Feiyu Zhao

Position-dependent performance of copper phthalocyanine based field-effect transistors by gold nanoparticles modification

A facile fabrication and characteristics of copper phthalocyanine (CuPc)-based organic field-effect transistor (OFET) using the gold nanoparticles (Au NPs) modification is reported, thereby achieving highly improved performance. The effect of Au NPs located at three different positions, that is, at the SiO2/CuPc interface (device B), embedding in the middle of CuPc layer (device C), and on the top of CuPc layer (device D), is investigated, and the results show that device D has the best performance. Compared with the device without Au NPs (reference device A), device D displays an improvement of field-effect mobility (μ(sat)) from 1.65 × 10(-3) to 5.51 × 10(-3) cm(2) V(-1) s(-1), and threshold voltage decreases from -23.24 to -16.12 V. Therefore, a strategy for the performance improvement of the CuPc-based OFET with large field-effect mobility and saturation drain current is developed, on the basis of the concept of nanoscale Au modification. The model of an additional electron transport channel formation by FET operation at the Au NPs/CuPc interface is therefore proposed to explain the observed performance improvement. Optimum CuPc thickness is confirmed to be about 50 nm in the present study. The device-to-device uniformity and time stability are discussed for future application.

Ultrahigh near infrared photoresponsive organic field-effect transistors with lead phthalocyanine/C60 heterojunction on poly(vinyl alcohol) gate dielectric

Performances of photoresponsive organic field-effect transistors (photOFETs) operating in the near infrared (NIR) region utilizing SiO2 as the gate dielectric is generally low due to low carrier mobility of the channel. We report on NIR photOFETs based on lead phthalocyanine (PbPc)/C60 heterojunction with ultrahigh photoresponsivity by utilizing poly(vinyl alcohol) (PVA) as the gate dielectric. For 808 nm NIR illumination of 1.69 mW cm(-2), an ultrahigh photoresponsivity of 21 A W(-1), and an external quantum efficiency of 3230% were obtained at a gate voltage of 30 V and a drain voltage of 80 V, which are 124 times and 126 times as large as the reference device with SiO2 as the gate dielectric, respectively. The ultrahigh enhancement of photoresponsivity is resulted from the huge increase of electron mobility of C60 film grown on PVA dielectric. AFM investigations revealed that the C60 film grown on PVA is much smooth and uniform and the grain size is much larger than that grown on SiO2 dielectric, which together results in four orders of magnitude increase of the field-effect electron mobility of C60 film.

Toward high performance broad spectral hybrid organic–inorganic photodetectors based on multiple component organic bulk heterojunctions

Broadening the absorption bandwidth of photodetectors by incorporating multiple absorber materials to form bulk-heterojunction active layers is an attractive method of resolving the narrow absorption of organic semiconductors. Here we report the fabrication and characterization of broad spectral hybrid organic–inorganic photodetectors through an optimized multiple component organic bulk heterojunctions route. The study clearly shows that both the two-component and three-component photodetectors have ultrahigh photosensitivity and spectral uniformity of responsivity for visible to near-infrared light. Operating at room temperature, the three-component based photodetectors achieve ultrahigh photosensitivities of 30–50 A W−1 at ∼0.1 mW incident optical power, which are almost two orders of magnitude larger than commercial Si and InGaAs photodiodes. Also, this work demonstrates that the wide variation of optical absorption of multiple component organic bulk heterojunctions will provide a strategy to fabricate facile broadband photodetectors.

Ultrasensitive flexible broadband photodetectors achieving pA scale dark current

Organolead halide perovskite is a newly emerging low-cost, solution-processable material with a broadband absorption from the ultraviolet (UV) to visible (Vis) region, which has attracted a great deal of interest in high-performance optoelectronic devices. However, some practicable applications need a cover of UV–Vis–NIR region for photoelectric conversion, a task that remains a significant challenge for further extending the absorption toward the near-infrared radiation (NIR) region. Here, to the best of our knowledge, we prove for the first time an ultrasensitive flexible broadband photodetector based on porous organolead perovskite-phthalocyanine heterostructure, which combines the synergetic properties of high UV–Vis absorbance of perovskite with enhanced NIR absorption for triclinic lead phthalocyanine. The photosensitivity of the as-prepared devices reaches up to 104 at a low intensity of 10 mW cm−2, which is among the largest values reported for broadband photodetectors. Significantly, performed at room temperature, the device achieves a pA scale dark current along with an ultrafast response speed of less than 0.6 ms for as-adopted full spectra. Our results provide an easy and promising route to develop low-cost, flexible and highly sensitive UV–Vis–NIR photodetectors.Semiconductor physics: Energy saving flexible broadband hybrid photodetectorEnergy efficient and flexible alternative photodetector that detects both visible and invisible light comes closer to real life than ever. A group of researchers from China has developed an organic-inorganic hybrid photodetector that outperforms conventional inorganic like Si and InGaAs-based photodetectors in at least two aspects: broader detection spectral range and much lower dark current. Thanks to the structural flexibility of two hybrid photosensitive materials, methyl-ammonium lead halide and lead phthalocyanine, the team engineered the large area sub-micron thick photodetector with porous structures, which is the key to reducing the standby power consumption by more than 30 times compared to the best InGaAs and Si-based photodetectors. More importantly, the hybrid photodetector needs no additional apparatus or power to cool it for continuous operation, in contrast to the InGaAs photodetector.

Toward Ultrahigh Red Light Responsive Organic FETs Utilizing Neodymium Phthalocyanine as Light Sensitive Material

The performance of photoresponsive organic FETs (photOFETs) intimately depends on their optical absorption and charge carrier transport property. We report on red light responsive photOFETs based on various device structures utilizing neodymium phthalocyanine (NdPc2) as the light sensitive material. PhotOFETs based on planar heterojunction, bulk heterojunction (BHJ), and hybrid planar-BHJ (HPBHJ) with NdPc2 and C60 on poly(vinyl alcohol) (PVA) and SiO2 gate dielectric were fabricated and characterized. Among various device structures, HPBHJ-photOFET on PVA dielectric showed the best performance. For the 650-nm-red light illumination, an ultrahigh photoresponsivity of 108 A/W and a maximum photosensitivity of 3.75×104 were obtained. The ultrahigh enhancement of the photoresponsivity for HPBHJ-photOFET is resulted from high absorption coefficient of NdPc2 in the red light region, high dissociation efficiency of the photogenerated excitons, and high electron mobility of C60 layer grown on PVA.

Enhanced performance of isotype planar heterojunction photoresponsive organic field-effect transistors by using Ag source-drain electrodes

Pentacene/lead phthalocyanine (PbPc)-based isotype and fullerene /PbPc-based anisotype planar heterojunction near-infrared photoresponsive organic field-effect transistors (PhOFETs) were fabricated. We compared the performance of the isotype planar heterojunction PhOFET and the anisotype one, and dominantly investigated the effect of contact on the performance of the isotype planar heterojunction devices. The results showed that the isotype planar heterojunction device exhibits a comparable maximum photoresponsivity of 107 mA/W and a comparable maximum photo/dark current ratio of to the anisotype one ( of 109 mA/W and of ), and exhibits superior air stability to the anisotype one. Moreover, it is surprising to find that Ag source-drain electrodes replacing Au ones yield a performance enhancement in isotype PHJ devices, this is mainly because the use of Ag source-drain electrodes enhances the photo-generated exciton dissociation efficiency at the metal/PbPc interface.

A striking performance improvement of fullerene n-channel field-effect transistors via synergistic interfacial modifications

For fullerene based n-channel transistors, remarkably improved device characteristics were achieved via charge injection and transport interfacial synergistic modifications using low-cost aluminium source/drain electrodes. Compared with the reference device without any modifications (device A), the as-fabricated transistor (device H) showed a dramatic improvement of saturation mobility from 0.0026 to 0.3078 cm2 V−1 s−1 with a maximum on–off current ratio of 106 and a minimum subthreshold slope of 1.52 V decade−1. AFM and XRD analysis manifested that the deposited C60 films on PVA/OTS successive-modified SiO2 substrate were highly dense polycrystalline and uniform with larger crystalline grain and less grain boundary. A gap state assisted electron injection mechanism was proposed to explicate the enhanced electrical conductivity considering BCP modification for charge injection interface, which has been well corroborated by a diode-based injection experiment and a theoretical calculation of contact resistances. We further demonstrated the application of the concept modification method to enable comparative time-stable operation of fullerene n-channel transistors. Given many key merits, we believed that this general method using multi-interface modifications could be extended to fabricate other n-channel OFETs with superior electrical performance and stability.

Achieving Weak Light Response with Plasmonic Nanogold-Decorated Organic Phototransistors

Weak light response of organic photodetectors has fascinating potentials in fields of modern science and technology. However, their photoresponsivity is hindered by poor photocarrier excitation and transport. Decorating active-layer surface with plasmonic nanometals is considered a viable strategy to address this issue. Here, we demonstrate a plasmonic nanogold decorated organic phototransistor achieving remarkable enhancement of photoresponsivity. Meanwhile, the photoresponsive range is broadened by 4 orders of magnitude. The proposed design is substantiated by a schematic energy level model combined with theoretical simulation analysis, enabling the development of the advanced optoelectronics.