Major growth in the image sensor market is largely as a result of the expansion of digital imaging into cameras, whether stand-alone or integrated within smart cellular phones or automotive vehicles. Applications in biomedicine, education, environmental monitoring, optical communications, pharmaceutics and machine vision are also driving the development of imaging technologies. Organic photodiodes (OPDs) are now being investigated for existing imaging technologies, as their properties make them interesting candidates for these applications. OPDs offer cheaper processing methods, devices that are light, flexible and compatible with large (or small) areas, and the ability to tune the photophysical and optoelectronic properties − both at a material and device level. Although the concept of OPDs has been around for some time, it is only relatively recently that significant progress has been made, with their performance now reaching the point that they are beginning to rival their inorganic counterparts in a number of performance criteria including the linear dynamic range, detectivity, and color selectivity. This review covers the progress made in the OPD field, describing their development as well as the challenges and opportunities.

Organic Photodiodes: The Future of Full Color Detection and Image Sensing

Recently, graphene has been extensively researched in fundamental science and engineering fields and has been developed for various electronic applications in emerging technologies owing to its outstanding material properties, including superior electronic, thermal, optical and mechanical properties. Thus, graphene has enabled substantial progress in the development of the current electronic systems. Here, we introduce the most important electronic and thermal properties of graphene, including its high conductivity, quantum Hall effect, Dirac fermions, high Seebeck coefficient and thermoelectric effects. We also present up-to-date graphene-based applications: optical devices, electronic and thermal sensors, and energy management systems. These applications pave the way for advanced biomedical engineering, reliable human therapy, and environmental protection. In this review, we show that the development of graphene suggests substantial improvements in current electronic technologies and applications in healthcare systems.

Electronic and Thermal Properties of Graphene and Recent Advances in Graphene Based Electronics Applications

Flexible electronic devices have attracted a great deal of attention in recent years due to their flexibility, reduced complexity and lightweight. Such devices can conformably attach themselves to any bendable surface and can possess diverse transduction mechanisms. Consequently, with continued emphasis on innovation and development, major technological breakthroughs have been achieved in this area. This review focuses on the advancements of using organic field-effect transistors (OFETs) in flexible electronic applications in the past 10 years. In addition, to the above mentioned features, OFETs have multiple advantages such as low-cost, readout integration, large-area coverage, and power efficiency, which yield synergy. To begin with, we have introduced organic semiconductors (OSCs), followed by their applications in various device configurations and their mechanisms. Later, the use of OFETs in flexible sensor applications is detailed with multiple examples. Special attention is paid to discussing the effects induced on physical parameters of OFETs with respect to variations in external stimuli. The final section provides an outlook on the mechanical aspects of OSCs, activation and revival processes of sensory layers, small area analysis, and pattern recognition techniques for electronic devices.

Organic field-effect transistor-based flexible sensors

This review is focused on new concepts and recent progress in the development of three major quantum dot (QD) based optoelectronic devices: photovoltaic cells, photodetectors and LEDs In each application, we discuss recent champion devices with a range of architectures and discuss in detail the chronological steps taken to produce significant improvements in efficiency We consider this relative to developments in colloidal quantum dots and their effects on these devices, covering alloyed, doped and core/shell QDs, quaternary Cu–Zn–In–S QDs, graphene and silicon QDs, and the wide range of highly promising NIR QDs The diverse range of novel device designs is examined, including all-quantum dot devices, ternary hybrid compounds, plasmonic enhancements, and nano-heterojunction architectures In addition, we analyse recent advances in charge transport layers, blocking layers, nanostructured photoanode fabrication and the importance of QD surface treatments Throughout, we emphasise the use of hybrid composite materials including combinations of QDs with metal oxides, plasmonic nanoparticles, graphene and others Finally, this review provides an analysis of prospects of these important selected quantum dot-based optoelectronic devices

Colloidal quantum dots for optoelectronics

Ultrathin SnS nanobelts were synthesized via physical vapor deposition (PVD). Furthermore, high performance near-infrared (NIR) photodetectors based on SnS nanobelts showed an excellent photoresponsivity of 300 A W−1 under 800 nm light illumination with an external quantum efficiency of 4.65 × 104% and a detectivity of 6 × 109 Jones, as well as fast rise and decay times (τrise = 36 ms and τdecay = 7 ms), suggesting a promising future for the utilization of the SnS nanobelts in practical NIR light sensors.

High performance near-infrared photodetectors based on ultrathin SnS nanobelts grown via physical vapor deposition

A solution-processed near-infrared (NIR) photodetector based on PbSe colloidal quantum dots (CQDs) with a field-effect transistor (FET) configuration was presented. By blending PbSe CQDs into poly(3-hexylthiophene-2, 5-diyl) (P3HT) as active layer, the photosensitive spectrum of P3HT:PbSe nanocomposites extends into the NIR region. The responsivity and the specific detectivity of FET-based photodetector Au(gate)/PMMA (930nm)/P3HT:PbSe(55nm)/Au(source, drain) reached 500 A/W and $5.02 \times 10^{12}$ Jones, respectively, at $V_{\rm DS}=-40$ V and $V_{\rm G}=-40$ V with 40 mW/cm $^{2}$ of 980-nm laser illumination. It gets more stable due to its reverse fabrication using the dielectric layer to cover the active layer from environment air.

Solution-Processed PbSe Colloidal Quantum Dot-Based Near-Infrared Photodetector

Colloidal quantum dots (CQDs) are promising materials for flexible electronics, light sensing and energy conversion. In particular, as a narrow bandgap semiconductor, lead selenide (PbSe) CQDs have attracted considerable interest due to their potential applications in infrared (IR) optoelectronics such as IR light-emitting diodes (LEDs), photodetectors and solar cells. Solution-processed photodetectors are more attractive owing to their flexible, large-scale and low-cost fabrication, and their performance depends greatly on the film quality and surface morphology. In this study, a high performance solution-processed infrared photodetector based on PbSe CQDs blended with low hole mobility polymer poly(N-vinylcarbazole) (PVK) is presented. In order to obtain a higher device performance, different volume ratios (K = VPVK/VPbSe) of PVK (20 mg ml−1 in chloroform) in PbSe CQDs (15 mg ml−1 in chlorobenzene) were investigated, and a maximum responsivity and specific detectivity of 2.93 A W−1 and 1.24 × 1012 jones, respectively, were obtained at VG = −20 V under 30 mW cm−2 980 nm laser illumination for field-effect transistor (FET)-based photodetector Au(S&D)/PbSe : PVK/PMMA/Al(G), in which PbSe : PVK nanocomposite with K = 1 : 2 acts as the active layer and poly (methyl methacrylate) (PMMA) as the dielectric layer. The reasons for the high device performance of PbSe : PVK nanocomposite as an active layer are discussed, in which PbSe nanoparticles were blended with low hole mobility polymer PVK but showed comparable detectivity as that blended with regioregular P3HT. Moreover, all these types of photodetectors are very stable for reverse fabrication using PMMA dielectric layer to shield the active layer from the environment and by inorganic ligand exchange treatment on the active layer.

High performance solution-processed infrared photodetector based on PbSe quantum dots doped with low carrier mobility polymer poly(N-vinylcarbazole)

Electrical and detection performances of pentacene-based photodetector with vertical field-effect transistor (VFET) configuration were investigated in full visible region. By comparing with planar FET-based photodetector ITO/ PMMA(520 nm)/Pentacene(35 nm)/Au, the VFET-based photo-detector ITO/Pentacene(80 nm)/Al(15 nm)/Pentacene(80 nm)/ Au exhibits better performance. At an output current of ca. $-8\times 10^{-7}$ A, the threshold voltage ( $V_{\rm th}$ ) was −0.61 V for the VFET-based device at $V_{\mathrm {DS}} = -2$ V, but $V_{\mathrm {th}} = -7.1$ V for the planar one at $V_{\mathrm {DS}} = -12$ V. The performance of photodetectors depends on incident monochromatic light, and the VFET-based photodetector showed a maximum responsivity of 188 mA/W and a photosensitivity peak of 588 under 350-nm light, which were $\sim 11.75$ and 2.83 times as that of the planar one, respectively. Therefore, it provides an easy way to get the VFET-based organic photodetectors in full visible region with excellent photosensitivity, responsivity, and light selectivity, showing its promising application in all-organic image sensors working at low voltages.

Pentacene-Based Photodetector in Visible Region With Vertical Field-Effect Transistor Configuration

Infrared (IR) emission lead selenide (PbSe) quantum dots (QDs) have gained considerable attention in the last decade due to their potential applications in optoelectronic devices. However, the comprehensive applications of PbSe QDs have not been realized yet due to their high susceptibility to oxidation in air. In this paper, we demonstrate the stability enhancement of PbSe colloidal QDs via a post-synthetic ammonium chloride treatment and its applications in a solution-processed high-performance IR photodetector with a field-effect transistor (FET) configuration by reversely fabricating the PbSe active layer and polymethylmethacrylate (PMMA) dielectric layer. The responsivity and the specific detectivity of the FET-based photodetector Au(source, drain)/PbSe(52 nm)/PMMA(930 nm)/Au(gate) reached 64.17 mA W(-1) and 5.08 × 10(10) Jones, respectively, under 980 nm laser illumination with an intensity of 0.1 mW cm(-2). Therefore, it provides a promising way to make a high-sensitivity near-IR/mid-IR photodetector.

https://iopscience.iop.org/article/10.1088/0957-4484/27/6/065201/pdf

Stability enhancement of PbSe quantum dots via post-synthetic ammonium chloride treatment for a high-performance infrared photodetector.

In this paper, the influence of the active layer nanomorphology on device performance for ternary PbS(x)Se(1-x) quantum dot-based solution-processed infrared photodetector is presented. Firstly, ternary PbS(x)Se(1-x) quantum dots (QDs) in various chemical composition were synthesized and the bandgap of the ternary PbS(x)Se(1-x) QDs can be controlled by the component ratio of S/(S + Se), and then field-effect transistor (FET) based photodetectors Au/PbS0.4Se0.6:P3HT/PMMA/Al, in which ternary PbS0.4Se0.6 QDs doped with poly(3-hexylthiophene) (P3HT) act as the active layer and poly(methyl methacrylate) (PMMA) as the dielectric layer, were presented. By changing the weight ratio of P3HT to PbS0.4Se0.6 QDs (K = M(P3HT):M(QDs)) in dichlorobenzene solution, we found that the device with K = 2:1 shows optimal electrical property in dark; however, the device with K = 1:2 demonstrated optimal performance under illumination, showing a maximum responsivity and specific detectivity of 55.98 mA W(-1) and 1.02 × 10(10) Jones, respectively, at low V(DS) = -10 V and V(G) = 3 V under 980 nm laser with an illumination intensity of 0.1 mW cm(-2). By measuring the atomic force microscopy phase images of PbS0.4Se0.6:P3HT films in different weight ratio K, our experimental data show that the active layer nanomorphology has a great influence on the device performance. Also, it provides an easy way to fabricate high performance solution-processed infrared photodetector.

https://iopscience.iop.org/article/10.1088/0957-4484/27/16/165202/pdf

Influence of the active layer nanomorphology on device performance for ternary PbS(x)Se(1-x) quantum dots based solution-processed infrared photodetector.

Chunjie Fu

Papers

Solution-Processed PbSe Colloidal Quantum Dot-Based Near-Infrared Photodetector

High performance solution-processed infrared photodetector based on PbSe quantum dots doped with low carrier mobility polymer poly(N-vinylcarbazole)

Pentacene-Based Photodetector in Visible Region With Vertical Field-Effect Transistor Configuration

Stability enhancement of PbSe quantum dots via post-synthetic ammonium chloride treatment for a high-performance infrared photodetector.

Influence of the active layer nanomorphology on device performance for ternary PbS(x)Se(1-x) quantum dots based solution-processed infrared photodetector.