1 GHz Pentacene Diode Rectifiers Enabled by Controlled Film Deposition on SAM‐Treated Au Anodes

Abstract

the diode was consisted of printed inorganic layers of Si and NbSi 2 microparticles with an organic binder. [ 8 ] Because the operational frequency of the diode scales with its charge-transporting properties, the realization of the UHF rectifi er based on organic materials has been a challenge. Recently, a rectifi er with a 3 dB frequency reaching an impressive 700 MHz in terms of voltage was demonstrated, but its voltage output ( V out ) at 1 GHz was only 0.31 V for an AC input signal with 2 V amplitude. [ 9 ] In order to achieve ultrahigh frequency performance organic rectifi ers, which commonly consist of diodes and capacitors, it is important to achieve high charge carrier injection effi ciency and mobility within the organic semiconductor layer. Even if the work function of a metal electrode is selected to match the highest occupied molecular orbital (HOMO) level of an organic semiconductor, the formation of an adversely aligned dipole or other (e.g., oxide) interface layer can lead to a hole injection barrier, limiting charge injection. [ 10,11 ] Self-assembled monolayers (SAMs) represent one good candidate for ensuring effi cient charge injection by specifi cally tuning the metal work function. [12][13][14][15] Interfacial charge trapping can also sometimes help. [ 16 ] The permanent dipole moment of suitably selected SAM molecules changes the effective metal work function, reducing the charge injection barrier. SAMs may also be used to enhance the properties of gate dielectric layers in organic thin fi lm transistors (TFTs). [ 17,18 ] In addition to SAM-based metal work function tuning, surface energy characteristics are also altered by the SAM functional groups. This in turn can modify the subsequent deposition of organic semiconductor layers. In particular, pentacene grain formation, one of the important factors determining pentacene thin fi lm mobility, is much affected by substrate surface energy. The SAM molecule functional groups can be selected to lower the surface energy, thereby enhancing molecular packing and improving mobility. [ 19 ] Studies have shown that the orientation of pentacene deposited on Au is different to that deposited on SAM-treated Au. [20][21][22] The effect that such structural differences have on electrical characteristics for transport in the vertical direction (normal to the fi lm plane) has not been investigated to any great extent; the great majority of studies have focused on in-plane transport within TFT structures. [23][24][25] In this study, we investigated vertical diode structures instead of TFTs and as a result of the understanding gained we were able to fabricate ultrafast pentacene rectifi ers with V out = 3.8 V at 1 GHz and with a 3 dB frequency, in terms of voltage, of 1.24 GHz, the highest value reported to date. [ 8 ] Conjugated organic molecules such as pentacene, demonstrate strong electron-vibrational mode coupling with a dependence on orientation. This allows us to use Raman spectroscopy as a probe for molecular orientation. [ 26 ] Here, For automatic det...

A Mechanically Durable and Flexible Organic Rectifying Diode with a Polyethylenimine Ethoxylated Cathode

“…When measured in N 2 , the Au/CuPc/PEIE/Au devices show a slightly lower RR of 1.8 × 10 6 and a current density of 1.8 A cm −2 . [ 7,8,14,[17][18][19][20][21] Compared with previous studies, our Au/ CuPc/PEIE/Au diode shows among the highest RRs and current densities, even though it is driven in ambient conditions. This can be attributed to the propensity of CuPc to be doped by O 2 .…”

“…The forward current through the device can be maximized by utilizing thin active layers with high electron and hole mobilities and a reduced recombination rate along with the use of ohmic contacts with low series resistances. In addition, a recent report showed an Au/2,3,4,5,6pentafl uorobenzenethiol/pentacene/Al [ 8 ] diode which exhibited a current density and RR of 1.0 × 10 2 A cm −2 and 10 7 , respectively. This must all be realized while suppressing the leakage current through the device.…”

“…[6][7][8] In addition, especially in the case of vacuum deposited small molecules, the surface properties of the bottom contact have a signifi cant effect on the electrical properties of the layer. The forward current through the device can be maximized by utilizing thin active layers with high electron and hole mobilities and a reduced recombination rate along with the use of ohmic contacts with low series resistances.…”

Molecular Electronics: From Single‐Molecule to Large‐Area Devices

“…Molecular devices are also prone for high‐frequency operations and the demonstration of a molecular diode at 18 GHz opens the door to operate organic and molecular devices in the high‐frequency regime. This results will allow exploring theoretically predicted new effects, such as, dynamic resonances inducing an amplification of the conductance of the molecular devices, or, in future practical applications the use of organic diodes in energy harvesting systems (at Wi−Fi and other electromagnetic radiation) on flexible substrates. We also note that some unexpected results not reported previously (e. g. the large force load dependency of the tunnel factor and HOMO position, the “two‐peaked” distribution of conductance on nanodot‐molecule junctions) ought to be compared with results from other molecular device platform for a better understanding and towards a global consensus on electron transport through molecular nanostructures.…”

Potentiometric Parameterization of Dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene Field‐Effect Transistors with a Varying Degree of Nonidealities

“…A recent report on organic diodes on PFBT-Au also showed smaller but better-ordered and larger-mobility pentacene grains on SAMs. [40] It is therefore inferred that the classical grain-size dependence of the mobility may be reversed in cases where metal-induced frustration plays an important role. Therefore, the whole analysis up to this point delivers a solid understanding that the performance improvement by the SAMs, first viewed as enhanced I D in Figure 1c, arises in fact from both decreased R c and increased µ ch , with fairly comparable contribution.…”