Solution‐Processed Small‐Molecule Bulk Heterojunction Ambipolar Transistors

Abstract

Organic thin-fi lm transistors (OTFTs) have attracted much attention due to their potential applications in high-value, low-cost electronic devices, including displays, sensors, radio-frequency identifi cation components, and e-papers. [1][2][3] Current research in OTFT materials is focused primarily on the design and synthesis of conjugated organic compounds and polymers that are environmentally stable and capable of carrier transport. Several conjugated organic compounds and polymers have been developed with promising carrier mobilities, comparable to that of amorphous silicon. [4][5][6] To exploit such materials in a wider range of practical applications, high-performance inverters, which are the building blocks of integrated circuits (ICs), must be developed. Complementary metal-oxide semiconductor (CMOS) technology is desirable for the preparation of ICs because it provides straightforward circuit design, good noise margins, low power consumption, and robust operation. Organic CMOS technology requires the use of p-and n-type transistors on the same substrate; however, the separate vacuum-deposition of p-and n-type semiconductors increases the complexity of the circuit fabrication process. [ 7,8 ] To overcome this problem, researchers have explored several strategies, including: i) ambipolar OTFTs featuring symmetric or asymmetric source and drain electrodes for single organic semiconductors; [9][10][11][12] ii) bilayer structures consisting of hole-and electron-transporting organic compounds; [13][14][15][16] and iii) blending two organic semiconductors with different polarities to eliminate the need to pattern the p-and n-channel semiconductors in separation regions. [17][18][19][20] In a single-material confi guration, the effi cient injection of both holes and electrons is the key factor affecting the performance of ambipolar OTFTs. Improved carrier mobility can be achieved by lowering the barrier between the energy levels of the metal and those of the highest occupied molecular orbital (HOMO) of the organic semiconductor for hole transport, and of the lowest unoccupied molecular orbital (LUMO) for electron transport. Most organic semiconductors have a wide band gap (ca. 2-3 eV), resulting in a mismatch between the work function of the electrode and the organic semiconductor for at least one of the carriers. Although devices featuring asymmetric electrodes could circumvent this drawback, the preparation of such a device demands an additional deposition step. Therefore, several research groups have investigated the use of a bilayer structure, with carrier mobility of electrons and holes reaching as Shiau-Shin Cheng , Peng-Yi Huang , Mohan Ramesh , Hsiu-Chieh Chang , Li-Ming Chen , Chia-Ming Yeh , Chun-Lin Fung , Meng-Chyi Wu , Chung-Chi Liu , Choongik Kim ,* Hong-Cheu Lin , Ming-Chou Chen ,* and Chih-Wei Solution-Processed Small-Molecule Bulk Heterojunction Ambipolar Transistors

Recent Advances in Ambipolar Transistors for Functional Applications

“…First, Single‐component organic materials with appropriate energy levels and interface contacts and 2D materials with intrinsic ambipolar charge transport characteristics can be utilized individually for ambipolar behavior and just only one material is responsible for the electron and hole transport and accumulation within semiconducting channel . Second, thin films of semiconducting polymer blends, mixtures and composites fabricated via solution‐processing and vacuum coevaporation can also achieve ambipolar performance and controlling the morphology of blends well is extremely crucial for realizing better ambipolar behavior . Apparently, these two or three materials (p‐ or n‐type) take charge of electron and hole transport separately and efficiently but also in identical and entire blending semiconductors.…”

Fused-Thiophene Based Materials for Organic Photovoltaics and Dye-Sensitized Solar Cells

“…Despite the excellent performance of fused-thiophenes in OTFTs [61][62][63][64][65][66], fused-thiophene-based OPV and DSSC studies are still in their infancy. It is well known that there are a number of factors determining the efficiency of the photovoltaic cells, and that the multiparameter problem remains to be solved.…”

Investigating the Thermal Stability of Organic Thin‐Film Transistors and Phototransistors Based on [1]‐Benzothieno‐[3,2‐b]‐[1]‐benzothiophene Dimeric Derivatives

“…Based on XRD analysis and compared with the molecular lengths of BTBT-Ph-BTBT (28.4 ) and BTBT-DPh-BTBT (32.8 ), the actual inclination angles of the materials BTBT-Ph-BTBT and BTBT-DPh-BTBT were 64 and 658, respectively. [22] The thin-film XRD patterns of BTBT-Ph-BTBT and BTBT-DPh-BTBT displayed stronger reflection intensity with increasing deposition temperature, which indicates better ordering with increasing deposition temperatures. These results are consistent with the field-effect response in the actual devices.…”