654_ch9 - ECE 654 Solid State Devices II Prof. S. Mohammadi...

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Unformatted text preview: ECE 654 Solid State Devices II Prof. S. Mohammadi - 143 - Chapter 9 Solar Cells In this chapter we study the basics of solar cells and their state of the art performance. It is important to realize that they are two distinctive applications for solar cells. Solar cells with high performance and high conversion efficiency characteristics are needed for space applications and satellites. These are typically single crystalline multi-junction devices that require high production costs. On the other hand, solar cells that can be mass produced in large areas and at extremely low cost are often characterized by low conversion efficiencies. These types of solar cells are implemented using thin film amorphous, poly-crystalline Si or even organic materials. Their production does not require high temperature processing, therefore, these devices can be built on flexible plastics. This enables large area and low cost production of thin film and organic solar cells. Basic Principles A solar cell is a PN junction that can be modeled according to Fig. 9.1. The model consists of a constant current source I ph , the load current I and the reverse saturation current of the diode I S . The current voltage characteristics of such a diode under illumination are also shown in Fig. 9.1. As can be seen, under illumination the device IV characteristics push to the fourth quarter, therefore the diode is capable of generating power with illumination. We shall look at the fourth quadrant more closely. Fig. 9.2. shows the I-V characteristics of an illuminated solar cell. The open circuit voltage V oc is the I R S R L I ph I S {exp(qV/KT)-1} I V Dark with illumination power can be generated in the 4 th quadrant I R S R L I ph I S {exp(qV/KT)-1} I R S R L I ph I S {exp(qV/KT)-1} I V Dark with illumination power can be generated in the 4 th quadrant Fig. 9.1: (top) Equivalent model of a solar cell. (bottom) I-V characteristics of the diode in dark and with illumination. ECE 654 Solid State Devices II Prof. S. Mohammadi - 144 - maximum voltage at the load (R L = ) and the short circuit current I SC is the maximum current through the load under short circuit condition (R L = 0). In order to achieve = 0)....
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This note was uploaded on 02/19/2012 for the course ECE 654 taught by Professor Mohammadi during the Spring '08 term at Purdue University-West Lafayette.

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654_ch9 - ECE 654 Solid State Devices II Prof. S. Mohammadi...

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