π-Conjugated polymers and molecules enabling small photon energy loss simultaneously with high efficiency in organic photovoltaics

Organic photovoltaics (OPVs) are a topic of significant research interest in the field of renewable energy as well as organic electronics. The crucial issue in OPVs is the improvement of the power conversion efficiency (PCE). In addressing this issue, one of the most important factors is the photon energy loss (Eloss), which is defined as the difference between the bandgap of the materials and the energy corresponding to the open-circuit voltage. Typically, the Eloss for OPVs is considerably larger than that for inorganic and perovskite photovoltaics, which has prevented OPVs from generating larger photovoltages. In parallel, reducing the Eloss for OPVs causes a loss of driving-force energy for charge generation, which is detrimental to the generation of photocurrent. Thus, OPVs have been facing a trade-off between photocurrent and photovoltage. However, a number of recently developed π-conjugated materials for use as p-type and n-type organic semiconductors have been shown to enable small Eloss values that are close to those for inorganic systems, simultaneously with efficient charge generation. Here, we summarize recent progress in π-conjugated polymers and molecules that enable small Eloss and high PCE at the same time. We hope that this review will be of help to chemists and materials scientists who are involved in the design of materials and blends with an eye toward highly efficient OPVs

Interleukin-8 Producing Malignant Fibrous Histiocytoma with Prolonged Fever

We present a case of malignant fibrous histiocytoma accompanied by prolonged spiking fevers, which disappeared after tumor resection. Sarcoma with fever as a primary symptom is rare. Furthermore, in this case, fever was closely related to the clinical course of the tumor. In order to detect possible production of febriferous substance(s), we used blood and tumor tissue samples to investigate nine candidate cytokines possibly responsible for the fever. Expression of IL-8 mRNA was detected in preoperative peripheral blood mononuclear cells by RT-PCR. Expressions of IL-6, IL-8, IFN-γ and TNF-α mRNAs were also detected in tumor tissue, while IL-1α, IL-1β, IL-2, IL-4 and COX-2 mRNAs were not. We suspected IL-8 to be a causative factor, and examined its localization by immunohistochemical staining, paraffin sections of tumor tissue stained positive for IL-8. Since infiltrating mononuclear cells were positive for IL-8, this may explain the tumor-associated fever. This case involves intratumoral production of IL-8 as a causative factor, and IL-6, IL-8, IFN-γ and TNF-α cytokine production might have resulted from stimulation with a substance(s) derived from tumor tissue, since the fever disappeared postoperatively. To date the patient is alive and in good health for 7 years and 2 months since the surgery

Photon energy loss in ternary polymer solar cells based on nonfullerene acceptor as a third component

Understanding photon energy loss caused by the charge recombination in ternary blend polymer solar cells based on nonfullerene acceptors (NFAs) is crucial for achieving further improvements in their device performance. In such a ternary system, however, the two types of donor/acceptor interface coexist, making it more difficult to analyze the photon energy loss. Here, we have focused on the origin of the voltage loss behind a high open-circuit voltage (Voc) in ternary blend devices based on one donor polymer (poly(2, 5-bis(3-(2-butyloctyl)thiophen-2-yl)-thiazolo[5, 4-]thiazole) [PTzBT]) and two acceptors, including a fullerene derivative ([6, 6]-phenyl-C₆₁-butyric acid methyl ester [PCBM]) and an NFA ((2, 2′-((2Z, 2′Z)-(((4, 4, 9, 9-tetrakis(4-hexylphenyl)-4, 9-dihydro-sindaceno[1, 2-:5, 6-b′]dithiophene-2, 7-diyl)bis(4-((2-ethylhexyl)oxy)thiophene-5, 2-diyl))bis(methanylylidene))bis(5, 6-difluoro-3-oxo-2, 3-dihydro-1H-indene-2, 1-diylidene))dimalononitrile) [IEICO-4F]), which exhibit VOC similar to that of fullerene-based PTzBT/PCBM binary devices. From the temperature-dependent VOC, we found that the effective interfacial bandgap is the same between them: the PTzBT/PCBM/IEICO-4F ternary blend device is the same as the PTzBT/PCBM fullerene-based binary device rather than the PTzBT/IEICO-4F nonfullerene-based binary device. This means that the recombination center of the ternary blend device is still the interface of PTzBT/PCBM regardless of the incorporation of a small amount of NFA. On the basis of detailed balance theory, we found that the radiative and nonradiative recombination voltage losses for PTzBT/PCBM/IEICO-4F ternary devices significantly reduced compared to those of fullerene-based PTzBT/PCBM binary counterparts. This is ascribed to the disappearance of charge transfer absorption due to overlap with the absorption of NFA and the reduction of energetic disorder due to the incorporation of NFA. Through this study, the role of NFAs in voltage loss is once again emphasized, and a ternary system capable of achieving high Voc resulting from significantly reduced voltage loss in ternary blend solar cells is proposed. Therefore, we believe that this research proposes the guidelines that can further enhance the power conversion efficiency of polymer solar cells

Significantly Sensitized Ternary Blend Polymer Solar Cells with a Very Small Content of the Narrow-Band Gap Third Component That Utilizes Optical Interference

光干渉効果を利用し、低コストで有機薄膜太陽電池を飛躍的に高効率化することに成功. 京都大学プレスリリース. 2020-12-02.Increasing photon harvest is an essential issue in improving the efficiency of organic photovoltaics. Here, we study ternary blend polymer solar cells that are composed of a thiazolothiazole-based crystalline semiconducting polymer and a fullerene derivative as the host binary system and a very small content of a series of narrow-band gap non-fullerene acceptors as the third-component sensitizer that is selectively located at the interface between the host donor and acceptor. Surprisingly, the cells give an external quantum efficiency in the sensitizer absorption range that is as high as that in the polymer absorption range despite the fact that the optimal sensitizer content is only 6 wt %, which is far smaller than the host polymer contents. This leads to significantly improved photocurrents and, in turn, high power conversion efficiencies relative to the binary blend cell. Such pronounced sensitization is found to originate in the markedly amplified sensitizer absorption owing to the optical interference effect of more than 300 nm-thick photoactive layers. In parallel, the ternary blend system realizes markedly reduced photon energy loss, which is also important for the power conversion efficiency improvement, and high thermal stability. With such excellent features, we believe that the sensitized ternary blend cells have exceptional possibilities and that exploring more well-matched material combinations would improve the performance further

A highly crystalline face-on -conjugated polymer based on alkoxythiophene-flanked benzobisthiazole for organic photovoltaics

The use of noncovalent intramolecular interactions constitutes a powerful design strategy for preparing π-conjugated polymers featuring high backbone coplanarities and thereby high crystallinities. Herein, we report the design and synthesis of an alkoxythiophene-flanked benzobisthiazole (BBTz) as a new building unit for π-conjugated polymers, which was subsequently copolymerized to give a simple BBTz-bithiophene copolymer with alkyl and alkoxy groups (PDBTz2). Owing to the S···O noncovalent intramolecular interactions between the alkoxy oxygens and thiazole sulfurs in BBTz, PDBTz2 showed greater coplanarity and crystallinity than its alkyl counterpart, PDBTz1. Interestingly, the backbone orientation was completely altered from the edge-on orientation observed for PDBTz1 to a face-on orientation for PDBTz2, which is preferable for organic photovoltaics (OPVs). In addition, the electron-donating nature of the alkoxy group increased the HOMO energy level of PDBTz2 compared to that of PDBTz1, which enabled photoinduced hole transfer from a nonfullerene acceptor, Y6, to the polymer. As a result, the short-circuit current density of an organic photovoltaic cell based on PDBTz2 and Y6 was significantly greater than that of a cell based on PDBTz1 and Y6. This study confirmed that alkoxythiophene-flanked BBTz is a promising building unit for high-performance π-conjugated polymers

Halogen‐Free πupiupi‐Conjugated Polymers Based on Thienobenzobisthiazole for Efficient Nonfullerene Organic Solar Cells: Rational Design for Achieving High Backbone Order and High Solubility

In π-conjugated polymers, a highly ordered backbone structure and solubility are always in a trade-off relationship that must be overcome to realize highly efficient and solution-processable organic photovoltaics (OPVs). Here, it is shown that a π-conjugated polymer based on a novel thiazole-fused ring, thieno[2′, 3′:5, 6]benzo[1, 2-d:4, 3-d′]bisthiazole (TBTz) achieves both high backbone order and high solubility due to the structural feature of TBTz such as the noncovalent interlocking of the thiazole moiety, the rigid and bent-shaped structure, and the fused alkylthiophene ring. Furthermore, based on the electron-deficient nature of these thiazole-fused rings, the polymer exhibits deep HOMO energy levels, which lead to high open-circuit voltages (VOCs) in OPV cells, even without halogen substituents that are commonly introduced into high-performance polymers. As a result, when the polymer is combined with a typical nonfullerene acceptor Y6, power conversion efficiencies of reaching 16% and VOCs of more than 0.84 V are observed, both of which are among the top values reported so far for “halogen-free” polymers. This study will serve as an important reference for designing π-conjugated polymers to achieve highly efficient and solution-processable OPVs

Synchronized UCN storage for superthermal SD_2 converter

We propose to experimentally verify a principle of a substantially new type of compact source for Ultra Cold Neutrons (UCN) in support of designing a practical source dedicated to researches on fundamental particle physics in the 21^ century such as the electro-weak interaction, the new models beyond the standard model, the gravity, and so on with improved sensitivity. The novelty of this UCN source is to efficiently accumulate UCN emitted in a pulsed scheme from a surface of a superthermal converter, solid deuterium (SD_2) by using a large kick-out velocity (～5 m/s) of UCN from the SD_2 surface and a moving membrane synchronized with pulsed proton beam. This will enable us to make a much more compact UCN source with a performance higher than others ever constructed. We perform experimental verification of the proposed concept by making use of a prototype assembly consisting of the SD_2 converter, a moving membrane, a compact UCN storage vessel and a UCN detector with pulsed proton beam. As a promising pre-moderator, solid mesitylene (C_6H_3(CH_3)_3) operated at low temperatures (≦ 20 K) is examined on the suitability for a pre-moderator satisfying a time structure condition required for the present method of synchronized UCN storage. This test will be done by observing the time dependence of the intensity and the energy spectra of cold neutrons from solid mesitylene with the TOF method. For this purpose, we will observe the time dependences of energy spectra for produced cold neutrons emerging out of the mesitylene pre-moderator by a TOF method

A Thiazolothiazole-Based Semiconducting Polymer with Well-Balanced Hole and Electron Mobilities

We report the synthesis and properties of a new thiazolothiazole (TzTz)-based semiconducting polymer incorporating the dithienothienothiophenebisimide (TBI) unit, named PTzTBI. PTzTBI showed relatively deep HOMO and LUMO energy levels of −5.48 and −3.20 eV, respectively. Although PTzTBI mainly formed face-on backbone orientation unfavorable for transistors, PTzTBI functioned as an ambipolar semiconductor for the first time with TzTz-based polymers, with reasonably high and well-balanced hole (0.02 cm2 V−1 s−1) and electron (0.01 cm2 V−1 s−1) mobilities