Introduction to Organic Thin Film Transistors and Design of n-Channel Organic Semiconductors

Abstract

The development of new organic semiconductors with improved performance in organic thin film transistors (OTFTs) is a major challenge for materials chemists. There is a particular need to develop air-stable n-channel (electron-conducting) organic semiconductors with performance comparable to that of p-channel (hole-conducting) materials, for organic electronics to realize the benefits of complementary circuit design, i.e., the ability to switch transistors with either positive or negative gate voltages. There have been significant advancements in the past five years. In terms of standard OTFT metrics such as the field effect mobility (µ FET ) and on-to-off current ratio (I ON /I OFF ), n-channel OTFTs have achieved performance comparable both to that of n-channel amorphous silicon TFTs and to that of the best reported p-channel (hole-conducting) OTFTs; however, issues of device stability linger. This review provides a detailed introduction to OTFTs, summarizes recent progress in the development of new n-channel organic semiconductors, and discusses the critical properties that any prospective n-channel material must have. Methods important to semiconductor design such as electronic structure calculations and synthetic structural modifications are highlighted in a case study of the development of a new n-channel material based on a terthiophene modified with electron-withdrawing groups. The review concludes with a discussion of directions for future work in this area.

Optoelectronic and Semiconducting Properties of Conjugated Polymers Composed of Thiazolo[5,4-d]thiazole and Arene Imides Linked by Ethynylene Bridges

“…Thus, the AEAs estimated for the infinite polymer chains II -VI are within the range of 3.0 − 4.0 eV proposed by Newman et al 42 for n-type organic semiconductors, hence the most favorable electron injection can be expected for polymer I. Likewise, IP must be low enough to allow an easy hole injection into the HOCO the semiconductor.…”

“…In organic crystals, the outer reorganization energy is in the order of few tenths of an electronvolt or lower, contrary to charge transfer in solution wherein the external part dominates. 3,[42][43][44][45] Different values for λ s , ranging between 0.01 and 0.2 eV, have been proposed and employed in literature. [46][47][48][49] As in previous works, λ s was fixed at 0.1 eV in order to facilitate the comparison with previous rate constants reported for PAEs.…”

Bis(arylene-ethynylene)-s-tetrazines: A Promising Family of n-Type Organic Semiconductors?

“…Generally speaking, in organic molecular crystals the outer contribution λ s is of the order of one tenth of eV, 36,37 contrarily to charge transfer in solution wherein the external part might dominate, [37][38][39][40][41][42] and is fixed here at 0.1 eV. Conversely, the internal reorganization energy λ i is calculated at the Density Functional Theory (DFT) levels and enters into equation…”

“…EA of a semiconductor should amount at least to 3.0 eV for an easy electron injection. 38,49 However, its stability in ambient conditions could be compromised by high EA values as well as other factors as the crystal packing and film morphology. 38,[50][51][52] The adiabatic (AEA) and vertical (VEA) electron affinity were calculated as follows…”

Optical Properties of ZnO/ZnS and ZnO/ZnTe Heterostructures for Photovoltaic Applications

“…poly(3-hexylthiophene) (P3HT), which are typically more conductive and air stable than typical n-channel polymers. 59 …”