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Proceedings Paper

Efficient conventional- and inverted-type photovoltaic cells using a planar alternating polythiophene copolymer
Author(s): Wonho Lee; Han Young Woo
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Paper Abstract

Over the past few decades, the interest in photovoltaic cells has increased due to the growing demand for renewable and clean energy sources. Bulk-heterojunction (BHJ) polymer solar cells (PSCs) comprising interpenetrating networks of conjugated polymers (as an electron donor) and fullerene derivatives (as an electron acceptor) have attracted much attention, owing to their many advantages such as chemically tunable optoelectronic properties, light weight, cost-effective low temperature and solution-based processing for flexible large-area devices.[1] Here we report a simple and efficient D-A type photovoltaic polymeric structure based on alternating thiophene-benzothiadiazole units, poly{5,6-bis(octyloxy)-4-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole} (PTBT, Scheme 1). Solubilizing alkoxy groups were introduced to the benzothiadiazole (BT) moiety to maximize the planarity with a minimized torsional angle in the main backbone. A closer inspection of the molecular structure by computational modeling showed that the alkoxy substituents on BT have little effect on the planarity, torsional angle and resulting π-π stacking property of the conjugated backbone when compared to the unsubstitued one. More importantly, this molecular design strategy was proven not to increase the HOMO energy level of the polymer, yielding a high VOC (0.87 V) of the resulting PSC, which is one of the highest values reported so far among thiophene-based polymers. When the PTBT polymer was blended with [6,6]phenyl-C61-butyric acid methyl ester (PC61BM) as an acceptor, highly promising performance was achieved with PCEs of 5.9% and 5.3% for conventional and inverted devices. A main advantage of PTBT is its simple molecular structure via relatively easy synthetic routes without a deterioration of the photovoltaic properties. Easy synthesis and a simple molecular structure are also an important factor to be considered for mass production.

Paper Details

Date Published:
Proc. SPIE 8477, Organic Photovoltaics XIII, 84770B; doi: 10.1117/12.928818
Show Author Affiliations
Wonho Lee, Pusan National Univ. (Korea, Republic of)
Han Young Woo, Pusan National Univ (Korea, Republic of)

Published in SPIE Proceedings Vol. 8477:
Organic Photovoltaics XIII
Zakya H. Kafafi; Christoph J. Brabec; Paul A. Lane, Editor(s)

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