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Ultraflexible optical devices have been used extensively in next-generation wearable electronics owing to their excellent conformability to human skins. Long-term health monitoring also requires the integration of ultraflexible optical devices with an energy-harvesting power source; to make devices self-powered. However, system-level integration of ultraflexible optical sensors with power sources is challenging because of insufficient air operational stability of ultraflexible polymer light-emitting diodes. Here we develop an ultraflexible self-powered organic optical system for photoplethysmogram monitoring by combining air-operation-stable polymer light-emitting diodes, organic solar cells, and organic photodetectors. Adopting an inverted structure and a doped polyethylenimine ethoxylated layer, ultraflexible polymer light-emitting diodes retain 70% of the initial luminance even after 11.3 h of operation under air. Also, integrated optical sensors exhibit a high linearity with the light intensity exponent of 0.98 by polymer light-emitting diode. Such self-powered, ultraflexible photoplethysmogram sensors perform monitoring of blood pulse signals as 77 beats per minute. Flexible electronic devices remain an attractive technology for optical sensor applications that require long-term health monitoring and conformability on human skin. Here, the authors report an ultrathin self-powered integrated organic optical system for plethysmogram monitoring.

Textile-compatible photovoltaics play a crucial role as a continuous source of energy in wearable devices. In contrast to other types of energy harvester, they can harvest sufficient electricity (on the order of milliwatts) for wearable devices by utilizing the cloth itself as the platform for photovoltaics. Three features are important for textile-compatible photovoltaics, namely environmental stability, sufficient energy efficiency and mechanical robustness. However, achieving these simultaneously remains difficult because of the low gas barrier properties of ultrathin superstrates and substrates. Here, we report on ultraflexible organic photovoltaics coated on both sides with elastomer that simultaneously realize stretchability and stability in water whilst maintaining a high efficiency of 7.9%. The efficiency of double-side-coated devices decreases only by 5.4% after immersion in water for 120 min. Furthermore, the efficiency of the devices remains at 80% of the initial value even after 52% mechanical compression for 20 cycles with 100 min of water exposure. Organic solar cells can be thin, bendable and strechable. Now, Jinno et al. develop flexible organic photovoltaic devices that can also be washed in water and detergent, opening future integration routes into everyday objects such as fabric.

In this work, we investigated the feasibility of using strongly electron-deficient naphthobispyrazine bisimide (NPI) as a building unit for n-type semiconducting polymers used in organic photovoltaics. We synthesized new n-type semiconducting polymers based on NPI, in which thienothiophene and thiophene were used as counits. The polymers exhibited deep lowest unoccupied molecular orbital energy levels of ~−3.7 eV and narrow optical bandgaps of less than 1.5 eV, which originated from the high electron deficiency of NPI. We found that decreasing the counit length improved the solubilities and reduced the crystallinities of the NPI-based polymers. When blended with the benchmark p-type polymer PTB7-Th, the NPI-based polymers afforded power conversion efficiencies of up to 1.6% and exhibited clear photoresponses at the absorption band of NPI-based polymers. This study shows that NPI-based polymers have good potential as n-type materials for use in organic photovoltaic cells.The feasibility of using strongly electron-deficient naphthobispyrazine bisimide (NPI) as a building unit for n-type semiconducting polymers used in all-polymer organic photovoltaics (OPV) cells was investigated. The NPI-based polymers had sufficiently deep LUMO energy levels of ~−3.7 eV and narrow bandgaps of less than 1.5 eV, which matched well energetically with p-type polymers exhibiting wide optical bandgaps. The NPI-based polymers exhibited a clear photoresponse in all-polymer OPV cells blended with PTB7-Th as a benchmark p-type polymer and showed power conversion efficiencies of up to 1.6%.

Ternary polymer solar cells based on a thiazolothiazole-based polymer donor (PTzBT) and a fullerene acceptor (PC 61 BM) have attracted attention because they show high efficiency and stability by addition of a non-fullerene acceptor (ITIC). However, the performance improvement mechanism is not completely elucidated. Here, we show the stability improvement mechanism due to less charge accumulation in the PTzBT cells with ITIC using operando electron spin resonance from a microscopic viewpoint. We observed two correlations between device performance and number of spins ( N spin ) under solar irradiation. One correlation is the decrease in short-circuit current and the N spin increase in electrons on PC 61 BM and holes in PTzBT, where the ITIC addition causes the less these N spin . The other correlation is the increase in open-circuit voltage and the N spin decrease in holes in ZnO. These findings explain the stability improvement mechanism, showing the correlation between less charge accumulation and higher stability, which is valuable for the development of further efficient and stable polymer solar cells.

A critical issue in polymer-based solar cells (PSCs) is to improve the power conversion efficiency (PCE) as well as the stability. Here, we describe the development of new semiconducting polymers consisting of thiophene, thiazolothiazole and naphthobisthiadiazole in the polymer backbone. The polymers had good solubility and thus solution-processability, appropriate electronic structure with narrow band gaps of ~1.57 eV and low-lying HOMO energy levels of ~−5.40 eV and highly ordered structure with the favorable face-on backbone orientation. Solar cells based on the polymers and PC 71 BM exhibited quite high PCEs of up to 9%. More interestingly, the cells also demonstrated excellent stability as they showed negligible degradation of PCE when stored at 85˚C for 500 hours in the dark under nitrogen atmosphere. These results indicate that the newly developed polymers are promising materials for PSCs in the practical use.

A direct reductive homo-coupling of alkyl tosylates has been developed by employing a combination of nickel and nucleophilic cobalt catalysts. A single-electron-transfer-type oxidative addition is a pivotal process in the well-established nickel-catalyzed coupling of alkyl halides. However, the method cannot be applied to the homo-coupling of ubiquitous alkyl tosylates due to the high-lying σ*(C–O) orbital of the tosylates. This paper describes a Ni/Co-catalyzed protocol for the activation of alkyl tosylates on the construction of alkyl dimers under mild conditions.

To investigate the effect of the branching position of the alkyl groups on the side chain of semiconducting polymers, we synthesized two series of semiconducting polymers based on thienothiophene-2,5-dione ( PTTD4T s) and quinacridone ( PQA2T s). 2-Decyltetradecyl, 3-decylpentadecyl, 4-decylhexadecyl, and 5-decylheptadecyl groups were used, and the branching position was systematically varied from the second carbon from the backbone to the fifth carbon. These branched side chains are introduced into the thiophene ring for PTTD4T s and the quinacridone unit for PQA2T s. The polymer thin films exhibited small but clear differences in their optical absorption spectra, suggesting that the intermolecular interaction in the solid state varied based on the branching position. The grazing incident X-ray diffraction study revealed that the π–π stacking d -spacing of both polymers decreased when the branching position was moved away from the backbones, indicating that the intermolecular interaction was enhanced. Therefore, regardless of the core where the alkyl groups were introduced, the branching position effectively improved the ordering structure of the polymers, which was most likely due to suppressed steric hindrance. Although PTTD4T s did not exhibit a clear correlation between the branching position and charge carrier mobility, the mobility of PQA2T s gradually increased as the branching position moved away from the backbone. To investigate the effect of the branching position of the alkyl side chain of semiconducting polymers, we synthesized two series of semiconducting polymers based on thienothiophene-2,5-dione ( PTTD4T s) and quinacridone ( PQA2T s). The polymer thin films exhibited small but clear differences in their optical absorption spectra and X-ray diffraction patterns, suggesting that the intermolecular interaction in the solid state varied as a function of the branching position. Although PTTD4T s did not exhibit a clear correlation between the branching position and charge carrier mobility, the mobility of PQA2T s gradually increased as the branching position moved away from the backbone.

Evaporable indano[60]fullerene ketone (FIDO) was converted to indano[60]fullerene thioketone (FIDS) in high yield by using Lawesson's reagent. Three compounds with different substituents in para position were successfully converted to the corresponding thioketones, showing that the reaction tolerates compounds with electron-donating and electron-withdrawing substituents. Computational studies with density functional theory revealed the unique vibrations of the thioketone group in FIDS. The molecular structure of FIDS was confirmed by single-crystal X-ray analysis. Bulk heterojunction organic solar cells using three evaporable fullerene derivatives (FIDO, FIDS, C 60 ) as electron-acceptors were compared, and the open-circuit voltage with FIDS was 0.16 V higher than that with C 60 .

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.

The cobalt/chromium-catalyzed three-component coupling of aryl iodides, allenes, and aldehydes has been developed to afford multi-substituted homoallylic alcohols in a diastereoselective manner. Control experiments for understanding the reaction mechanism reveal that the cobalt catalyst is involved in the oxidative addition and carbometalation steps in the reaction, whereas the chromium salt generates highly nucleophilic allylchromium intermediates from allylcobalt species, without the loss of stereochemical information, to allow the addition to aldehydes.