Quantum dot solar cells

Abstract

In this thesis, hot carrier relaxation dynamics in semiconductor quantum dots and quantum well structures have been investigated as the basis for improving on the efficiency of conventional solar cells to values between 40% and 60% beyond the Shockley and Queisser detailed balance limit of 30% hitherto. Two schemes have been employed to obtain the shift in efficiency: The first is multiple exciton generation which occurs in semiconductor quantum dots. The output current as a function of the photogenerated voltage and the material band gap, is computed from the difference between the photogenerated and the recombination currents. The output voltage is obtained from corrections made to the voltages used in the splitting of water by standard photochemical processes. The second is the formation of minibands in semiconductor quantum well structures which serve as the intermediate band required in the material bandgap in intermediate-band solar cell concept. Here, the output current is calculated from the difference between the photon flux absorbed by the cell and that emitted as a result of radiative recombination, all multiplied by a factor of the electronic charge. The output voltage is computed from the difference between the chemical potentials of the conduction and valence bands.