Boron-Implanted Black Silicon Photodiode with Close-to-Ideal Responsivity from 200 to 1000 nm

Detection of UV light has traditionally been a major challenge for Si photodiodes due to reflectance losses and junction recombination. Here we overcome these problems by combining a nanostructured surface with an optimized implanted junction and compare the obtained performance to state-of-the-art commercial counterparts. We achieve a significant improvement in responsivity, reaching near ideal values at wavelengths all the way from 200 to 1000 nm. Dark current, detectivity, and rise time are in turn shown to be on a similar level. The presented detector design allows a highly sensitive operation over a wide wavelength range without making major compromises regarding the simplicity of the fabrication or other figures of merit relevant to photodiodes.

Low-Dimensional Metal Halide Perovskite Photodetectors

Metal halide perovskites (MHPs) have been a hot research topic due to their facile synthesis, excellent optical and optoelectronic properties, and record-breaking efficiency of corresponding optoelectronic devices. Nowadays, the development of miniaturized high-performance photodetectors (PDs) has been fueling the demand for novel photoactive materials, among which low-dimensional MHPs have attracted burgeoning research interest. In this report, the synthesis, properties, photodetection performance, and stability of low-dimensional MHPs, including 0D, 1D, 2D layered and nonlayered nanostructures, as well as their heterostructures are reviewed. Recent advances in the synthesis approaches of low-dimensional MHPs are summarized and the key concepts for understanding the optical and optoelectronic properties related to the PD applications of low-dimensional MHPs are introduced. More importantly, recent progress in novel PDs based on low-dimensional MHPs is presented, and strategies for improving the performance and stability of perovskite PDs are highlighted. By discussing recent advances, strategies, and existing challenges, this progress report provides perspectives on low-dimensional MHP-based PDs in the future.

Molecule-Based Transistors: From Macroscale to Single Molecule

Molecule-based field-effect transistors (FETs) are of great significance as they have a wide range of application prospects, such as logic operations, information storage and sensor monitoring. This account mainly introduces and reviews our recent work in molecular FETs. Specifically, through molecular and device design, we have systematically investigated the construction and performance of FETs from macroscale to nanoscale and even single molecule. In particular, we have proposed the broad concept of molecular FETs, whose functions can be achieved through various external controls, such as light stimulation, and other physical, chemical or biological interactions. In the end, we tend to focus the discussion on the development challenges of single-molecule FETs, and propose prospects for further breakthroughs in this field.

Highly stable and Pb-free bismuth-based perovskites for photodetector applications

Herein, we report synthesis of highly stable, Pb-free bismuth iodide, stoichiometric methylammonium bismuth iodide and non-stoichiometric methylammonium bismuth iodide perovskite thin films for photodetector applications.

High Responsivity and High Rejection Ratio of Self-Powered Solar-Blind Ultraviolet Photodetector Based on PEDOT:PSS/β-Ga2O3 Organic/Inorganic p-n Junction

A high responsivity self-powered solar-blind deep UV (DUV) photodetector with high rejection ratio was proposed based on inorganic/organic hybrid p-n junction. Owing to the high crystallized β-Ga₂O₃ and excellent transparent conductive polymer PEDOT:PSS, the device exhibited ultrahigh responsivity of 2.6 A/W at 245 nm with a sharp cutoff wavelength at 255 nm without any power supply. The responsivity is much larger than that of previous solar-blind DUV photodetectors. Moreover, the device exhibited an ultrahigh solar-blind/UV rejection ratio (R_245 nm/R_280 nm) of 10³, which is two orders of magnitude larger than the average value reported in Ga₂O₃-based solar-blind photodetectors. In addition, the photodetector shows a narrow bandpass response of only 17 nm in width. This work might be of great value in developing a high wavelength selective DUV photodetector with respect to low cost for future energy-efficient photoelectric devices.

Ultrathin Ruddlesden-Popper Perovskite Heterojunction for Sensitive Photodetection

Thanks to their unique optical and electric properties, 2D materials have attracted a lot of interest for optoelectronic applications. Here, the emerging 2D materials, organic-inorganic hybrid perovskites with van der Waals interlayer interaction (Ruddlesden-Popper perovskites), are synthesized and characterized. Photodetectors based on the few-layer Ruddlesden-Popper perovskite show good photoresponsivity as well as good detectivity. In order to further improve the photoresponse performance, 2D MoS₂ is chosen to construct the perovskite-MoS₂ heterojunction. The performance of the hybrid photodetector is largely improved with 6 and 2 orders of magnitude enhancement for photoresponsivity (10⁴ A W^-1 ) and detectivity (4 × 10¹⁰ Jones), respectively, which demonstrates the facile charge separation at the interface between perovskite and MoS₂ . Furthermore, the contribution of back gate tuning is proved with a greatly reduced dark current. The results demonstrated here will open up a new field for the investigation of 2D perovskites for optoelectronic applications.

Strategies toward High-Performance Solution-Processed Lateral Photodetectors

Due to their low cost and ease of integration, solution-processed lateral photodetectors (PDs) are becoming an important device type among the PD family. In recent years, enormous effort has been devoted to improving their performances, and great achievements have been made. A summary of the core progress, especially from the perspective of design principles and device physics, is necessary to further the development of the field, but is currently lacking. Here, to address this need, first, the working mechanism of PDs and the device figures-of-merit are introduced. Second, by classifying the active materials into four categories, including inorganic, organic, hybrid, and perovskite, the developed strategies toward high performance are discussed respectively. To close, the common physical rules behind all these strategies are generalized, and suggestions for future development are given accordingly.

Robust Piezo-Phototronic Effect in Multilayer γ-InSe for High-Performance Self-Powered Flexible Photodetectors

The piezo-phototronic effect has been promising as an effective means to improve the performance of two-dimensional (2D) semiconductor based optoelectronic devices. However, the current reported monolayer 2D semiconductors are not regarded as suitable for actual flexible piezotronic photodetectors due to their insufficient optical absorption and mechanical durability, although they possess strong piezoelectricity. In this work, we demonstrate that, unlike 2H-phase transition-metal dichalcogenides, γ-phase InSe with a hexagonal unit cell possesses broken inversion symmetry in all the layer numbers and has a strong second-harmonic generation effect. Moreover, driven by the piezo-phototronic effect, a flexible self-powered photodetector based on multilayer γ-InSe, which can work without any energy supply, is proposed. The device exhibited ultrahigh photon responsivity of 824 mA/W under light illuminations of 400 nm (0.368 mW/cm²). Moreover, the responsivity and response speed of this photodetector were enhanced further by as much as 696% and 1010%, respectively, when a 0.62% uniaxial tensile strain was applied. Our devices exhibit high reliability and stability during a 6 month test time. These significant findings offer a promising pathway to construct high-performance flexible piezo-phototronic photodetectors based on multilayer 2D semiconductors.

Perovskite/Black Phosphorus/MoS2 Photogate Reversed Photodiodes with Ultrahigh Light On/Off Ratio and Fast Response

As compared with epitaxial semiconductor devices, two-dimensional (2D) heterostructures offer alternative facile platforms for many optoelectronic devices. Among them, photovoltaic based photodetectors can give fast response, while the photogate devices can lead to high responsivity. Here, we report a 2D photogate photodiode, which combines the benefits of 2D black phosphorus/MoS₂ photodiodes with the emerging potential of perovskite, to achieve both fast response and high responsivity. This device architecture is constructed based on the fast photovoltaic operation together with the high-gain photogating effect. Under reverse bias condition, the device exhibits high responsivity (11 A/W), impressive detectivity (1.3 × 10¹² Jones), fast response (150/240 μs), and low dark current (3 × 10^-11 A). All these results are already much better in nearly all aspects of performance than the previously reported 2D photodiodes operating in reverse bias, achieving the optimal balance between all figure-of-merits. Importantly, with a zero bias, the device can also yield high detectivity (3 × 10¹¹ Jones), ultrahigh light on/off ratio (3 × 10⁷), and extremely high external quantum efficiency (80%). This device architecture thus has a promise for high-efficiency photodetection and photovoltaic energy conversion.

Ultrasensitive 2D Bi2 O2 Se Phototransistors on Silicon Substrates

2D materials are considered as intriguing building blocks for next-generation optoelectronic devices. However, their photoresponse performance still needs to be improved for practical applications. Here, ultrasensitive 2D phototransistors are reported employing chemical vapor deposition (CVD)-grown 2D Bi₂ O₂ Se transferred onto silicon substrates with a noncorrosive transfer method. The as-transferred Bi₂ O₂ Se preserves high quality in contrast to the serious quality degradation in hydrofluoric-acid-assisted transfer. The phototransistors show a responsivity of 3.5 × 10⁴ A W^-1 , a photoconductive gain of more than 10⁴ , and a time response in the order of sub-millisecond. With back gating of the silicon substrate, the dark current can be reduced to several pA. This yields an ultrahigh sensitivity with a specific detectivity of 9.0 × 10¹³ Jones, which is one of the highest values among 2D material photodetectors and two orders of magnitude higher than that of other CVD-grown 2D materials. The high performance of the phototransistor shown here together with the developed unique transfer technique are promising for the development of novel 2D-material-based optoelectronic applications as well as integrating with state-of-the-art silicon photonic and electronic technologies.

A Dual-Band Multilayer InSe Self-Powered Photodetector with High Performance Induced by Surface Plasmon Resonance and Asymmetric Schottky Junction

A dual-band self-powered photodetector (SPPD) with high sensitivity is realized by a facile combination of InSe Schottky diode and Au plasmonic nanoparticle (NP) arrays. Comparing with pristine InSe devices, InSe/Au photodetectors possess an additional capability of photodetection in visible to near-infrared (NIR) region. This intriguing phenomenon is attributed to the wavelength selective enhancement of pristine responsivities by hybridized quadrupole plasmons resonance of Au NPs. It is worth pointing out that the maximum of enhancement ratio in responsivity reaches up to ∼1200% at a wavelength of 685 nm. In addition, owing to a large Schottky barrier difference formed between active layer and two asymmetric electrodes, the responsivities of dual-band InSe/Au photodetector could reach up to 369 and 244 mA/W at the wavelength of 365 and 685 nm under zero bias voltage, respectively. This work would provide an additional opportunity for developing multifunctional photodetectors with high performance based on two-dimensional materials, upgrading their capacity of photodetection in a complex environment.

Halide Perovskite Nanopillar Photodetector

Numerous studies have reported the use of halide perovskites as highly functional light-harvesting materials. The development of optimized compositions and deposition approaches has led to impressive improvements; however, no noticeable breakthrough in performance has been observed for these materials recently. Here, a breakthrough that enables the fabrication of vertically grown halide perovskite (VGHP) nanopillar photodetectors via a nanoimprinting crystallization technique is demonstrated. We used engraved nanopatterned polymer stamps to form VGHP nanopillars during the pressurized crystallization of the softly baked gel state of a methylammonium lead iodide (CH₃NH₃PbI₃, denoted MAPI) film. The VGHP films exhibit much lower defect density and higher conductivity, as supported by current-voltage characteristic measurements and conductive atomic force microscopy measurements. Ultimately, two-terminal lateral photodetectors based on the VGHP nanopillar films show a greatly enhanced photoresponse compared with flat film-based photodetectors. We expect that the deposition method presented here will help surpass the technical limits and contribute to further improvements in various halide-perovskite-based devices.

Switching Effects in Molecular Electronic Devices

The creation of molecular electronic switches by using smart molecules is of great importance to the field of molecular electronics. This requires a fundamental understanding of the intrinsic electron transport mechanisms, which depend on several factors including the charge transport pathway, the molecule-electrode coupling strength, the energy of the molecular frontier orbitals, and the electron spin state. On the basis of significant progresses achieved in both experiments and theory over the past decade, in this review article we focus on new insights into the design and fabrication of different molecular switches and the corresponding switching effects, which is crucial to the development of molecular electronics. We summarize the strategies developed for single-molecule device fabrication and the mechanism of these switching effects. These analyses should be valuable for deeply understanding the switching effects in molecular electronic devices.

Novel UV-Visible Photodetector in Photovoltaic Mode with Fast Response and Ultrahigh Photosensitivity Employing Se/TiO2 Nanotubes Heterojunction

A feasible strategy for hybrid photodetector by integrating an array of self-ordered TiO₂ nanotubes (NTs) and selenium is demonstrated to break the compromise between the responsivity and response speed. Novel heterojunction between the TiO₂ NTs and Se in combination with the surface trap states at TiO₂ help regulate the electron transport and facilitate the separation of photogenerated electron-hole pairs under photovoltaic mode (at zero bias), leading to a high responsivity of ≈100 mA W^-1 at 620 nm light illumination and the ultrashort rise/decay time (1.4/7.8 ms). The implanting of intrinsic p-type Se into TiO₂ NTs broadens the detection range to UV-visible (280-700 nm) with a large detectivity of over 10¹² Jones and a high linear dynamic range of over 80 dB. In addition, a maximum photocurrent of ≈10⁷ A is achieved at 450 nm light illumination and an ultrahigh photosensitivity (on/off ratio up to 10⁴ ) under zero bias upon UV and visible light illumination is readily achieved. The concept of employing novel heterojunction geometry holds great potential to pave a new way to realize high performance and energy-efficient optoelectronic devices for practical applications.

Scalable-Production, Self-Powered TiO2 Nanowell-Organic Hybrid UV Photodetectors with Tunable Performances

Hybrid inorganic-organic photoelectric devices draw considerable attention because of their unique features by combining the tunable functionality of organic molecules and the superior intrinsic carrier mobilities of inorganic semiconductors. An ordered thin layer of TiO₂ nanowells is formed in situ with shallow nanoconcave patterns without cracking with scalable production by a facile and economic strategy, and these layers are used as building blocks to construct hybrid UV photodetectors (PDs). Organic conducting polymers (polyaniline (PANI) with various morphologies) have been exploited as p-type materials, enabling tunable photodetection performances at zero bias. The thin layer of n-type TiO₂ nanowells is favorable for electron transport and light absorption with respect to their conventional nanotubular counterparts, while PANI acts as a hopping state or bridge to largely enhance the transition probability of the valence electrons in TiO₂ to its conduction band, resulting in an increase in photocurrent in a self-powered mode. In particular, the lowest polyaniline loading sample (TP1) exhibits the highest responsivity (3.6 mA·W^-1), largest on-off switching ratio (∼10³), excellent wavelength selectivity, fast response speed (3.8/30.7 ms), and good stability under 320 nm light illumination (0.56 mW·cm^-2) without an external energy supply. This work might be of great value in developing tunable UV photoresponse materials with respect to low cost and a large area for future energy-efficient optoelectronic devices.

Ultrasensitive Self-Powered Solar-Blind Deep-Ultraviolet Photodetector Based on All-Solid-State Polyaniline/MgZnO Bilayer

A high sensitivity self-powered solar-blind photodetector is successfully constructed based on the polyaniline/MgZnO bilayer. The maximum responsivity of the photodetector is 160 μA W^-1 at 250 nm under 0 V bias. The device also exhibits a high on/off ratio of ≈10⁴ under 250 nm illumination at a relatively weak light intensity of 130 μW cm^-2 without any power.

Carbon Electrode-Molecule Junctions: A Reliable Platform for Molecular Electronics

The development of reliable approaches to integrate individual or a small collection of molecules into electrical nanocircuits, often termed "molecular electronics", is currently a research focus because it can not only overcome the increasing difficulties and fundamental limitations of miniaturization of current silicon-based electronic devices, but can also enable us to probe and understand the intrinsic properties of materials at the atomic- and/or molecular-length scale. This development might also lead to direct observation of novel effects and fundamental discovery of physical phenomena that are not accessible by traditional materials or approaches. Therefore, researchers from a variety of backgrounds have been devoting great effort to this objective, which has started to move beyond simple descriptions of charge transport and branch out in different directions, reflecting the interdisciplinarity. This Account exemplifies our ongoing interest and great effort in developing efficient lithographic methodologies capable of creating molecular electronic devices through the combination of top-down micro/nanofabrication with bottom-up molecular assembly. These devices use nanogapped carbon nanomaterials (such as single-walled carbon nanotubes (SWCNTs) and graphene), with a particular focus on graphene, as point contacts formed by electron beam lithography and precise oxygen plasma etching. Through robust amide linkages, functional molecular bridges terminated with diamine moieties are covalently wired into the carboxylic acid-functionalized nanogaps to form stable carbon electrode-molecule junctions with desired functionalities. At the macroscopic level, to improve the contact interface between electrodes and organic semiconductors and lower Schottky barriers, we used SWCNTs and graphene as efficient electrodes to explore the intrinsic properties of organic thin films, and then build functional high-performance organic nanotransistors with ultrahigh responsivities. At the molecular level, to form robust covalent bonds between electrodes and molecules and improve device stability, we developed a reliable system to immobilize individual molecules within a nanoscale gap of either SWCNTs or graphene through covalent amide bond formation, thus affording two classes of carbon electrode-molecule single-molecule junctions. One unique feature of these devices is the fact that they contain only one or two molecules as conductive elements, thus forming the basis for building new classes of chemo/biosensors with ultrahigh sensitivity. We have used these approaches to reveal the dependence of the charge transport of individual metallo-DNA duplexes on π-stacking integrity, and fabricate molecular devices capable of realizing label-free, real-time electrical detection of biological interactions at the single-event level, or switching their molecular conductance upon exposure to external stimuli, such as ion, pH, and light. These investigations highlight the unique advantages and importance of these universal methodologies to produce functional carbon electrode-molecule junctions in current and future researches toward the development of practical molecular devices, thus offering a reliable platform for molecular electronics and the promise of a new generation of multifunctional integrated circuits and sensors.

Ultrahigh Photogain Nanoscale Hybrid Photodetectors

A class of ultrasensitive nanoscale hybrid photodetectors formed from carbon electrode-molecule junctions using P3HT:PCBM as photoresponsive semiconductors are demonstrated. The unique device architecture, tunability of nanoscale channel lengths and the optimized contact nature of semiconductor/electrode interfaces led to ultrahigh photogains of 1000 with graphene nanoelectrodes and 1 000 000 with single-walled carbon nanotube nanoelectrodes.

Solar-Blind Avalanche Photodetector Based On Single ZnO-Ga₂O₃ Core-Shell Microwire

High-performance solar-blind (200-280 nm) avalanche photodetectors (APDs) were fabricated based on highly crystallized ZnO-Ga2O3 core-shell microwires. The responsivity can reach up to 1.3 × 10(3) A/W under -6 V bias. Moreover, the corresponding detectivity was as high as 9.91 × 10(14) cm·Hz(1/2)/W. The device also showed a fast response, with a rise time shorter than 20 μs and a decay time of 42 μs. The quality of the detectors in solar-blind waveband is comparable to or even higher than that of commercial Si APD (APD120A2 from Thorlabs Inc.), with a responsivity ∼8 A/W, detectivity ∼10(12) cm·Hz(1/2)/W, and response time ∼20 ns. The high performance of this APD make it highly suitable for practical applications as solar-blind photodetectors, and this core-shell microstructure heterojunction design method would provide a new approach for realizing an APD device.

High-performance perovskite-graphene hybrid photodetector

A high-performance novel photodetector is demonstrated, which consists of graphene and CH3 NH3 PbI3 perovskite layers. The resulting hybrid photodetector exhibits a dramatically enhanced photo responsivity (180 A/W) and effective quantum efficiency (5× 10(4) %) over a broad bandwidth within the UV and visible ranges.

Ultrahigh responsivity and external quantum efficiency of an ultraviolet-light photodetector based on a single VO₂ microwire

We demonstrated a single microwire photodetector first made using a VO2 microwire that exhibted high responsivity (Rλ) and external quantum efficiency (EQE) under varying light intensities. The VO2 nanowires/microwires were grown and attached on the surface of the SiO2/Si(100) substrate. The SiO2 layer can produce extremely low densities of long VO2 microwires. An individual VO2 microwire was bonded onto the ends using silver paste to fabricate a photodetector. The high-resolution transmission electron microscopy image indicates that the nanowires grew along the [100] axis as a single crystal. The critical parameters, such as Rλ, EQE, and detectivity, are extremely high, 7069 A W(-1), 2.4 × 10(10)%, and 1.5 × 10(14) Jones, respectively, under a bias of 4 V and an illumination intensity of 1 μW cm(-2). The asymmetry in the I-V curves results from the unequal barrier heights at the two contacts. The photodetector has a linear I-V curve with a low dark current while a nonlinear curves was observed under varing light intensities. The highly efficient hole-trapping effect contributed to the high responsivity and external quantum efficiency in the metal-oxide nanomaterial photodetector. The responsivity of VO2 photodetector is 6 and 4 orders higher than that of graphene (or MoS2) and GaS, respectively. The findings demonstrate that VO2 nanowire/microwire is highly suitable for realizing a high-performance photodetector on a SiO2/Si substrate.

Carbon nanotube electrodes in organic transistors

The scope of this Minireview is to provide an overview of the recent progress on carbon nanotube electrodes applied to organic thin film transistors. After an introduction on the general aspects of the charge injection processes at various electrode-semiconductor interfaces, we discuss the great potential of carbon nanotube electrodes for organic thin film transistors and the recent achievements in the field.

Selective synthesis of Sb2S3 nanoneedles and nanoflowers for high performance rigid and flexible photodetectors

Needle-like and flower-like antimony sulfide nanostructures were synthesized and applied for both rigid and flexible photodetectors. Rigid photodetectors based on both nanostructures have the features of linear photocurrent characteristics, low linear dynamic range and good sensitivity to light intensity. Especially, the rigid Sb2S3 nanoflowers photodetector has high photoresponse characteristics and its response time and decay time were found to be relatively fast as 6 ms and 10 ms respectively. The flexible Sb2S3 nanoflowers photodetector has high flexible, light-weight and adequate bendability with a response time of about 0.09 s and recovery time of 0.27 s. Our results revealed that the rigid and flexible photodetectors based on Sb2S3 nanostructures have great potential in next generation optoelectronic devices.

Unique role of self-assembled monolayers in carbon nanomaterial-based field-effect transistors

Molecular self-assembly is a promising technology for creating reliable functional films in optoelectronic devices with full control of thickness and even spatial resolution. In particular, rationally designed self-assembled monolayers (SAMs) play an important role in modifying the electrode/semiconductor and semiconductor/dielectric interfaces in field-effect transistors. Carbon nanomaterials, especially single-walled carbon nanotubes and graphene, have attracted intense interest in recent years due to their remarkable physicochemical properties. The combination of the advantages of both SAMs and carbon nanomaterials has been opening up a thriving research field. In this Review article, the unique role of SAMs acting as either active or auxiliary layers in carbon nanomaterials-based field-effect transistors is highlighted for tuning the substrate effect, controlling the carrier type and density in the conducting channel, and even installing new functionalities. The combination of molecular self-assembly and molecular engineering with materials fabrication could incorporate diverse molecular functionalities into electrical nanocircuits, thus speeding the development of nanometer/molecular electronics in the future.

Highly responsive ultrathin GaS nanosheet photodetectors on rigid and flexible substrates

The first GaS nanosheet-based photodetectors are demonstrated on both mechanically rigid and flexible substrates. Highly crystalline, exfoliated GaS nanosheets are promising for optoelectronics due to strong absorption in the UV-visible wavelength region. Photocurrent measurements of GaS nanosheet photodetectors made on SiO2/Si substrates and flexible polyethylene terephthalate (PET) substrates exhibit a photoresponsivity at 254 nm up to 4.2 AW(-1) and 19.2 AW(-1), respectively, which exceeds that of graphene, MoS2, or other 2D material-based devices. Additionally, the linear dynamic range of the devices on SiO2/Si and PET substrates are 97.7 dB and 78.73 dB, respectively. Both surpass that of currently exploited InGaAs photodetectors (66 dB). Theoretical modeling of the electronic structures indicates that the reduction of the effective mass at the valence band maximum (VBM) with decreasing sheet thickness enhances the carrier mobility of the GaS nanosheets, contributing to the high photocurrents. Double-peak VBMs are theoretically predicted for ultrathin GaS nanosheets (thickness less than five monolayers), which is found to promote photon absorption. These theoretical and experimental results show that GaS nanosheets are promising materials for high-performance photodetectors on both conventional silicon and flexible substrates.

Synthesis of few-layer GaSe nanosheets for high performance photodetectors

Two-dimensional (2D) semiconductor nanomaterials hold great promises for future electronics and optics. In this paper, a 2D nanosheets of ultrathin GaSe has been prepared by using mechanical cleavage and solvent exfoliation method. Single- and few-layer GaSe nanosheets are exfoliated on an SiO(2)/Si substrate and characterized by atomic force microscopy and Raman spectroscopy. Ultrathin GaSe-based photodetector shows a fast response of 0.02 s, high responsivity of 2.8 AW(-1) and high external quantum efficiency of 1367% at 254 nm, indicating that the two-dimensional nanostructure of GaSe is a new promising material for high performance photodetectors.

Interface engineering of semiconductor/dielectric heterojunctions toward functional organic thin-film transistors

Interface modification is an effective and promising route for developing functional organic field-effect transistors (OFETs). In this context, however, researchers have not created a reliable method of functionalizing the interfaces existing in OFETs, although this has been crucial for the technological development of high-performance CMOS circuits. Here, we demonstrate a novel approach that enables us to reversibly photocontrol the carrier density at the interface by using photochromic spiropyran (SP) self-assembled monolayers (SAMs) sandwiched between active semiconductors and gate insulators. Reversible changes in dipole moment of SPs in SAMs triggered by lights with different wavelengths produce two distinct built-in electric fields on the OFET that can modulate the channel conductance and consequently threshold voltage values, thus leading to a low-cost noninvasive memory device. This concept of interface functionalization offers attractive new prospects for the development of organic electronic devices with tailored electronic and other properties.