Temperature-dependent characteristics of organic transistors are analysed thoroughly using interface approximation. In contrast to amorphous silicon transistors, it is characteristic of organic transistors that the accumulation layer is concentrated on the first monolayer, and it is appropriate to consider interface charge rather than band bending. On the basis of this model, observed characteristics of hexamethylenetetrathiafulvalene (HMTTF) and dibenzotetrathiafulvalene (DBTTF) transistors with various surface treatments are analysed, and the trap distribution is extracted. In turn, starting from a simple exponential distribution, we can reproduce the temperature-dependent transistor characteristics as well as the gate voltage dependence of the activation energy, so we can investigate various aspects of organic transistors self-consistently under the interface approximation. Small deviation from such an ideal transistor operation is discussed assuming the presence of an energetically discrete trap level, which leads to a hump in the transfer characteristics. The contact resistance is estimated by measuring the transfer characteristics up to the linear region.

We have investigated trap density of states (trap DOS) in n-channel organic field-effect transistors based on N,N ’-bis(cyclohexyl)naphthalene diimide (Cy-NDI) and dimethyldicyanoquinonediimine (DMDCNQI). A new method is proposed to extract trap DOS from the Arrhenius plot of the temperature-dependent transconductance. Double exponential trap DOS are observed, in which Cy-NDI has considerable deep states, by contrast, DMDCNQI has substantial tail states. In addition, numerical simulation of the transistor characteristics has been conducted by assuming an exponential trap distribution and the interface approximation. Temperature dependence of transfer characteristics are well reproduced only using several parameters, and the trap DOS obtained from the simulated characteristics are in good agreement with the assumed trap DOS, indicating that our analysis is self-consistent. Although the experimentally obtained Meyer-Neldel temperature is related to the trap distribution width, the simulation satisfies the Meyer-Neldel rule only very phenomenologically. The simulation also reveals that the subthreshold swing is not always a good indicator of the total trap amount, because it also largely depends on the trap distribution width. Finally, band transport is explored from the simulation having a small number of traps. A crossing point of the transfer curves and negative activation energy above a certain gate voltage are observed in the simulated characteristics, where the critical VG above which band transport is realized is determined by the sum of the trapped and free charge states below the conduction band edge

Basic small-molecule organic electron acceptors and donors such as dicyanoquinonediimine (DCNQI), tetracyanoquinodimethane (TCNQ), and tetramethyltetrathiafulvalene (TMTTF) do not smoothly form thin films by vacuum evaporation owing to the high vapor pressures. The thin films are, however, fabricated by low-vacuum evaporation, and the resulting organic thin-film transistors have exhibited remarkably improved performance.

Reliable electrochemical investigations of electrode materials are indispensable for the development of next-generation energy storage devices. In the case of multivalent cation-based electrochemistry, intense attention should be paid to the cell configuration for obtaining reliable data. In particular, the electrolyte and reference electrode must be appropriately selected considering the potential window of electrolyte and the validity of reference. Here, we demonstrate the detailed electrochemical examination for the Mg2+-storage capability of the NASICON-type framework derived from Na3V2(PO4)3 (NVP). A combination of the Mg­(BF4)2-based electrolyte with high anodic stability and the reliable Ag pseudo-reference electrode offers decent electrochemical test results. Despite suffering from the polarization concerning magnesiation, the desodiated NVP electrode can deliver a well-defined discharge plateau at ∼2.7 V (vs Mg2+/Mg) with the reversible capacity of >100 mAh g–1 at room temperature. The impedance analysis results indicate that the increased charge transfer resistance on discharging due to the high energy barrier for desolvation of divalent cations is responsible for the large polarization but not extremely significant, allowing for the room-temperature operation. The findings obtained herein also highlight the importance of the structural robustness of host lattice, which is required to withstand the strong amorphization during Na+ extraction and Mg2+ insertion/extraction.

Tetrathiafulvalene (TTF), pentacene, and quarterthiophene with tert-butyl substituents are synthesized, and the crystal structures and the transistor properties are investigated. The tetracyanoquinodimethane (TCNQ) complex of tert-butyl TTF constructs highly one-dimensional segregated columns with tetragonal crystal symmetry.