Direct characterization of vertical molecular distributions of organic bulk heterojunction structure by photoemission spectroscopy combined with argon gas cluster ion beam sputtering

• Published in: Applied surface science Vol. 515; p. 146102
• Main Authors: Yun, Dong-Jin, Kim, Seong Heon, Chung, JaeGwan, Kim, Yong-Soo, Shin, Weon-Ho, Ihn, Soo-Ghang, Yun, Sungyoung, Chung, Yeonji, Lee, Seunghyup, Kim, Min, Park, Jong Hwan
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.06.2020
• Subjects: Ar gas cluster ion beam sputtering; Bulk-heterojunction; Organic photovoltaics; Vertical molecular distribution; X-ray photoelectron spectroscopy; Organic photovoltaics; Vertical molecular distribution; Bulk-heterojunction; Ar gas cluster ion beam sputtering; X-ray photoelectron spectroscopy
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2020.146102

The development of a novel, direct, and high-precision XPS depth profiling combined with Ar gas cluster ion beam (GCIB) sputtering method for the characterization of the vertical molecular distribution of an organic BHJ structure. [Display omitted] •The molecular distribution of an organic BHJ was characterized by Ar GCIB-assisted XPS.•The Ar GCIB sputtering can preserve chemical states and electronic structures of P3HT.•The diffusion of PC71BM induces the vertical composition gradient of solvent-annealed BHJ. The characterization of the vertical molecular distribution of organic bulk heterojunction (BHJ) structures is crucial to the development of high-performance organic photovoltaic (OPV) devices. Herein, we report a novel and direct method for the characterization of the vertical composition gradient of a BHJ structure. Ar gas cluster ion beam (GCIB) sputtering provided a uniform sputtering yield that preserved the chemical structure of the organic semiconducting materials. The combination of X-ray photoelectron spectroscopy (XPS) and Ar GCIB sputtering facilitated the accurate analysis of the vertical molecular distribution of a regioregular poly(3-​hexylthiophene) (P3HT) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) BHJ structure. The J-V characteristics and depth profiles of the as-deposited, ethanol-annealed, and chloroform-annealed devices were examined to demonstrate the usefulness of Ar GCIB sputtering in optimizing the BHJ morphology. Chloroform-annealed device exhibited both the best performance and the most homogeneous morphology among the three prepared samples, and the thickness of the P3HT-rich region was substantially reduced from 20 to 10 nm. Consequently, these results provide important information about the correlation between the vertical molecular distribution of a BHJ blend structure and power conversion efficiency of an OPV device.