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...

Colloidal quantum dots (QDs) stand at the forefront of a variety of photonic applications given their narrow spectral bandwidth and near-unity luminescence e ciency. Integrating desired forms of QD lms into photonic systems without compromising their optical or transport characteristics is the key to bridging the gap between expectations and outcomes. Here, we devise a dual-ligand passivation system comprising photocrosslinkable ligands and dispersing ligands to enable QDs to be universally compatible with solution-based patterning techniques. The successful control on the structure of both ligands allows multiscale, direct patterning of the dual-ligand QDs on various substrates via commercialized photolithography (i-line) or inkjet printing systems without compromising the optical properties of QDs or the optoelectronic performances of the devices implementing them. Our approach offers a versatile way of creating various structures of luminescent QDs in a cost-effective and non-destructive manner, and thus enables the implementation of QDs in a range of photonic applications. MainColloidal quantum dots (QDs) are promising materials for use in next-generation light sources due to their wide-ranging bandgap tunability, narrow spectral bandwidths, and near-unity luminescence quantum yields (QY) [1][2][3][4][5] . Together with the capability of cost-effective solution processing, QDs have become the key light-emissive materials for information displays 3,5−7 . The patterned QD down-conversion layer on blue light-emitting diodes (LEDs) renders high-color reproduction and ultra-high image quality in full-color displays 8,9 . Likewise, a laterally patterned array consisting of red, green, and blue (RGB) QD-LEDs, in which QDs convert electrically pumped charge carriers into photons, allows for excellent color gamut and brightness as well as light-weight, thin, and exible form factors [10][11][12][13] , which are suited for wearable neareye displays for virtual reality (VR) and augmented reality (AR) devices. For these "mixed-reality" applications, the QD deposition process should enable the patterning of RGB QDs (or RG QDs along with the bank) into a few micrometer sub-pixels over a large area with high-precision and high-delity 14,15 . At the same time, the process should not disrupt the optical and transport characteristics of QDs and adjacent functional layers. Moreover, from a practical standpoint, it poses great bene t if one can use equipment that are already deployed in display device manufacturing steps for the patterning process.

We demonstrated modulation of charge carrier densities in all-solution-processed organic field-effect transistors (OFETs) by modifying the injection properties with self-assembled monolayers (SAMs). The all-solution-processed OFETs based on an n-type polymer with inkjet-printed Ag electrodes were fabricated as a test platform, and the injection properties were modified by the SAMs. Two types of SAMs with different dipole direction, thiophenol (TP) and pentafluorobenzene thiol (PFBT) were employed, modifying the work function of the inkjet-printed Ag (4.9 eV) to 4.66 eV and 5.24 eV with TP and PFBT treatments, respectively. The charge carrier densities were controlled by the SAM treatment in both dominant and non-dominant carrier-channel regimes. This work demonstrates that control of the charge carrier densities can be efficiently achieved by modifying the injection property with SAM treatment; thus, this approach can achieve polarity conversion of the OFETs.

We demonstrated highly efficient inverted bottom-emission organic light-emitting diodes (IBOLEDs) using tin dioxide (SnO2) nanoparticles (NPs) as an electron injection layer at the interface between the indium tin oxide (ITO) cathode and the organic electron transport layer. The SnO2 NP layer can facilitate the electron injection since the conduction band energy level of SnO2 NPs (-3.6 eV) is located between the work function of ITO (4.8 eV) and the lowest unoccupied molecular orbital (LUMO) energy level of typical electron transporting molecules (-2.5 to -3.5 eV). As a result, the IBOLEDs with the SnO2 NPs exhibited a decrease of the driving voltage by 7 V at 1000 cd/m(2) compared to the device without SnO2 NPs. They also showed a significantly enhanced luminous current efficiency of 51.1 cd/A (corresponds to the external quantum efficiency of 15.6%) at the same brightness, which is about two times higher values than that of the device without SnO2 NPs. We also measured the angular dependence of irradiance and electroluminescence (EL) spectra in the devices with SnO2 NPs and found that they had a nearly Lambertian emission profile and few shift in EL spectrum through the entire viewing angles, which are considered as remarkable and essential results for the application of OLEDs to display devices.