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

Harrison Ka Hin Lee, Zhao Li, Iordania Constantinou, Franky So, Sai Wing Tsang*, Shu Kong SO

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

47 Citations (Scopus)

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.

Original languageEnglish
JournalAdvanced Energy Materials
Volume4
Issue number16
DOIs
Publication statusPublished - 1 Nov 2014

Scopus Subject Areas

  • Renewable Energy, Sustainability and the Environment
  • Materials Science(all)

User-Defined Keywords

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

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