# 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)