Organic Semiconductor (EE430.859) 2014. 6. 10.
Name	Department

* Write the answer in either Korean or English.

1. (20 point) (1) Calculate the quantized energy levels [eqn: E _{n}] and the corresponding wavefunctions [eqn: psi _{n} (x)] for an electron confined in the 1-dimensional infinite potential well as shown below:

(2) Using the energy levels [eqn: E _{n}], explain that energy gap of the quantum dot (QD) changes with the QD size.

2. (20 point)

(1) Calculate the Bohr radius of an exciton using the Bohr’s hydrogen atom model.

(2) Explain the quantum confinement effect for the semiconductor quantum dots.

3. (20 point)

(1) Draw the structure of core@shell colloidal quantum dots and explain briefly the main role of core, shell and ligand.

(2) Explain the stages of nucleation and growth for the preparation of colloidal quantum dots in the framework of the La Mer model.

4. (30 point)

(1) Draw the device structure of the quantum dot light emitting diode (QLED) and explain briefly its operation mechanism.

(2) Explain the several problems that are responsible for the poor efficiency of QLEDs.

(3) It is known that the efficiency of QLEDs rolls off at high current density due to the Auger recombination. Explain the Auger recombination mechanism and suggest the ways to overcome such problem.

5. (10 point) Compare the advantages and disadvantages of of QLEDs to those of organic light emitting diodes  (OLED).