Issue 23, 2012
From the journal:

Physical Chemistry Chemical Physics

Vertical phase separation of conjugated polymer and fullerene bulk heterojunction films induced by high pressure carbon dioxide treatment at ambient temperature†

Ryo Kokubuab  and  Yang Yang*ac  

* Corresponding authors

a Department of Materials Science and Engineering, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, California, USA
E-mail: yangy@ucla.edu
Fax: +1-310-206-7353
Tel: +1-310-825-4052

b Furukawa Electric, Co., Ltd., 2-2-3 Marunouchi, Chiyoda-Ku, Tokyo 100-8322, Japan

c California NanoSystems Institute, University of California, Los Angeles, 570 Westwood Plaza, Los Angeles, California, USA

Abstract

The morphology of bulk-heterojunctions (BHJ) is critically important for conjugated polymer and fullerene blend solar cells. To alter the morphology, high pressure (gas phase) carbon dioxide (CO2) treatment is applied to poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) blend films under ambient temperature. This process can achieve vertically phase separated morphology such that PCBM distributes toward the film surface, which is suggested by secondary ion mass spectroscopy (SIMS), contact angle, X-ray photoelectron spectroscopy (XPS) and cross-sectional scanning electron microscope (SEM) studies. While pristine P3HT films do not show a significant change upon CO2 treatment, pristine PCBM films are plasticized in high pressure CO2. Thus, PCBM is selectively plasticized by CO2 in the blend film and is drawn towards the surface due to depressed surface energy, although P3HT tends to distribute around the surface without CO2. This stratification process can enhance solar cell performance. 55% improvement is achieved in the power conversion efficiency of the CO2 treated device compared to the untreated one, indicating that CO2 treatment can be a good candidate for optimizing the morphology and enhancing the performance of BHJ polymer solar cells.

Graphical abstract: Vertical phase separation of conjugated polymer and fullerene bulk heterojunction films induced by high pressure carbon dioxide treatment at ambient temperature

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Article information

DOI
https://doi.org/10.1039/C2CP41161J
Article type
Paper
Submitted
11 Apr 2012
Accepted
12 Apr 2012
First published
15 May 2012

Phys. Chem. Chem. Phys., 2012,14, 8313-8318

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Vertical phase separation of conjugated polymer and fullerene bulk heterojunction films induced by high pressure carbon dioxide treatment at ambient temperature

R. Kokubu and Y. Yang, Phys. Chem. Chem. Phys., 2012, 14, 8313 DOI: 10.1039/C2CP41161J

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