Exercise 8.1-3

IV Characteristics of Real Solar Cells

	Lets consider a solar cell as described in the backbone, with a built in series resistance RSE and a shunt resistance RSH
				We have the equivalent circuit diagram as shown.
				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.
				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.

	Take the following schematic curve of the I-U-characteristics as a reference and for the definition of the following terms:
		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.
				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:
					The open-circuit voltage UOC.
					The short-circuit current ISC.
					The reverse dark current if the solar cell is bisased in the reverse direction.
					The fill factor FF (the degree of "rectangularism" of the characteristics).
					The efficiency h which is proportional to UOC, ISC, and FF, i.e.
					h  =  const · UOC · ISC · FF
	Link to the solution

With frame

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)