Citation
Antolín Fernández, Elisa and Martí Vega, Antonio and García-Linares Fontes, Pablo and Cánovas Díaz, Enrique and Fuertes Marrón, David and Luque López, Antonio and Farmer, C.D. and Stanley, Colin
(2008).
Demonstration and Analysis of the Photocurrent by absorption of two sub-bandgap photons in a quantum dot intermediate band solar cell.
In: "23rd European Photovoltaic Solar Energy Conference", 01/09/2008-05/09/2008, Valencia, España. ISBN 3-936338-24-8.
Abstract
In order to surpass the efficiency limit of single gap solar cells, intermediate band solar cells (IBSC) have to fulfill two requirements: the production of extra photocurrent by absorption of sub-bandgap photons in electronic transitions involving the intermediate band (IB) and the preservation of a high output voltage, not limited by the existence of this band. This work presents experimental evidence of the production of electron-hole pairs by absorption of two sub-bandgap photons in IBSC prototypes fabricated with InAs/GaAs QD material. The experiments were carried out at low temperatures using a specifically designed modulated photocurrent measurement set-up with two light beams. The results are analysed with the help of a simple equivalent circuit model. This analysis is also used to highlight the relevance of the two-photon mechanism demonstrated in the experiment. It is discussed that, although the absorption of sub-bandgap photons in one of the IB transitions and subsequent thermal escape of carriers is a sufficient mechanism to obtain a photocurrent enhancement, the absorption of sub-bandgap photons in both transitions involving the IB is a requisite for the voltage preservation in IBSCs.