Organic semiconductor

About: Organic semiconductor is a research topic. Over the lifetime, 15905 publications have been published within this topic receiving 533881 citations.

Doping-induced efficiency enhancement in organic photovoltaic devices

Abstract: Performance of organic photovoltaic (OPV) devices is dramatically enhanced by doping suitable fluorescent dyes into the donor and/or acceptor layers. By doping rubrene into standard CuPc∕C60 OPV cell, a high JSC of 30.1mA∕cm2, VOC of 0.58V, and an exceptionally high power conversion efficiency of 5.58% are achieved. The performance improvement is mainly attributed to efficient light absorption by rubrene in the range of 460–530nm where two hosts have low absorbance, leading to more effective exciton formation. Their findings motivate the use of fluorescent dyes for maximizing absorption spectral coverage as well as increasing photon harvesting.

Top-Gate Organic Field-Effect Transistors with High Environmental and Operational Stability

Abstract: Over the past several years, great progress has been made in the development of organic fi eld-effect transistors (OFETs). Prototypes of electronic devices such as drivers for fl at-panel displays, [ 1 ] complementary circuits, [ 2 , 3 ] radio-frequency identifi cation tags, [ 4 ] and chemical or biological sensors [ 5 , 6 ] have already been demonstrated. While charge-carrier mobility values have improved [ 2 , 3 , 7–9 ] with comparable values for both n and p -channel transistors, long-term environmental and operational stability remain two major issues that need to be resolved before OFETs can realize their full commercial potential. Recently, much effort has been devoted to improve the stability of OFETs. [ 10–18 ] For instance, to improve the environmental stability of OFETs, air-stable organic semiconductors have been synthesized [ 10 , 11 ] or encapsulation layers have been developed. [ 12 , 13 ] On the other hand, achieving operational stability is still a major challenge faced by OFETs as well as other fi eld-effect transistor (FET) technologies, such as those based on a -Si:H, poly-Si, and metal-oxide semiconductors. The operational stability of a FET is in general related to dipolar orientation and charge trapping/de-trapping events at all its critical interfaces and in the bulk of the semiconductor and gate dielectric. [ 14–18 ] The degradation of the performance of a FET during operation is refl ected by changes of its current-voltage characteristics that result from changes of mobility ( μ ), of threshold voltage ( V th ), or variations of the capacitance density ( C in ) of the gate dielectric. The dynamics of the physical and/or chemical mechanisms producing these changes, intrinsic or extrinsic, affect the performance of a FET on different time scales. [ 14 ] The stability of a FET is determined by the total effects produced by several physical and/or chemical processes, but in general, one tends to dominate over the others. This has caused current approaches to improve the stability to focus on mitigating individual processes. [ 15–18 ] Furthermore, the stability of OFETs has been primarily evaluated in devices with a bottom-gate geometry. OFETs with a top-gate geometry are relatively rare because the choice of gate dielectric material is limited since its deposition can potentially damage the organic semiconductor layer underneath. The use of an amorphous fl uoropolymer, CYTOP,

Controlling the orientation of terraced nanoscale "ribbons" of a poly(thiophene) semiconductor.

Abstract: The large-scale manufacture of organic electronics devices becomes more feasible if the molecular orientation and morphology of the semiconductor can be controlled. Here, we report on a previously unidentified crystal shape of terraced nanoscale "ribbons" in thin films of poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (pBTTT). The ribbons form after a pBTTT film is heated above its highest temperature phase transition. In contrast to the wide terrace crystal shape previously reported, terraced ribbons have lateral widths of approximately 60 nm and lengths greater than 10 microm, with a common orientation between adjacent ribbons. Further, we report a simple and scalable flow coating process that can control the ribbon orientation without requiring special substrates or external fields. The degree of molecular orientation is small after coating but increases dramatically after the terraced ribbons are formed, indicating that an oriented minority templates the whole film structure. The large extent of orientation obtained in these polythiophene crystallites provides potential opportunities to exploit anisotropic electrical properties and to obtain detailed information about the structure of organic semiconductor thin films.

Control of the Morphology and Structural Development of Solution-Processed Functionalized Acenes for High-Performance Organic Transistors

Abstract: Solution-processable functionalized acenes have received special attention as promising organic semiconductors in recent years because of their superior intermolecular interactions and solution-processability, and provide useful benchmarks for organic field-effect transistors (OFETs). Charge-carrier transport in organic semiconductor thin films is governed by their morphologies and molecular orientation, so self-assembly of these functionalized acenes during solution processing is an important challenge. This article discusses the charge-carrier transport characteristics of solution- processed functionalized acene transistors and, in particular, focuses on the fine control of the films' morphologies and structural evolution during film-deposition processes such as inkjet printing and post-deposition annealing. We discuss strategies for controlling morphologies and crystalline microstructure of soluble acenes with a view to fabricating high-performance OFETs.

Effects of grain boundaries, field-dependent mobility, and interface trap States on the electrical Characteristics of pentacene TFT

Abstract: We have fabricated pentacene-based thin film transistors and analyzed their electrical properties with the help of two-dimensional drift-diffusion simulations which favorably compare with the experimental results. We have set up a model considering the polycrystalline nature of pentacene and the presence of grains and grain boundaries. We show how this model can be applied to different devices with different grain sizes and we analyze the relationship between mobility, grain size and applied gate voltage. On the basis of the simulation results, we can introduce an effective carrier mobility, which accounts for grain-related effects. The comparison between experimental results and simulations allows us to clearly understand the differences in the mobility derived by the analysis of current-voltage curve (as done experimentally by using standard MOSFET theory) and the intrinsic mobility of the organic layer. The effect of the pentacene/oxide interface traps and fixed surface charges has also been considered. The dependence of the threshold voltage on the density and energy level of the trap states has been outlined.