Yasuhiko Shirota

Bio: Yasuhiko Shirota is an academic researcher from Fukui University of Technology. The author has contributed to research in topics: Amorphous solid & Polymerization. The author has an hindex of 42, co-authored 298 publications receiving 8298 citations. Previous affiliations of Yasuhiko Shirota include Osaka University.

Organic materials for electronic and optoelectronic devices

Abstract: This article concentrates on our recent results on several classes of photo- and electro-active organic materials that permit thin film formation and discusses their synthesis, properties, functions and potential applications for electronic and optoelectronic devices. The materials studied include amorphous molecular materials, titanyl phthalocyanine, oligothiophenes with well-defined structures, and non-conjugated polymers containing pendant oligothiophenes or other π-electron systems. The thin films of these materials find potential applications for use in organic electroluminescent, photovoltaic, electrochromic, and other devices.

A Novel Class of Emitting Amorphous Molecular Materials with Bipolar Character for Electroluminescence

Abstract: A novel class of color-tunable emitting amorphous molecular materials with desired bipolar character, 4-dimesitylboryl-N,N-bis(9,9-dimethylfluoren-2-yl)aniline (FlAMB-0T), 2-{4-[bis(9,9-dimethylfluoren-2-yl)amino]phenyl}-5-(dimesitylboryl)thiophene (FlAMB-1T), 2-{4-[bis(9,9-dimethylfluoren-2-yl)amino]phenyl}-2‘-dimesitylboryl-5,5‘-bithiophene (FlAMB-2T), and 5-{4-[bis(9,9-dimethylfluoren-2-yl)amino]phenyl}-5‘ ‘-dimesitylboryl-2,2‘:5‘,2‘ ‘-terthiophene (FlAMB-3T), have been designed and synthesized. This novel class of compounds is characterized by reversible anodic oxidation and cathodic reduction, intense fluorescence emission, and ready formation of stable amorphous glasses with high glass-transition temperatures above 120 °C. They function as excellent emitting materials for organic electroluminescent (EL) devices, emitting multicolor light including white. They also serve as good host materials for emissive dopants in organic EL devices, permitting color tuning and leading to higher performance.

Conjugated polymer-based organic solar cells

Abstract: The need to develop inexpensive renewable energy sources stimulates scientific research for efficient, low-cost photovoltaic devices.1 The organic, polymer-based photovoltaic elements have introduced at least the potential of obtaining cheap and easy methods to produce energy from light.2 The possibility of chemically manipulating the material properties of polymers (plastics) combined with a variety of easy and cheap processing techniques has made polymer-based materials present in almost every aspect of modern society.3 Organic semiconductors have several advantages: (a) lowcost synthesis, and (b) easy manufacture of thin film devices by vacuum evaporation/sublimation or solution cast or printing technologies. Furthermore, organic semiconductor thin films may show high absorption coefficients4 exceeding 105 cm-1, which makes them good chromophores for optoelectronic applications. The electronic band gap of organic semiconductors can be engineered by chemical synthesis for simple color changing of light emitting diodes (LEDs).5 Charge carrier mobilities as high as 10 cm2/V‚s6 made them competitive with amorphous silicon.7 This review is organized as follows. In the first part, we will give a general introduction to the materials, production techniques, working principles, critical parameters, and stability of the organic solar cells. In the second part, we will focus on conjugated polymer/fullerene bulk heterojunction solar cells, mainly on polyphenylenevinylene (PPV) derivatives/(1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61) (PCBM) fullerene derivatives and poly(3-hexylthiophene) (P3HT)/PCBM systems. In the third part, we will discuss the alternative approaches such as polymer/polymer solar cells and organic/inorganic hybrid solar cells. In the fourth part, we will suggest possible routes for further improvements and finish with some conclusions. The different papers mentioned in the text have been chosen for didactical purposes and cannot reflect the chronology of the research field nor have a claim of completeness. The further interested reader is referred to the vast amount of quality papers published in this field during the past decade.

Small molecular weight organic thin-film photodetectors and solar cells

Abstract: In this review, we discuss the physics underlying the operation of single and multiple heterojunction, vacuum-deposited organic solar cells based on small molecular weight thin films. For single heterojunction cells, we find that the need for direct contact between the deposited electrode and the active organics leads to quenching of excitons. An improved device architecture, the double heterojunction, is shown to confine excitons within the active layers, allowing substantially higher internal efficiencies to be achieved. A full optical and electrical analysis of the double heterostructure architecture leads to optimal cell design as a function of the optical properties and exciton diffusion lengths of the photoactive materials. Combining the double heterostructure with novel light trapping schemes, devices with external efficiencies approaching their internal efficiency are obtained. When applied to an organic photovoltaic cell with a power conversion efficiency of 1.0%±0.1% under 1 sun AM1.5 illuminati...

Organic solar cells: An overview

Abstract: Organic solar cell research has developed during the past 30 years, but especially in the last decade it has attracted scientific and economic interest triggered by a rapid increase in power conversion efficiencies. This was achieved by the introduction of new materials, improved materials engineering, and more sophisticated device structures. Today, solar power conversion efficiencies in excess of 3% have been accomplished with several device concepts. Though efficiencies of these thin-film organicdevices have not yet reached those of their inorganic counterparts (η ≈ 10–20%); the perspective of cheap production (employing, e.g., roll-to-roll processes) drives the development of organic photovoltaic devices further in a dynamic way. The two competitive production techniques used today are either wet solution processing or dry thermal evaporation of the organic constituents. The field of organic solar cells profited well from the development of light-emitting diodes based on similar technologies, which have entered the market recently. We review here the current status of the field of organic solar cells and discuss different production technologies as well as study the important parameters to improve their performance.