Correlation between exciton lifetime distribution and morphology of bulk heterojunction films after solvent annealing

Jen Hsien Huang, Kuang Chieh Li, Fan Ching Chien, Yu Sheng Hsiao, Dhananjay Kekuda, Peilin Chen, Hong-Cheu Lin, Kuo Chuan Ho, Chih Wei Chu*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

33 Scopus citations

Abstract

We have synthesized a low-bandgap polymer, bithiazole-based polymer (PCPDTTBT) containing cyclopentadithiophene and thiophene units, and studied its opticophysical properties and morphologies in bulk heterojunction films after annealing. We used confocal optical microscopy in conjunction with a fluorescence module to record exciton lifetime images within photoactive layers of PCPDTTBT and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). These images, which were consistent with those recorded using atomic force microscopy and transmission electron microscopy, revealed that phase separation of PCPDTTBT and PCBM occurred during slow solvent evaporation. This phase separation not only provided bicontinuous pathways for carrier transport to the respective electrodes but also enhanced the degree of polymer chain stacking, thereby improving the absorption and balancing the electron and hole mobilities. We tested the performance of solar cells incorporating PCPDTTBT and various fullerene derivatives. Under AM 1.5 G illumination (100 mW cm-2), a PCPDTTBT/bisPCBM-based solar cell exhibited a power conversion efficiency of 3.8%, with a short circuit current of 7.3 mA cm-2, an open circuit voltage of 0.88 V, and a fill factor of 59.1%.

Original languageEnglish
Pages (from-to)9062-9069
Number of pages8
JournalJournal of Physical Chemistry C
Volume114
Issue number19
DOIs
StatePublished - 20 May 2010

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