Browsing by Author "Kechiyants, H. M."

Now showing 1 - 2 of 2

Band alignment and conversion efficiency in Si/Ge type-II quantum dot intermediate band solar cells
(2007-10-10)
Kechiantz, A. M.
;
Kocharyan, L. M.
;
Kechiyants, H. M.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
The concept of the intermediate band (IB) solar cells (SC) offers the promise of achieving 63% conversion efficiency devices. The effect of the type II band alignment in the quantum dot (QD) IB SCs on the above percentage is analyzed and the potential of the Ge/Si system for fabrication of the type II QD IB SC is discussed. Also, it is shown that the increase of the sunlight concentration leads to the rise of the potential barrier around QDs and the concentration of S-x approximate to 700 can induce the epsilon(L) = 0.2 eV height barrier in the Ge/Si system, making this a significant result. Furthermore, the increase of the sunlight concentration leads to the separation of the quasi-Fermi levels from the confined states and also leads to the decrease of the recombination activity in QDs. The two-photon absorption in QDs increases rapidly and dominates over recombination at the moderate concentration. As the contributions of QDs to both the photo- and dark currents in the type II QD IB SC are evaluated it is shown that, compared to the conventional Si SCs, the type II Ge QD IB Si SCs can generate about 25% higher photocurrent and conversion efficiency.
Strong barrier effect on the conversion efficiency of solar cells with buried type-II quantum dots
(2007-06-01)
Kechiantz, A. M.
;
Sun, K. W.
;
Kechiyants, H. M.
;
Kocharyan, L. M.
;
應用化學系
A model of a quantum dot (QD) buried solar cell is described. The cell takes advantage of the generation of an additional photocurrent by a two-photon excitation of electrons from the valence band into the conduction band via the confined ( intermediate) state. Since the intermediate states are active recombination centres suppressing the open-circuit voltage and the conversion efficiency either by increasing the dark-current or by arresting the quasi-Fermi level of mobile carriers, a barrier layer promoting the separation of the quasi-Fermi levels is built in around the QDs. Conditions for the separation of the quasi-Fermi levels and the activation of the two-photon generation of mobile carriers were found. Under these conditions the photocurrent and the conversion efficiency of the Ge QD buried Si solar cell exposed to concentrated sunlight must be approximately 25% larger than that of conventional Si solar cells.