Two-photon spectroscopy for high-efficiency quantum ratchet solar cells
File(s)
Author(s)
Hughes, Kenneth
Type
Thesis
Abstract
In this thesis, experimental work on two quantum-ratchet intermediate band solar cell (QR-IBSC) devices is presented, the results of which represent significant progress in the development high-efficiency solar photovoltaics (PV). An original quantitative analysis of the need for such high-efficiency PV is also presented.
The QR-IBSC implements an irreversible separation of electrons and holes to reduce non-radiative recombination [1]. In this work, this is achieved by spatial separation of electrons and holes using a nanostructure of doped GaAs layers to form a quantum well superlattice in the i-region of a p-i-n junction. The QR-IBSC was first experimentally demonstrated to work by Vaquero-Stainer et al in 2018 [2]. The work presented in this thesis is a direct continuation of the experimental work done by Vaquero-Stainer et al [2].
The first new sample – the Strong Field device – was found to successfully increase the resistance of the two-photon photocurrent against saturation at high interband pulse energies by a factor of ∼10 (∼4 nJ vs. ∼0.3 nJ [2]). The second new sample – the High Barrier device – significantly increased intermediate-state
lifetimes by a factor of ∼1 × 10^7 over those in [2] at low temperatures, leading to observation of a two-photon photocurrent at room temperature. This is the first evidence of such long intermediate lifetimes, and of sequential absorption of two sub-bandgap photons in an IBSC at room temperature using a double-demodulation technique.
These results, in particular the long lifetime and high-temperature operation of the sequential absorption mechanism, represent significant progress on the path towards real-world operation of the QR-IBSC.
The QR-IBSC implements an irreversible separation of electrons and holes to reduce non-radiative recombination [1]. In this work, this is achieved by spatial separation of electrons and holes using a nanostructure of doped GaAs layers to form a quantum well superlattice in the i-region of a p-i-n junction. The QR-IBSC was first experimentally demonstrated to work by Vaquero-Stainer et al in 2018 [2]. The work presented in this thesis is a direct continuation of the experimental work done by Vaquero-Stainer et al [2].
The first new sample – the Strong Field device – was found to successfully increase the resistance of the two-photon photocurrent against saturation at high interband pulse energies by a factor of ∼10 (∼4 nJ vs. ∼0.3 nJ [2]). The second new sample – the High Barrier device – significantly increased intermediate-state
lifetimes by a factor of ∼1 × 10^7 over those in [2] at low temperatures, leading to observation of a two-photon photocurrent at room temperature. This is the first evidence of such long intermediate lifetimes, and of sequential absorption of two sub-bandgap photons in an IBSC at room temperature using a double-demodulation technique.
These results, in particular the long lifetime and high-temperature operation of the sequential absorption mechanism, represent significant progress on the path towards real-world operation of the QR-IBSC.
Version
Open Access
Date Issued
2021-12
Date Awarded
2022-09
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Phillips, Christopher
Sponsor
Engineering and Physical Sciences Research Council
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)