Hiroyoshi Naito

To accelerate the development of high-performance organic solar cells (OSCs), we propose a machine learning-based method for predicting key electronic transport properties—electron mobility, hole mobility, and bimolecular recombination constants—directly from current–voltage ( J – V ) characteristics. A deep neural network (DNN) was trained using simulated J – V data generated by a drift–diffusion device model. To address the inverse problem of inferring transport parameters from solar cell performance metrics ( J _SC , V _OC , fill factor), we combined the DNN model with a branch-and-bound optimization algorithm. The method was validated using both simulated and experimental J – V data. Results show that the predicted mobilities and recombination constants are in close agreement with reference values, and exhibit correct composition-dependent trends for poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C ₆₁ -butyric acid methyl ester-based OSCs. Our approach enables rapid estimation of electronic transport properties using routinely measured J – V characteristics, offering a powerful tool for guiding material design and device optimization in OSC research.

Results of a study exploring the solid‐state photoluminescence properties of two crystalline polymorphs ( O ‐form (orange prisms) and R ‐form (red prisms)) of 1,4‐bis(dicyanomethylidene)‐2,2,5,5‐tetramethyl‐3,6‐bis(4‐methoxyphenyl)‐1,2,4,5‐tetrahydropentalene ( BTP‐An ) are reported. The O ‐form was found to display more quantum‐efficient photoluminescence in a shorter‐wavelength region compared to that of the R ‐form . X‐ray crystallographic analysis suggests that a unique conformation with largely rotated 4‐methoxyphenyl (anisyl) groups and suppression of free rotation of the dicyanomethylene groups are likely responsible for the shorter wavelength and higher quantum yield for photoluminescence from the O ‐form . Also, the thermally metastable O ‐form undergoes a phase transition to generate the R ‐form upon either heating or exposure to organic solvent vapors.

Results of a study exploring the solid-state photoluminescence properties of two crystalline polymorphs (O-form (orange prism) and R-form (red prism)) of 1,4-bis(dicyanomethylidene)-2,2,5,5-tetramethyl-3,6-bis(4-methoxyphenyl)-1,2,4,5-tetrahydropentalene (BTP-An) are reported. The O-form was found to display more quantum efficient photoluminescence in a shorter-wavelength region compared to that of the R-form. X-ray crystallographic analysis suggests that a unique conformation with largely-rotated 4-methoxyphenyl (anisyl) groups and suppression of free rotation of the dicyanomethylene groups are likely responsible for the shorter wavelength and higher quantum yield for photoluminescence from the O-form. Also, the thermally metastable O-form undergoes phase transition to generate the R-form upon either heating or exposure to organic solvent vapors.

Inspired by the previous machine‐learning study that the number of hydrogen‐bonding acceptor (N_HBA) is important index for the hole mobility of organic semiconductors, seven dithienobenzothiazole (DBT) derivatives 1 a–g (N_HBA=5) were designed and synthesized by one‐step functionalization from a common precursor. X‐ray single‐crystal structural analyses confirmed that the molecular arrangements of 1b (the diethyl and ethylthienyl derivative) and 1c (the di(n‐propyl) and n‐propylthienyl derivative) in the crystal are classified into brickwork structures with multidirectional intermolecular charge‐transfer integrals, as a result of incorporation of multiple hydrogen‐bond acceptors. The solution‐processed top‐gate bottom‐contact devices of 1b and 1c had hole mobilities of 0.16 and 0.029 cm² V⁻¹s⁻¹, respectively.

Inspired by the previous machine-learning study that the number of hydrogen-bonding acceptor (NHBA) is important index for the hole mobility of organic semiconductors, we synthesized seven dithienobenzothiazole (DBT) derivatives 1a–g (NHBA = 5) by one-step functionalization from a common precursor. X-ray single-crystal structural analyses confirmed that the molecular arrangements of 1b (the diethyl and ethylthienyl derivative) and 1c (the di(n-propyl) and n-propylthienyl derivative) in the crystal are classified into brickwork structures with multidirectional intermolecular charge-transfer integrals, as a result of incorporation of multiple hydrogen-bond acceptors. The solution-processed top-gate bottom-contact devices of 1b and 1c had hole mobilities of 0.16 and 0.029 cm2 V–1s–1, respectively.

動作中の有機太陽電池の電子物性を評価するための変調分光法について述べる。変調光電流分光法と変調光起電力分光法を用いて，有機太陽電池の電子物性（電子・正孔ドリフト移動度，2分子再結合定数）を決定できる。これらの分光測定を，poly（3-hexylthiophene-2,5-diyl）（P3HT）：［6,6］-phenyl-C₆₁-butyricacidmethylester（PCBM）バルクヘテロ接合を用いた典型的な有機太陽電池で行った。電子物性に関する知見は，有機太陽電池の動作メカニズムの解明や光電変換特性の向上に重要である。また，本分光法によるさまざまな有機太陽電池の電子物性の蓄積は，材料設計にも有用である。

The propagation loss in single-mode asymmetric waveguides due to interface nanometer-roughness was studied using amplified spontaneous emission (ASE) measurements. Poly(9,9-dioctylfluorene) (F8) was used as the organic gain medium and the structure of the asymmetric waveguide was quartz glass substrate/F8/air. The propagation loss was measured at the ASE wavelength (447 nm) of amorphous F8, and the surface roughness of the substrate and F8 was measured using an atomic force microscope. The propagation losses of F8 waveguides with different F8 slab thicknesses were in good agreement with those calculated using an analytical expression for single-mode asymmetric waveguides with nanometer-roughness interfaces. The results presented herein will be useful for the design of high-performance organic lasers and organic optoelectronic integration systems.

Efficiency limiting factors of quantum dots light-emitting diodes (QLEDs) are studied by a machine learning approach using features taken from published data. Prototypical structure of Cd-based QLEDs is transparent conductive oxide (TCO)/hole transport layer (HTL)/quantum dots (QDs)/electron transport layer (ETL)/Al, fabricated by printing processes. The most important factor is the hole injection barrier from HTL to QD layer (about 1 eV in CdSe QLEDs). A mechanism of the hole injection in such QLEDs is discussed using device simulation, and the experimental results that support the mechanism are shown. In addition, other efficiency limiting factors - the electron mobility of HTL and carrier balance in QD layer - are experimentally shown.

Novel thermally-activated delayed fluorescence (TADF) materials 2Cz2SB and 2Mi2SB, possessing N-heterocycle and arylsulfonyl groups, were synthesized and their photophysical properties in solution and the solid state were characterized. 2Cz2SB and 2Mi2SB exhibit typical TADF characteristics and aggregation-induced emission or crystallization-induced emission behaviour. Specifically, they display a blueshift of photoluminescence wavelength and an increase in photoluminescence quantum yield (Φ_PL) in the aggregate and solid states, owing to suppression of thermal deactivation. The results of time-resolved IR analysis suggest that aggregate and solid state promoted suppression of geometrical changes in the excited state causes the observed increases in Φ_PL.