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

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalNot applicablepeer-review

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Author(s)

  • Harrison Ka Hin Lee
  • Zhao Li
  • Iordania Constantinou
  • Franky So
  • Shu Kong So

Detail(s)

Original languageEnglish
Journal / PublicationAdvanced Energy Materials
Volume4
Issue number16
Early online date14 Jul 2014
Publication statusPublished - 18 Nov 2014

Abstract

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.

Research Area(s)

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

Citation Format(s)

Batch-to-batch variation of polymeric photovoltaic materials : Its origin and impacts on charge carrier transport and device performances. / Lee, Harrison Ka Hin; Li, Zhao; Constantinou, Iordania; So, Franky; Tsang, Sai Wing; So, Shu Kong.

In: Advanced Energy Materials, Vol. 4, No. 16, 18.11.2014.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalNot applicablepeer-review