期刊
ACS APPLIED MATERIALS & INTERFACES
卷 10, 期 8, 页码 7296-7303出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsami.7b19279
关键词
organic semiconductors; friction anisotropy; AFM; OFETs; C8-BTBT
资金
- FPU from the Spanish Ministry
- Severo Ochoa Program for Centers of Excellence in RD [SEV-2015-0496]
- ERC [StG 2012-306826 e-GAMES]
- Spanish Government [MAT2016-77852-C2-1-R, FANCY CTQ2016-80030-R, MAT2013-47869-C4-1-P]
- Networking Research Center on Bioengineering, Biomaterials, and Nanomedicine (CIBER-BBN)
- Generalitat de Catalunya [2017-SGR-668, 2014-SGR-17]
- MINECO [MAT2015-68994-REDC]
Disentangling the details of the vertical distribution of small semiconductor molecules blended with polystyrene (PS) and the contact properties are issues of fundamental value for designing strategies to optimize small-molecule:polymer blend organic transistors. These questions are addressed here for ultrathin blends of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) and PS processed by a solution-shearing technique using three different blend composition ratios. We show that friction force microscopy (FFM) allows the determination of the lateral and vertical distribution of the two materials at the nanoscale. Our results demonstrate a three-layer stratification of the blend: a film of C8-BTBT of few molecular layers with crystalline order sandwiched between a PS-rich layer at the bottom (a few nm thick) acting as a passivating dielectric layer and a PS-rich skin layer on the top (similar to 1 nm) conferring stability to the devices. Kelvin probe force microscopy (KPFM) measurements performed in operating organic field-effect transistors (OFETs) reveal that the devices are strongly contact-limited and suggest contact doping as a route for device optimization. By excluding the effect of the contacts, field-effect mobility values in the channel as high as 10 cm(2) V-1 s(-1) are obtained. Our findings, obtained via a combination of FFM and KPFM, provide a satisfactory explanation of the different electrical performances of the OFETs as a function of the blend composition ratio and by doping the contacts.
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