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Lets consider a solar cell as described in the backbone, with a built in series resistance RSE and a shunt resistance RSH | ||||
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We have the equivalent circuit diagram as shown. | |||
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The shunt resistance takes into account that the huge area of the pn-junction of a solar cell might have weak points (locally, e.g. at the edge) which short-circuits the junction somewhat. These defects are summarily described by a shunt resistor. | ||||
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The constant current source mimics the current generated in the junction by light. It simply defines a current value IPh (not to be mixed up with the terminal current I) that is given by the light and added (with a negative sign) to the junction current, i.e. Ijunct = Idiode(U) – IPh. The photo currentIPh thus simply moves the total characteristics of the diode downwards on the current scale. | ||||
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Take the following schematic curve of the I-U-characteristics as a reference and for the definition of the following terms: | |||||||
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The fill factor is the relation between the area of the large yellow rectangle to the more orange area centered at the optimal working point. | |||||||
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Discuss qualitatively the influence of the two resistors (and, as a more minor point, the idealiy factor n) on the IV characteristics with particular respect to: | ||||||
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The open-circuit voltage UOC. | |||||||
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The short-circuit current ISC. | |||||||
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The reverse dark current if the solar cell is bisased in the reverse direction. | |||||||
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The fill factor FF (the degree of "rectangularism" of the characteristics). | |||||||
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The efficiency h which is proportional to UOC, ISC, and FF, i.e. | |||||||
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Link to the solution |
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8.1.2 Solar Cell Current-Voltage Characteristics and Equivalent Circuit Diagram
Solution to Exercise 8.1-3: Characteristics of Real Solar Cells
© H. Föll (Semiconductor Technology - Script)