Thermally activated delayed fluorescence (TADF) π-conjugated polymers are developed for solution-processed TADF-OLEDs. Benzophenone-based alternating donor-acceptor structures contribute to the small ∆EST , enabling efficient exciton-harvesting through TADF. Solution-processed OLEDs using the TADF polymers as emitters can achieve high maximum external electroluminescence efficiencies of up to 9.3%.

High-efficiency deep blue thermally activated delayed fluorescence (TADF) emitters consisting of acridan–pyrimidine donor–acceptor motifs are developed.

Organic photovoltaics (OPVs) that perform more efficiently under artificial indoor lighting conditions than they do under sunlight are attracting growing interest as they can potentially serve as ambient energy harvesters for powering low-power electronics and portable devices for the Internet of Things. Herein, solution-processed small-molecule OPVs are demonstrated to exhibit high power conversion efficiencies exceeding 16% under white LED illumination, delivering high output power densities of up to 12.4 and 65.3 μW cm–2 at 200 and 1000 lx, respectively. Increasing the open-circuit voltage (V oc) of OPVs is a critical factor for achieving higher indoor photovoltaic performance. Toward real applications, this small-molecule OPV system is adopted to fabricate six series-connected modules with an active area of ∼10 cm2 that are capable of generating a high output power surpassing 100 μW and a high V oc of over 4.2 V even under dimly lit indoor conditions of 200 lx. These results indicate that OPVs are promising as indoor electric power sources for self-sustainable electronic devices.

Optoelectronic properties of polyfluorene, a blue light-emitting organic semiconductor, are often degraded by the presence of green emission that originates mainly from oxidation of the polymer. Here, we use single-molecule electroluminescence (EL) and photoluminescence (PL) spectroscopy on polyfluorene chains confined in vertical cylinders of a phase-separated block copolymer to spectrally resolve the green band and investigate in detail the photophysical processes responsible for its appearance. In both EL and PL, a substantial fraction of polyfluorene chains shows spectrally stable green emission which is ascribed to a keto defect. In addition, in EL, we observe a new type of vibrationally resolved spectra distributed over a wide range of frequencies and showing strong spectral dynamics. Based on quantum chemical calculations, this type is proposed to originate from charge-assisted formation and stabilization of ground-state aggregates. The results are expected to have broad implications in the fields of photophysics and material design of polyfluorene materials.

A liquid crystalline block copolymer, composed of poly(ethylene oxide) (PEO) and polymethacrylate (PMA)-bearing azobenzene (Az) mesogen side chains, uniquely forms perpendicularly oriented PEO cylinders in a film on various substrates, independent of the substrate surface energy. In this paper, it is revealed that the perpendicular cylinders are formed at the air interface of the block copolymer film, as the perpendicular cylinders and liquid crystal structures were observed only in the vicinity of the air interface for a block copolymer film annealed for a short period of 5 s. On the basis of this mechanism of air-interface-induced perpendicular cylinder formation, we developed a surface covering method to prevent the perpendicular cylinder formation and instead induce parallel cylinder formation. Moreover, uniaxial cylinder films were fabricated by a combination of the surface covering and substrate rubbing methods. The surface covering layer for controlling cylinder orientation can be removed to utilize the block copolymer film for templating.