Double Beneficial Role of Fluorinated Fullerene Dopants on Organic Thin-Film Transistors: Structural Stability and Improved Performance

Abstract

The present work assesses improved carrier injection in organic field-effect transistors by contact doping and provides fundamental insight into the multiple impacts that the dopant/semiconductor interface details have on the long-term and thermal stability of devices. We investigate donor [1]benzothieno-[3,2-b]-[1]benzothiophene (BTBT) derivatives with one and two octyl side chains attached to the core, therefore constituting asymmetric (BTBT-C8) and symmetric (C8-BTBT-C8) molecules, respectively. Our results reveal that films formed out of the asymmetric BTBT-C8 expose the same alkyl-terminated surface as the C8-BTBT-C8 films do. In both cases, the consequence of depositing fluorinated fullerene (C 60 F 48 ) as a molecular p-dopant is the formation of C 60 F 48 crystalline islands decorating the step edges of the underlying semiconductor film surface. We demonstrate that local work function changes along with a peculiar nanomorphology lead to the double beneficial effect of lowering the contact resistance and providing long-term and enhanced thermal stability of the devices.

Enhancing Long‐Term Device Stability Using Thin Film Blends of Small Molecule Semiconductors and Insulating Polymers to Trap Surface‐Induced Polymorphs

“…Thin films of C 8 O-BTBT-OC 8 are less smooth than the blended films with smaller crystal domains, and after 3 months the films suffer a significant dewetting effect, as previously reported for similar derivatives (Figure 3). [33][34][35] After 1.5 years a recrystallization process takes place and clearly defined crystals are observed on the surface which belong to the Bulk phase, as previously observed in spin-coated films of C 8 O-BTBT-OC 8 ( Figures S11 and S12, Supporting Information). [21] In the case of the thin films based on the lower molecular weight PS3K some morphological changes were observed after 3 months, although the films continued to be uniform and continuous (Figure 3).…”

Structures, Properties, and Device Applications for [1]Benzothieno[3,2‐b]Benzothiophene Derivatives

“…[139,140] Basically, dopant could improve thin-film morphology, crystal quality, molecular parking order, and carrier transport. [141][142][143] There are several basic requirements for selecting dopants, including similar solubility, molecular configuration and size with OSC, and appropriate energy levels for charge transfer. [144] Anthopoulos et al improved device performance by doping, in which three different additives fluorinated fullerene C 60 F 48 , Lewis acids B(C 6 F 5 ) 3 , and Zn(C 6 F 5 ) 2 were added, respectively, to obtain specific C8-BTBT ternary blend systems with better crystallization.…”

Effect of the Organic Semiconductor Side Groups on the Structural and Electronic Properties of Their Interface with Dopants

“…46−48 Nevertheless, for the thicknesses typically employed in OFETs (>20 nm), C8-BTBT forms a closed film. 42 Out-of-plane XRD shows (00l) Bragg peaks up to multiple orders, proving that the films are oriented with the (001) crystal face parallel to the surface for both molecules (see Figure S2a for DPh-BTBT and ref 42 for C8-BTBT). The interplanar spacing (d 001 ) obtained from the Bragg peaks is 2.01 nm for DPh-BTBT and 2.91 nm for C8-BTBT, in full agreement with the reported crystalline structure 35,37 and the AFM topographical data (Figure 1e,f).…”

“…The (111) reflection can be seen in the out-of-plane XRD data reported in our previous work. 42 Indeed, the in-plane scans of bare DPh-BTBT/nSiO 2 (black spectrum in Figure 2b Figure 2b). These data clearly show that the position and width of the peaks of the BTBT films remain unaltered, that is, C 60 F 48 deposition does not disrupt the structure and packing of the underlying films.…”

“…The growth mode of C 60 F 48 on C8-BTBT and the associated beneficial effect on the stability of the OSC film have been recently reported by our group. 42 The C 60 F 48 crystallites on C8-BTBT present a distribution of heights, varying in multiples of 1 nm, which equals the lattice spacing d 111 of the oriented FCC structure. For the deposited C 60 F 48 coverages of 1 and 3 nm, the heights range 3−5 nm and up to 9−12 nm, respectively.…”