The Influence of MoOx Anode Stoicheometry on the Performance of Bulk Heterojunction Polymer Solar Cells

Bulk heterojunction solar cells containing molybdenum oxide hole extracting anode contacts have been fabricated with varying stoicheometry using radio frequency reactive sputtering from a Molybdenum metal target. A blend of the newly synthesised conjugated polymer poly[9‐(heptadecan‐9‐yl)‐9H‐carbazo...

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Bibliographic Details
Published in:Advanced energy materials 2013-07, Vol.3 (7), p.903-908
Main Authors: Griffin, Jonathan, Watters, Darren C., Yi, Hunan, Iraqi, Ahmed, Lidzey, David, Buckley, Alastair R.
Format: Article
Language:English
Subjects:
Molybdenum
molybdenum oxide
organic photovoltaics
oxidation state
PCDTBT
photoelectron spectroscopy
Photovoltaic cells
Polymers
Solar energy
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Summary:Bulk heterojunction solar cells containing molybdenum oxide hole extracting anode contacts have been fabricated with varying stoicheometry using radio frequency reactive sputtering from a Molybdenum metal target. A blend of the newly synthesised conjugated polymer poly[9‐(heptadecan‐9‐yl)‐9H‐carbazole‐2,7‐diyl‐alt‐(5,6‐bis(octyloxy)‐4,7‐di(thiophen‐2‐yl)benzo[c][1,2,5]thiadiazole)‐5,5‐diyl] (PCDTBT‐8) and fullerene [6,6]‐Phenyl‐C71‐butyric acid methyl ester (PC70BM) was used as the photoactive layer and device results show that anodes with greater than 98% Molybdenum (VI) oxide result in peak power conversion efficiencies of 3.7%.The presence of up to 28% of Mo (V) results in no significant reduction in efficiency, however the presence of metallic Mo (IV) and lower oxidation states lead to severe reductions in device performance due to a combination of a large hole extraction energy barrier of approximately 0.9eV and reduced device stability. Molybdenum oxide oxidation states and their effect on the performance of bulk heterojunction polymer solar cells: ultraviolet photoelectron spectroscopy (UPS) and X‐ray photoelectron spectroscopy (XPS) have shown that the presence of molybdenum oxide states below Mo5+ has severely detrimental effects on the performance of organic photovoltaics (OPV's) due to the occupation of the Mo4d orbital and pinning of the work function at a shallower energy.
ISSN:1614-6832
1614-6840
DOI:10.1002/aenm.201200886