Organic semiconductor

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

Correlation of hole mobility, exciton diffusion length, and solar cell characteristics in phthalocyanine/fullerene organic solar cells

Abstract: The authors investigated heterojunction organic solar cells composed of different metal phthalocyanines (MPcs, M=Fe, Co, Ni, Cu, and H2)/fullerene (C60) and compared the solar cell characteristics with the field-effect hole mobilities (μh) and exciton diffusion length (Lex) of the different MPcs. They observed that the short circuit current (JSC) is linearly dependent on the μh of the MPcs, except for ZnPc. They also estimated the Lex of the MPcs by creating a line of best fit using the action spectra of the external quantum efficiency in the solar cells and found that JSC is closely correlated with the Lex of the MPcs.

Interchain effects in the ultrafast photophysics of a semiconducting polymer: THz time-domain spectroscopy of thin films and isolated chains in solution

Abstract: We compare the generation and decay dynamics of charges and excitons in a model polymer semiconductor (MEH-PPV) in solution and drop-cast thin films, by recording the sub-ps transient complex conductivity using THz time-domain spectroscopy. The results show that the quantum efficiency of charge generation is two orders of magnitude smaller in solution (~10–5) than in the solid film (~10–3). The proximity of neighboring chains in the films apparently facilitates (hot) exciton dissociation, presumably by allowing the electron and hole to separate on different polymer strands. For both samples, photoexcitation leads to the predominant formation of bound charge pairs (excitons) that can be detected through their polarizability. Surprisingly, the polarizability per absorbed photon is a factor of 3 larger in solution than in the film, suggesting that interchain interactions in the film do not result in a substantial delocalization of the exciton wave function.

Photoswitches and phototransistors from organic single-crystalline sub-micro/nanometer ribbons

Abstract: Photoelectronic devices of organic semiconductors are of great interest recently because organic semiconductors have many fundamental advantages over their inorganic counterparts. For example, their low cost is ideal for large-area applications and their mechanical flexibility makes them naturally compatible with plastic substrates for lightweight and foldable products. The most attractive prospect, however, is their incorporation of functionality by molecular design. Phototransistors have much higher sensitivity and lower noise than photodiodes and use these advantages to combine light detection and signal magnification properties that realize greater functionality in a single device. This is an important aspect of optoelectronic integration. Since the first concept of a phototransistor was proposed by William Shockley in 1951, inorganic phototransistors have been quickly developed and used in a variety of applications. However, few reports in the literature have addressed phototransistors made of organic semiconductors, especially organic single crystals. Organic single crystals have important merits in the study of intrinsic properties and for the fabrication of high-quality devices and circuits. Here, we used an organic semiconductor, copper hexadecafluorophthalocyanine (F16CuPc), as the candidate to introduce single-crystalline photoswitches and phototransistors of organic semiconductors. F16CuPc was selected not only because of its remarkable air-stable, n-type properties but also because of its high thermal and chemical stability. Bao et al. first paid attention to this compound in 1998. Recently, Dosch and Barrena and co-workers carefully investigated its structure and self-organization properties on a solid surface. In addition, we synthesized single-crystalline sub-micro/nanoribbons of the compound by a physical vapor transport technique and studied its field-effect performance; we demonstrated its high field-effect mobility and on/ off ratio in transistors based on an individual ribbon. However, the optical properties of this air-stable, n-type material, are still unclear. In this Communication, we study these properties by using devices made of single-crystalline sub-micro/ nanometer ribbons of F16CuPc. Single-crystalline sub-micro/nanometer ribbons of F16CuPc were synthesized and transferred or in-situ patterned onto Si/ SiO2 (300 nm) substrates, as previously described. [6,7] Devices based on an individual sub-micro/nanometer ribbon were fabricated by the “multiple-times gold-wire mask moving” technique based on the asymmetrical drain/source electrode (Au/Ag) configuration shown in Figure 1—because such a configuration was beneficial for injection, transport, and collection. The ribbon thickness in the devices was measured carefully by atomic force microscopy. C O M M U N IC A TI O N

An Effective Friedel−Crafts Postfunctionalization of Poly(N-vinylcarbazole) to Tune Carrier Transportation of Supramolecular Organic Semiconductors Based on π-Stacked Polymers for Nonvolatile Flash Memory Cell

Abstract: Poly(N-vinylcarbazole) (PVK) and its derivatives are π-stacked polymers of the most important supramolecular organic semiconductors (SOSs), in which semiconducting features are originated from intra-supramolecular interactions. An effective Friedel−Crafts method has been developed to postfunctionalize PVK to a PVK−PF SOS and to tune the fundamental electronic structures and transporting properties of the resulting SOS. Stable nonvolatile flash memory effect from the SOS has been demonstrated in an ITO/PVK−PF/metal sandwich device. The device exhibited an ON/OFF current ratio up to 104, and writing/erasing voltages around +2.2/−2.0 V, respectively. The unique electrical bistability can be attributed to the ordering alignment effect induced by electric field and the hindrance effect arisen from bulky moieties. Thus, PVK-containing complicated 9,9-diarylfluorenes (CDAFs) are promising materials for information storage applications.

The Structure and Dynamics of Molecular Excitons

Abstract: The photophysical behavior of organic semiconductors is governed by their excitonic states. In this review, I classify the three different exciton types (Frenkel singlet, Frenkel triplet, and charge transfer) typically encountered in organic semiconductors. Experimental challenges that arise in the study of solid-state organic systems are discussed. The steady-state spectroscopy of intermolecular delocalized Frenkel excitons is described, using crystalline tetracene as an example. I consider the problem of a localized exciton diffusing in a disordered matrix in detail, and experimental results on conjugated polymers and model systems suggest that energetic disorder leads to subdiffusive motion. Multiexciton processes such as singlet fission and triplet fusion are described, emphasizing the role of spin state coherence and magnetic fields in studying singlet ↔ triplet pair interconversion. Singlet fission provides an example of how all three types of excitons (triplet, singlet, and charge transfer) may interact to produce useful phenomena for applications such as solar energy conversion.