Synthesis and properties of multi-triarylamme-substituted carbazole-based dendrimers with an oligothiophene core for potential applications in organic solar cells and light-emitting diodes

Jianping Lu, Ping Fang Xia, Pik Kwan Lo, Ye Tao*, Ricky M S WONG

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

131 Citations (Scopus)

Abstract

In this paper, we report on the synthesis and properties of a novel series of multi-triarylamine-substituted carbazole-based dendrimers G 2-OTP(n)-G2 (n = 2-5) with an oligothiophene core. The length of the oligothiophene core varied from 2 to 5 thiophene units. It was found that both the absorption and fluorescence emission peaks red-shifted with increasing oligothiophene core length. As a result, the power conversion efficiencies of the as-fabricated solar cells using the composite of these dendrimers and PCBM as the photoactive layer increased with increasing oligothiophene core length, from 0.04% for G2-DTP-G2 to 0.13% for G2-PTP-G2 under AM 1.5 simulated solar illumination at an irradiation intensity of 100 mW/cm2. After a thermal annealing at 150°C for 15 min under nitrogen, however, the devices based on the G2-DTP-G2:PCBM blend exhibited the most dramatic improvement and almost best performance, although other devices also showed some improvement. Since only G2-DTP-G2 is the a crystalline material among these four dendrimers, the dramatic improvement of the associated devices after annealing is attributed to the formation of some nanocrystalline structures in the active layer, as indicated by DSC analysis and AFM studies. In addition, we have demonstrated that both G2-DTP- G2 and G2-PTP-G2 can be used as hole-transporting emitters in organic light-emitting diodes (OLEDs) with 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI) as a hole-blocking layer and LiF/Al as the cathode. Because of the low hole injection barrier, the turn-on voltages of the OLED devices were as low as 4 V. G2-DTP-G2 exhibited blue electroluminescence with a maximum luminance of 1660 cd/m 2 at 15.5 V, while G2-PTP-G2 emitted yellow light with a highest luminance of 1000 cd/m2 at 19 V.

Original languageEnglish
Pages (from-to)6194-6203
Number of pages10
JournalChemistry of Materials
Volume18
Issue number26
DOIs
Publication statusPublished - 26 Dec 2006

Scopus Subject Areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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