for maximum electrical output. The project included design of a wafer-prober and solar-simulator combination so that large area wafers (up to 8 inch in diameter) could be tested at/up to AM1.5 standard solar insolation. Rather than simply looking at the short circuit current and the open circuit voltage of a solar cell, our system measures its full I-V characteristics while the cell is irradiated with an artificial light source which simulates the solar radiation. The artificial sunlight is created by combining metal-halide and quartz halogen light sources. The measurement is done in an automated way by employing standard bench top GPIB instruments interfaced to a PC and by using the function generator as a stepped voltage source. High test currents needed by the large area solar cell are provided by a unity gain DC power amplifier driven by the function generator. A Mathematica code written creates plots of measured I-V data and determines the maximum electrical power output of the cell as well as the series resistance, the parasitic effect most effective in lowering maximum power and efficiency.

1. Introduction

This project was inspired by a university-industry cooperation project between National Semiconductor Corporation and the University of Southern Maine to recycle industrial byproducts into useful devices, namely, Silicon wafers which have been used as test wafers in production lines into solar cells. The size of the Silicon wafers used in the fabrication of modern day integrated circuits is greater than 6 inches (=150 mm), typically 8 inches (=200 mm). Considering a solar intensity of 100 mW/cm2 (approximately AM1.5 conditions) an average Silicon solar cell is expected to generate more than 20 mA/cm2. [Ref. 1, 2, 3]. If a whole 8-inch wafer is turned into one single solar cell, it should generate more than 6 Amps of photo current. At such high current levels the voltage burden of a DC ammeter runs close to 300 mV, i.e. about 65% of the cell's voltage (which runs at about 450 mV), making a direct short circuit current measurement highly inaccurate if not impossible. Besides, the short circuit current of a solar cell alone is not enough to determine the cell’s power delivering capability. The maximum power delivered is also dependent on the internal voltage drops caused by the internal series resistances of the cell. There is an optimum point of operation on the I-V characteristics of the cell which needs to be determined in order to extract solar generated electrical power most efficiently. For this reason, a complete I-V characterization of the cell is needed covering the full range of operation at high current levels. This involves applying a stepped voltage and measuring the cell’s current at each step. True short circuit current can then be extracted from the plots of the I-V data at the zero volt point. Such a complete I-V measurement would also reveal the solar cell’s open circuit voltage and allow a plot of its electrical power output to be made as a function of its operating voltage, and therefore, help determine its optimum operating point for maximum possible power extraction. Having full I-V data would also help to extract parameters such as the internal series resistance, and therefore, provide feedback to the device designer to do a fine tuning of both the doping profiles and the metallization pattern design of the cell for optimization.

“Proceedings of the 2004 American Society for Engineering Education Annual Conference & Exposition Copyright © 2004, American Society for Engineering Education"

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Guvench, M. (2004, June), Solar Simulator And I V Measurement System For Large Area Solar Cell Testing Paper presented at 2004 Annual Conference, Salt Lake City, Utah. 10.18260/1-2--13121