Anamika Dey

High-performance n-channel organic thin-film transistor based on naphthalene diimide.

A conjugated molecule comprising 1,4,5,8-naphthalene diimide (NDI) substituted with two octadecylamine (OD) chains has been synthesized (NDI-OD2) in a single step from commercial materials, and its organic thin-film transistor (OTFT) devices on glass substrate have been studied using poly(vinyl alcohol) (PVA) gate dielectric material. Although we utilized the PVA dielectric without any intermediate buffer layer or PVA cross-linkers, excellent electron mobility as high as ∼1.0 cm(2)V(-1) s(-1) are obtained. This NDI-OD2 molecule exhibits comparable optical (Eg(UV) ∼3.1 eV) and electrochemical band gaps (Eg(CV) ∼3.02 eV) with a lowest unoccupied molecular orbital (LUMO) energy levels of ∼3.3 eV. When processed by solution method, this material forms rod-shaped crystalline microstructures, whereas, when thermally deposited, it assumes the formation of smooth 2D films. The chemical as well as physical properties and theoretical calculations of NDI-OD2 have been studied and the effect of the C-18 alkyl chain unit has been discussed. The OTFT consisting of NDI-OD2 exhibits excellent performance parameters such as high electron mobility (μe) and Ion-to-Ioff ratio. After demonstrating the high performance of NDI-OD2-based TFT devices fabricated with biocompatible PVA dielectric, we have also demonstrated that these devices can be degraded because of the presence of this PVA dielectric when exposed to a high-moisture environment. The systematic degradation of the device activity in a controlled way within 10 days of exposure (>80% moisture) is also presented here. In this study, a conceptually important feature and futuristic aspect that the n-channel TFT devices can also be biodegraded irreversibly is demonstrated. This concept of developing a low cost and biodegradable OTFT device with biocompatible PVA dielectric with excellent electron mobility is expected to have diverse applications in disposable electronic tags, biomedical devices, and food industry packing.

Effect of Dual Cathode Buffer Layer on the Charge Carrier Dynamics of rrP3HT:PCBM Based Bulk Heterojunction Solar Cell

In bulk heterojunction (BHJ) solar cells, the buffer layer plays a vital role in enhancing the power conversion efficiency (PCE) by improving the charge carrier dynamics. A comprehensive understanding of the contacts is especially essential in order to optimize the performance of organic solar cells (OSCs). Although there are several fundamental reports on this subject, a proper correlation of the physical processes with experimental evidence at the photoactive layer and contact materials is essential. In this work, we incorporated three different additional buffer layers, namely, tris(8-hydroxyquinolinato) aluminum (Alq3), bathophenanthroline (BPhen) or bathocuproine (BCP) with LiF/Al as conventional cathode contact in both rrP3HT:PC61BM and rrP3HT:PC71BM blend BHJ solar cells and their corresponding photovoltaic performances were systematically correlated with their energy level diagram. The device with dual cathode buffer layer having ITO/PEDOT:PSS/blend polymer/BCP/LiF/Al configuration showed the best device performance with PCE, η = 4.96%, Jsc = 13.53 mA/cm(2), Voc = 0.60 V and FF= 61% for rrP3HT:PC71BM and PCE, η = 4.5% with Jsc = 13.3 mA/cm(2), Voc = 0.59 V and FF = 59% for rrP3HT:PC61BM. This drastic improvement in PCE in both the device configurations are due to the combined effects of better hole-blocking capacity of BCP and low work function provided by LiF/Al with the blend polymer. These results successfully explain the role of dual cathode buffer layers and their contribution to the PCE improvement and overall device performance with rrP3HT:PCBM based BHJ solar cell.

Combined influence of plasmonic metal nanoparticles and dual cathode buffer layers for highly efficient rrP3HT:PCBM-based bulk heterojunction solar cells

The combined influence of plasmon-induced metallic nanoparticles (NPs), which increase the photoabsorption capability, and dual cathode buffer layers for enhanced charge collection is presented, which significantly improves the efficiency of organic photovoltaic (OPV) devices. Two different types of metal NPs, viz. citrate capped gold (Au) and silver (Ag) NPs, were blended (20 v/v%) separately into a PEDOT:PSS hole transport layer. For the dual cathode buffer layer, we chose two different hole blocking layers, BPhen and BCP, with a LiF/Al cathode contact. The combined influence of both the NPs and the dual cathode buffer layers was investigated with two blend polymers, rrP3HT:PC61BM and rrP3HT:PC71BM. It was observed that for both the blend polymer systems the power conversion efficiency (PCE) increases significantly in the presence of PEDOT:PSS + AuNPs and PEDOT:PSS + AgNPs with BCP/LiF/Al as a cathode contact compared to the bare PEDOT:PSS layer. In particular, in the presence of PEDOT:PSS + AuNPs and BCP/LiF/Al, the highest PCE was observed for both the blend polymers because of the better band alignment of BCP/LiF/Al with the active layers and the superior surface plasmon resonance of the AuNPs in the visible spectrum compared to AgNPs. The device with an ITO/PEDOT:PSS + AuNPs/rrP3HT:PC61BM/BCP/LiF/Al configuration showed a PCE (η) of 4.99% with Jsc = 13.9 mA cm−2, Voc = 0.59 V and FF = 62%, whereas for ITO/PEDOT:PSS + AuNPs/rrP3HT:PC71BM/BCP/LiF/Al, the device showed a PCE (η) of 5.65% with Jsc = 16.1 mA cm−2, Voc = 0.58 V and FF = 61%. These results conclusively explain the combined influence of the dual cathode buffer layer and the plasmonic metal NPs to remarkably improve the PCE and overall device performance of rrP3HT:PCBM based BHJ solar cells.

Organic Semiconductors: A New Future of Nanodevices and Applications

Organic materials with attractive electronic and optoelectronic properties are in high demand for functional electro-optical device applications. Research on synthetic polymer and organic small molecules has gained a great deal of attention due to their potential applications in low cost, ultra-thin, and flexible products and are expected to have a revolutionary role in modern day life. Basically, organic semiconductors are imperative for a range of optoelectronic applications including organic photovoltaic devices, light-emitting diodes, organic light-emitting transistor and organic field effect transistor-driven photonics since they possess photoluminescence, electroluminescence, and nonlinear optical properties in addition to liquid crystalline, structural patterning, printing and solution casting abilities. Electronic devices based on organic materials can be fabricated by simple processing techniques and are under intense investigation in academic and industrial laboratories because of their potential for mass production of flexible and cost-effective devices models. Organic devices also possess light-weight and transparent advantages compared to silicon-based devices. Significant progress has been achieved in the development of novel materials and new device engineering in the last decade. In this regard, arylene diimide families have shown high promise as useful building blocks for the fabrication of next-generation electronic and optoelectronics devices, providing deeper insight into their transistor characteristics at the molecular scale to practical applications ranging from medicine to high end security systems. These organic compounds are being developed for improved resistance to thermal and environmental stresses, which is one of the major challenges in the field. Several other classes of compounds based on fullerene (C60) and chemically modified thiophenes are also being explored and developed for use in a plethora of devices encompassing interdisciplinary research areas. These devices, owing to their low-cost, ease of synthesis and processing, are expected to pave the way for next-generation electronics with energy-efficient security systems, sensors, photonics, and spintronic memories. In this chapter we present a brief review on the different types of organic devices, their fabrication processes, and recent applications by citing examples of oligomers and polymers.

Impact of Specifically Shaped Plasmonic Gold Nanoparticles and a Double Cathode Interfacial Layer on the Performance of Conducting Polymer-Based Photovoltaics

Specifically shaped plasmonic gold nanoparticles (AuNPs) and their combined effect with the double cathode interfacial layer for increasing the power conversion efficiency (PCE) of poly(3-hexylthiophene):(6,6)-phenyl-C61/71-butyric acid methyl ester (P3HT:PC61/71BM)-based polymer solar cells (PSCs) are methodically established. Two diverse donor–acceptor blend polymers, P3HT:PC61BM and P3HT:PC71BM, were used here along with BPhen and BCP as the buffer layers of the conventional LiF:Al cathode contact. Initially, four specifically shaped AuNPs, viz., CTAB capped gold nanorods (AuNRs), gold nanospheres (AuNSs), gold nano-ovals (AuNOs), and gold nanobranches (AuNBs) were separately synthesized and blended along with a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transporting layer to obtain four novel nanoparticle-doped hole injecting layers, and their effect on P3HT:PCBM-based polymer photovoltaic device performance was methodically analyzed. The synthesized nanoparticles were ch...

High-Performance ZnPc Thin Film-Based Photosensitive Organic Field-Effect Transistors: Influence of Multilayer Dielectric Systems and Thin Film Growth Structure

The key impact and significance of a multilayer polymer-based dielectric system on the remarkable photoresponse properties of zinc phthalocyanine (ZnPc)-based photosensitive organic field-effect transistors (PS-OFETs) have been systematically analyzed at various incident optical powers. A combination of inorganic aluminum oxide (Al2O3) and organic nonpolar poly(methyl methacrylate) (PMMA) is used as the bilayer dielectric configuration, whereas in the trilayer dielectric system, a bilayer polymer dielectric, consisting of PMMA, as the low-k dielectric polymer, on top of poly(vinyl alcohol) (PVA), the high-k polar dielectric, has been fabricated along with Al2O3 as the third layer. Before fabricating the OFETs, a systematic optimization of the nature of growth of the ZnPc molecules, deposited on PMMA-coated glass substrates at different substrate temperatures (Ts) was performed and examined by atomic-force microscopy, field-emission scanning electron microscopy, X-ray diffraction, and Raman analysis. At 90 °C, the fabricated PS-OFETs with the Al2O3/PVA/PMMA trilayer dielectric configuration showed the best p-channel behavior, with an enhanced and remarkable photoresponsivity of R ∼ 9689.39 A W–1 compared to that of the Al2O3/PMMA bilayer dielectric system (R ∼ 2679.40 A W–1) due to the polarization of the dipoles inside the polar PVA dielectric, which increases the charge transport through the channel. The charge carrier mobility of the device also improved by one order (μh ∼ 1.3 × 10–2 cm2 V–1 s–1) compared to that of the bilayer dielectric configuration (μh ∼ 3.5 × 10–3 cm2 V–1 s–1). The observed specific detectivity (D*) and NEP values of the bilayer dielectric system were 6.01 × 1013 Jones and 2.655 × 10–17 W Hz–1/2, whereas for the trilayer dielectric system, the observed D* and NEP values were 5.13 × 1014 Jones and 1.043 × 10–17 W Hz–1/2, respectively. Additionally, the operating voltage of each of the fabricated devices was also very low (−10 V) due to the influence of the inorganic high-k Al2O3 dielectric layer. The electrical stability of all of the fabricated devices was also investigated by bias stress analysis under both light and dark conditions in vacuum. To the best of our knowledge, the photoresponsivity (R) reported here with an Al2O3/PVA/PMMA trilayer dielectric configuration is the highest reported value for thin film-based PS-OFETs, at a remarkably low operating voltage of −10 V, on low-cost glass substrates without indium tin oxide or/and Si/SiO2.