Quantitative Evaluation of Molecular Diffusion in Organic Planar Heterojunctions by Time-of-Flight Secondary Ion Mass Spectroscopy

Kyohei Nakano; Takahiro Shibamori; Keisuke Tajima

doi:10.1021/acsomega.7b01524

Quantitative Evaluation of Molecular Diffusion in Organic Planar Heterojunctions by Time-of-Flight Secondary Ion Mass Spectroscopy

ACS Omega. 2018 Feb 5;3(2):1522-1528. doi: 10.1021/acsomega.7b01524. eCollection 2018 Feb 28.

Authors

Kyohei Nakano¹, Takahiro Shibamori², Keisuke Tajima^{1

3}

Affiliations

¹ RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
² TORAY Research Center, Inc., 3-3-7, Sonoyama, Otsu, Shiga 520-8567, Japan.
³ Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.

Abstract

Understanding molecular diffusion across the interfaces in planar heterojunctions is fundamentally important to improving the performance and stability of organic electronic devices. In this study, we quantitatively evaluated the diffusion of [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) across the interface of planar heterojunctions into the polymer layers by time-of-flight secondary ion mass spectroscopy. Careful calibration allowed the concentration of PCBM to be determined in the polymer layer at concentrations as low as 0.01 wt %. We found that approximately 1 wt % PCBM was present in the poly(3-hexylthiophene) layer in the planar heterojunction with no thermal treatments, indicating that a small amount of PCBM diffused into the polymer layer even at room temperature. The diffusion behavior depended strongly on the crystallinity of the PCBM layer and the properties of the polymer layers such as glass transition temperature. Further analysis suggested that the diffusion of PCBM into the polymer layers was also related to the interface free energy between the layers.