Document Type

Journal Article

Department/Unit

Department of Physics

Title

Batch-to-batch variation of polymeric photovoltaic materials: Its origin and impacts on charge carrier transport and device performances

Language

English

Abstract

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.A detailed investigation of the impact of molecular weight distribution of a photoactive polymer, poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), on photovoltaic device performance and carrier transport properties is reported. It is found that different batches of as-received polymers have substantial differences in their molecular weight distribution. As revealed by gel permeation chromatography (GPC), two peaks can generally be observed. One of the peaks corresponds to a high molecular weight component and the other peak corresponds to a low molecular weight component. Photovoltaic devices fabricated with a higher proportion of low molecular weight component have power conversion efficiencies (PCEs) reduced from 5.7% to 2.5%. The corresponding charge carrier mobility at the short-circuit region is also significantly reduced from 2.7 × 10-5 to 1.6 × 10-8 cm2 V-1 s-1. The carrier transport properties of the polymers at various temperatures are further analyzed by the Gaussian disorder model (GDM). All polymers have similar energetic disorders. However, they appear to have significant differences in carrier hopping distances. This result provides insight into the origin of the molecular weight effect on carrier transport in polymeric semiconducting materials. Batch-to-batch variation of the photovoltaic performance of devices based on commercial samples of the polymer poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5- (4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) is reported, with efficiency ranging from 5.7% to 2.5%. As revealed by gel permeation chromatography, bimodal distributions are observed in the molecular weight. Charge transport data suggest that low molecular weight components increase the average hopping distance, resulting in lower mobility and poorer photovoltaic performance.

Keywords

charge transport, hopping distance, mobility, molecular weight, photovoltaic devices, polymeric materials

Publication Date

2014

Source Publication Title

Advanced Energy Materials

Volume

4

Issue

16

Start Page

14007681

Publisher

Wiley-VCH Verlag

DOI

10.1002/aenm.201400768

Link to Publisher's Edition

http://dx.doi.org/10.1002/aenm.201400768

ISSN (print)

16146832

ISSN (electronic)

16146840

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