Effect of different Na supply methods on thin Cu(In,Ga)Se^sub 2^ solar cells with Al^sub 2^O^sub 3^ rear passivation layers

Effect of different Na supply methods on thin Cu(In,Ga)Se^sub 2^ solar cells with Al^sub 2^O^sub 3^ rear passivation layers

In this work, rear-contact passivated Cu(In,Ga)Se2 (CIGS) solar cells were fabricated without any intentional contact openings between the CIGS and Mo layers. The investigated samples were either Na free or one of two Na supply methods was used, i) a NaF precursor on top of the Al2O3 rear passivatio...

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Bibliographic Details
Published in:Solar energy materials and solar cells Vol. 187; p. 160
Main Authors: Ledinek, Dorothea, Donzel-Gargand, Olivier, Sköld, Markus, Keller, Jan, Edof, Marika
Format: Journal Article
Language:English
Published: Amsterdam Elsevier BV 01-12-2018
Subjects:
Alkalies
Aluminum oxide
Copper
Copper indium gallium selenides
Dependence
Deposition
Electric contacts
Electrical properties
Evaporation
Open circuit voltage
Passivity
Photovoltaic cells
Precursors
Sodium fluoride
Solar cells
Thickness
Thin films
Transmission electron microscopy
Tunnels
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Summary:In this work, rear-contact passivated Cu(In,Ga)Se2 (CIGS) solar cells were fabricated without any intentional contact openings between the CIGS and Mo layers. The investigated samples were either Na free or one of two Na supply methods was used, i) a NaF precursor on top of the Al2O3 rear passivation layer or ii) an in situ post-deposition treatment with NaF after co-evaporation of the CIGS layer. The thickness of the ALD-Al2O3 passivation layer was also varied in order to find an optimal combination of Na supply and passivation layer thickness. Our results from electrical characterization show remarkably different solar cell behavior for different Na supplies. For up to 1 nm thick Al2O3 layers an electronically good contact could be confirmed independently of Na deposition method and content. When the Al2O3 thickness exceeded 1 nm, the current was blocked on all samples except on the samples with the NaF precursor. On these samples the current was not blocked up to an Al2O3 layer thickness of about 6 nm, the maximum thickness we could achieve without the CIGS peeling off the Al2O3 layer. Transmission electron microscopy reveals a porous passivation layer for the samples with a NaF precursor. An analysis of the dependence of the open circuit voltage on temperature (JVT) indicates that a thicker NaF precursor layer lowers the height of the hole barrier at the rear contact for the passivated cells. This energy barrier is also lower for the passivated sample, compared to an unpassivated sample, when both samples have been post-deposition treated.
ISSN:0927-0248