Browsing by Author "Savvidis, Pavlos G."

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Highly Efficient Flexible Hybrid Nanocrystal-Cu(In,Ga)Se-2 (CIGS) Solar Cells
(2015-01-21)
Liao, Yu-Kuang
;
Brossard, Mael
;
Hsieh, Dan-Hua
;
Lin, Tzu-Neng
;
Charlton, Martin D. B.
A novel scheme for hybridizing inkjet-printed thin film Cu(In,Ga)Se-2 (CIGS) solar cells with self-assembled clusters of nanocrystal quantum dots (NQDs), which provides a 10.9% relative enhancement of the photon conversion efficiency (PCE), is demonstrated. A non-uniform layer of NQD aggregates is deposited between the transparent conductive oxide and a CdS/CIGS p-n junction using low cost pulsed-spray deposition. Hybridization significantly improves the external quantum efficiency of the hybrid devices in the absorption range of the NQDs and in the red to near-IR parts of the spectrum. The low wavelength response enhancement is found to be induced by luminescent down-shifting (LDS) from the NQD layer, while the increase at longer wavelengths is attributed to internal scattering from NQD aggregates. LDS is demonstrated using time-resolved spectroscopy, and the morphology of the NQD layer is investigated in fluorescence microscopy and cross-sectional transmission electron microscopy. The influence of the NQD dose on the PCE of the hybrid devices is investigated and an optimum value is obtained. The low costs and limited material consumptions associated with pulsed-spray deposition make these flexible hybrid devices promising candidates to help push thin-film photovoltaic technology towards grid parity.
Novel Non-radiative Exciton Harvesting Scheme Yields a 15% Efficiency Improvement in High-Efficiency III-V Solar Cells
(2015-02-01)
Brossard, Mael
;
Hong, Chung-Yu
;
Hung, Mumin
;
Yu, Peichen
;
Charlton, Martin D. B.
High-effi ciency III-V solar cells typically incorporate an indirect wide-bandgap semiconductor as a passivation layer to limit surface recombination at higher photon energies. The poor extraction effi ciency of the carriers photogenerated in this window layer limits the performance of the devices in the high-energy region of the spectrum. To address this problem, a resonance energy transfer (RET)-mediated luminescent down-shifting (LDS) layer is engineered by depositing an epilayer of colloidal quantum dots (QDs) on an InGaP solar cell. In this confi guration, while the QDs act as a standard LDS layer, excitons are also funneled from the window layer to the QD epilayer using near-fi eld RET. The luminescence energy of the QDs is tuned below the bandgap of the window layer and the emitted light is absorbed in the p-n junction, where carriers are generated and effi ciently extracted. The overall performance of the solar cell is found to be signifi cantly improved after hybridization, with a large 14.6% relative and 2% absolute enhancement of the photon conversion effi ciency.