# Exercise 8.1-1

## Quick Questions to

### 8.1 Solar Cells - General Concerns

| Here are some quick questions
|  | Give some rough numbers (with some reasoning whereever applicable), always per m2, for Maximum solar power. Maximum and practical efficiency of "standard" Si solar cells. Average power for "standard" Si solar cell. Average energy harvest of "standard" Si solar cells per year.
|  | Compare indirect and direct semiconductors with respect to light absorption at the "band edge", i.e. for light energies around bandgap energy. What follows for solar cells?
|  | What is your first priority with respect to the coupling of light and semiconductor when you want to make a solar cell with a good efficiency?
|  | Draw the current density (j) - voltage (U) characteristics of a pn-junction in the dark and under illumination in the interesting part of the j-U plot. Point out the important points of the illuminated diagram and give some approximate numbers for typical intense sun light.
|  | The typical j-U equation for a Si pn-junction is
j = | j1 | · | æ ç è | exp | eU kT | – 1 | ö ÷ ø | + | j2 | æ ç è | exp | eU 2kT | – 1 | ö ÷ ø | – jPh
|  | Discuss the origin of the j terms. Compare (qualitatively) the magnitude of j1 and j2 . What kind of properties of Si influence the value of jPh?
|  | Why is "dirty" Si not good for solar cells? Hint: Follow the fate of a photon-generated carrier.
|  | Draw the j-U curve of an illuminated decent solar cell. Draw (qualitatively) the power curve into this diagram. Discuss the curve shortly with respect to real power applications
|  | Your electrical energy bill shows that you, personally, consumed 2 000 kWh electrical energy per year in your home. How man square meters of solar cells (roughly) would you need on your roof to supply this much energy?
|  | Give the eqivalent circuit diagram of a realistic Si solar cell. Discuss the components with the aid of schematic IV-characteristics.
|  | Define the fill factor of a solar cell and discuss its dependence on solar cell parameters.

With frame

8.1.3 Summary to: 8.1 Solar Cells - General Concerns

© H. Föll (Semiconductor Technology - Script)