Direct Laser Writing of Complementary Logic Gates and Lateral p–n Diodes in a Solution‐Processible Monolithic Organic Semiconductor

Abstract

Fabrication of p-n structures is a key issue in a number of electronic devices, including rectifying diodes, solar cells, and bipolar transistors. Complementary metal oxide semiconductor (CMOS) technology based on the integration of discrete p-and n-channel field-effect transistors (FETs) on a same substrate has been widely used in a variety of electronic applications and enables the fabrication of integrated circuits with low-power dissipation and high operational stability. In the growing field of organic electronics, efficient large-scale organic CMOS integrated circuits [1,2] as well as lateral p-n diodes [3] have already been realized by thermally evaporating p-and n-type semiconducting organic molecules separately through shadow masks. Alternatively, fabrication of organic inverters by inkjet printing, self-assembly, or spin-coating has also been reported and has demonstrated the enormous potential of solution processing for low-cost, large-area, flexible electronics. [4][5][6][7][8][9][10] However, in spite of remarkable recent advances in high-mobility organic FET materials [11][12][13][14] and nanostructuration techniques, [15] there has still been no reliable approach for effectively patterning p-n bipolar and CMOS microstructures made from solutionprocessible organic semiconductors. We have addressed this issue by exploiting the unique charge-transport properties of the solution-processible dicyanomethylene-substituted quinoidal quaterthiophene [QQT(CN)4], which can be converted from an ambipolar p-type-dominant to n-type semiconductor by either thermal annealing or direct laser writing.The chemical structure of the QQT(CN)4 oligomer is shown in the inset of Figure 1a. Quinoidal oligothiophene derivatives generally show a low highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy bandgap and are very promising candidates for n-type or single-component ambipolar organic FETs. [16][17][18][19][20][21] We have fabricated top-contact bottom-gate organic FETs under ambient conditions by spin-coating a QQT(CN)4 thin film on top of a polyimide gate-dielectric layer and using chromium drain/source electrodes. The transfer and output characteristics displayed in Figure 1 show that the device based on as-prepared QQT(CN)4 thin film exhibits an ambipolar behavior with a predominant hole-transport character. The charge-carrier field-effect mobilities were extracted from the transfer characteristics in the saturated regions. Hole and electron mobilities were measured to be 2 AE 1 Â 10 À3 and 4 AE 1 Â 10 À4 cm 2 V À1 s À1 , respectively. Compared to the QQT(CN)4-based device performance obtained using octadecyltrichlorosilane-treated SiO 2 as gate-dielectric layer and gold top-contact electrodes, [16] these mobility values are substantially lower. However, the use of a polyimide gate dielectric presents the significant advantage of strongly reducing COMMUNICATION www.advmat.de www.MaterialsViews.com

Reversible Conversion of the Majority Carrier Type in Solution‐Processed Ambipolar Quinoidal Oligothiophene Thin Films

“…Both hole and electron fi eld-effect mobilities are extracted from the transfer characteristics in the saturation regime. [ 23 ] We fi nd a hole mobility of 0.07 cm 2 /Vs in both devices and a small increase of the electron mobility from 0.004 to 0.007 cm 2 /Vs. In addition, the solvent treatment causes a little shift of about − 5V in the threshold voltage V th for both hole and electron currents.…”

“…[ 15 ] The dynamics of this thermal effect being very fast in the case of QQT(CN)4 (a few seconds at 180 ° C), similar majority carrier type conversion was obtained by optically pumping the samples in their absorption band to induce some local heating effects, allowing the patterning of CMOS integrated circuits and lateral p-n junctions by direct laser writing. [ 23 ] In addition of being excellent candidates for organic electronic devices, it is worth noting that QQT(CN)4 and quinoidal oligothiophene derivatives are also promising materials for magnetic applications. [ 24 , 25 ] In this communication, we demonstrate that the majority carrier type in QQT(CN)4 thin fi lms can be controlled by the choice of the solvent used for the spin-coating deposition.…”

Majority carrier type conversion in solution-processed organic transistors and flexible complementary logic circuits

“…The AFM height images in inset show the changes of surface morphology in QQT͑CN͒4 crystalline grains caused by annealing, confirming that thermal treatment leads to strong modifications in film morphology. Results published elsewhere 15 have shown that the thermally induced changes in QQT͑CN͒4 film morphology also cause significant variations in the highest occupied molecular orbital ͑from 4.5 to 5.6 eV͒ and lowest unoccupied molecular orbital levels ͑from 3.6 to 4.5 eV͒. All these observations suggest that the strong interplay between molecular orbital energies and molecular packing plays a crucial role on the charge transport properties of QQT͑CN͒4 thin films.…”

Molecular and Supramolecular Architectures of Organic Semiconductors for Field‐Effect Transistor Devices and Sensors: A Synthetic Chemical Perspective

“…[93,94] Quinoidal character is conferred to these oligomers by the dicyanomethylene end-capping at both ends of the oligothiophene backbone that are introduced through the palladium-catalyzed Takahashi reaction [95] followed by oxidation. The first consequence of dicyanovinylene end-capping is a significant decrease in the band gap with respect to the corresponding α-oligothiophenes, which leads to the appearance of a biradicaloid character in the highest homologues of the series, as a consequence of the easy promotion of one electron from the HOMO to the LUMO energy level.…”