We fabricated a C fullerene-based molecular spin-photovoltaic device that integrates a photovoltaic response with the spin transport across the molecular layer. The photovoltaic response can be modified under the application of a small magnetic field, with a magnetophotovoltage of up to 5% at room temperature. Device functionalities include a magnetic current inverter and the presence of diverging magnetocurrent at certain illumination levels that could be useful for sensing. Completely spin-polarized currents can be created by balancing the external partially spin-polarized injection with the photogenerated carriers.

The semiconducting p-n junction is a simple device structure with great relevance for electronic and optoelectronic applications. The successful integration of low-dimensional materials in electronic circuits has opened the way forward for producing gate-tunable p-n junctions. In that context, we present here an organic (Cu-phthalocyanine)-2D layered material (MoS2) hybrid p-n junction with both gate-tunable diode characteristics and photovoltaic effect. Our proof-of-principle devices show multifunctional properties with diode rectifying factors of up to 10(4), while under light exposure they exhibit photoresponse with a measured external quantum efficiency of ∼11%. As for their photovoltaic properties, we found open circuit voltages of up to 0.6 V and optical-to-electrical power conversion efficiency of 0.7%. The extended catalogue of known organic semiconductors and two-dimensional materials offer the prospect for tailoring the properties and the performance of the resulting devices, making organic-2D p-n junctions promising candidates for future technological applications.

wileyonlinelibrary.comGraphene, [ 11 ] a one-atom thick zero band gap semiconductor has allowed the development of new electronic device schemes such as the graphene-barristor, [ 12 ] the graphene-vertical-fi eld-effecttransistor (VFET), [13][14][15][16] and the graphenebase hot electron transistor. [ 17 ] In organic electronics, graphene can be an ideal choice to use as the injector (or source) electrode for a VFET since its Fermi level, its corresponding work function and its available low density of states (DOS) [ 18 ] can all be easily modulated, providing a tunable energy barrier which eventually controls the device operation. In addition, the electric fi eld produced by a gate electrode will extend into the organic semiconductor, as the monolayer thickness of graphene is insuffi cient to fully screen it. [ 13,19 ] In order to increase the performance of organic thin fi lm transistors (OTFT) compared with the inorganic counterparts, a unique vertical architecture with a molecular semiconductor (C 60 ) was fi rst demonstrated using a thin and rough (with a roughness comparable to the thickness) metal electrode. [ 20 ] A clear advantage of the vertical over the lateral organic transistor geometry is that the channel length is controlled by the thickness of the organic layer and the devices can be downsized in both the lateral and the vertical directions. In the case of a perforated metallic source electrode, the electric fi eld can directly access the metal/organic interface which causes the energy level realignment (similar to the band bending in inorganic semiconductor) in the organic semiconductor. Although Ma and Yang have reported a large on/off current ratio (≈10 6 ), the high DOS and the fi xed work function of the metallic electrode (injector) limits its application to a few organic semiconductors. [ 20 ] Later on, Liu et al. introduced a carbon nanotube-based source electrode with low DOS in organic VFETs for a wide range of organic semiconductors. [ 21 ] Carbon nanotubes allow new mechanisms for transistor operation such as the tuning of the gate modulated energy barrier. Graphene, similar to carbon nanotubes in its electrical and mechanical properties, has additional advantages over them due to the large-scale availability (chemical vapor deposition (CVD)-grown graphene) of chemically inert high quality 2D surfaces. [ 14,22 ] On the other hand, fullerene (C 60 ) is one of the most widely studied molecular semiconductors [ 2,5,20,[23][24][25] and a common choice as an active media for transistors. C 60 has an energy gap ( E g = 1.7 eV), between its highest occupied molecular orbital Gate-Controlled Energy Barrier at a Graphene/Molecular Semiconductor JunctionSubir Parui , * Luca Pietrobon , David Ciudad , Saül Vélez , Xiangnan Sun , Fèlix Casanova , Pablo Stoliar , and Luis E. Hueso * The formation of an energy-barrier at a metal/molecular semiconductor junction is a universal phenomenon which limits the performance of many molecular semiconductor-based electronic devices, from fi eld-effect trans...

Energy barriers between the metal Fermi energy and the molecular levels of organic semiconductor devoted to charge transport play a fundamental role in the performance of organic electronic devices. Typically, techniques such as electron photoemission spectroscopy, Kelvin probe measurements, and in-device hot-electron spectroscopy have been applied to study these interfacial energy barriers. However, so far there has not been any direct method available for the determination of energy barriers at metal interfaces with n-type polymeric semiconductors. This study measures and compares metal/solution-processed electron-transporting polymer interface energy barriers by in-device hot-electron spectroscopy and ultraviolet photoemission spectroscopy. It not only demonstrates in-device hot-electron spectroscopy as a direct and reliable technique for these studies but also brings it closer to technological applications by working ex situ under ambient conditions. Moreover, this study determines that the contamination layer coming from air exposure does not play any significant role on the energy barrier alignment for charge transport. The theoretical model developed for this work confirms all the experimental observations.

We demonstrate a high-yield fabrication of non-local spin valve devices with roomtemperature spin lifetimes of up to 3 ns and spin relaxation lengths as long as 9 µm in platinum-based chemical vapor deposition (Pt-CVD) synthesized single-layer graphene on SiO 2 /Si substrates. The spin-lifetime systematically presents a marked minimum at the charge neutrality point, as typically observed in pristine exfoliated graphene.However, by studying the carrier density dependence beyond n ~ 5 x 10 12 cm -2 , via electrostatic gating, it is found that the spin lifetime reaches a maximum and then starts decreasing, a behavior that is reminiscent of that predicted when the spinrelaxation is driven by spin-orbit interaction. The spin lifetimes and relaxation lengths compare well with state-of-the-art results using exfoliated graphene on SiO 2 /Si, being a factor two-to-three larger than the best values reported at room temperature using the same substrate. As a result, the spin signal can be readily measured across 30-µm long graphene channels. These observations indicate that Pt-CVD graphene is a promising material for large-scale spin-based logic-in-memory applications.

Realizing an optimal Schottky interface of graphene on Si is challenging, as the electrical transport strongly depends on the graphene quality and the fabrication processes. Such interfaces are of increasing research interest for integration in diverse electronic devices as they are thermally and chemically stable in all environments, unlike standard metal/semiconductor interfaces. We fabricate such interfaces with n-type Si at ambient conditions and find their electrical characteristics to be highly rectifying, with minimal reverse leakage current (<10 −10 A) and rectification of more than 10 6 . We extract Schottky barrier height of 0.69 eV for the exfoliated graphene and 0.83 eV for the CVD graphene devices at room temperature. The temperature dependent electrical characteristics suggest the influence of inhomogeneities at the graphene/n-Si interface. A quantitative analysis of the inhomogeneity in Schottky barrier heights is presented using the potential fluctuation model proposed by Werner and Güttler.

Organic field-effect transistors (OFETs) are fundamental building blocks for plastic electronics such as organic photovoltaics or bendable displays with organic light emitting diodes, and radio-frequency identification (RFID) tags. A key part in the performance of OFET is the organic material constituting the channel. OFETs based on solution-processed polymers represent a new class of organic electronic devices. Recent developments in upscale solution-processed polymers have advanced towards high throughput, low-cost, and environmentally friendly materials for high-performance applications. Together with the integration of high performance materials, another enduring challenge in OFET development is the improvement and control of the injection of charge carriers. Graphene, a two-dimensional layer of covalently bonded carbon atoms, is steadily making progress into applications relying on van der Waals heterointerfaces with organic semiconductors. Here, we demonstrate the versatile operation of solution-processed organic transistors both in lateral and vertical geometries by exploiting the weak-screening effect and work function modulation properties of graphene electrodes. Our results demonstrate a general strategy for overcoming traditional noble metal electrodes and to integrate graphene with solution-processed Polyera ActiveInk™ N2200 polymer transistors for high-performance devices suitable for future plastic electronics.

Marcus’s theory of electron transfer, initially formulated six decades ago for redox reactions in solution, is now of great importance for very diverse scientific communities. The molecular scale tunability of electronic properties renders organic semiconductor materials in principle an ideal platform to test this theory. However, the demonstration of charge transfer in different Marcus regions requires a precise control over the driving force acting on the charge carriers. Here, we make use of a three-terminal hot-electron molecular transistor, which lets us access unconventional transport regimes. Thanks to the control of the injection energy of hot carriers in the molecular thin film we induce an effective negative differential resistance state that is a direct consequence of the Marcus Inverted Region.