Fumitaka Ishiwari

Lead halide perovskite solar cells have emerged as promising candidates for next-generation photovoltaics; nevertheless, fabrication of the perovskite photoactive layer remains highly intricate with film formation strongly modulated by various processing and environmental factors. Here, we report an environment-controlled, robot-assisted platform for automated thin-film fabrication designed to quantify and visualize perovskite crystallization in situ. Beyond precise control of each processing step, the system captures dynamic phenomena spanning subsecond color evolution and millisecond antisolvent droplet behavior while simultaneously recording slower environmental parameters (temperature, humidity/moisture, and concentrations of oxygen and volatile organic compounds). For optoelectronic assessment, we implemented time-resolved microwave conductivity (TRMC) measurements together with photoluminescence intensity quantification by using a complementary automated evaluation system. By combining machine-learning regression with SHAP (Shapley additive explanations) analysis, we identify the environmental parameters that most impact film properties and propose a feedback strategy to refine data and extract precise effects of process factors. A comparative study of a two-cation perovskite, (FAPbI3)0.87(MAPbBr3)0.13, and a three-cation perovskite, FA0.85MA0.10Cs0.05PbI3, further reveals markedly different sensitivities to environmental factors (FA, formamidinium; MA, methylammonium), in particular, temperature and resultant phase transition kinetics during thermal annealing. Based on the ML analysis and feedback, we tuned the antisolvent droplet velocity and obtained the maximized power conversion efficiency of 24.4%. Notably, this manual device fabrication was consistent with the results obtained by the automated system. This work establishes a practical route to stable, quantitative, and mechanistically informed investigation of solution-processed photovoltaic films.

The development of a new building block for creating solution‐processable amorphous n‐type semiconductors provides a platform of fundamental importance for advanced organic electronic materials. We have recently demonstrated that oxidative inner‑bond cleavage of readily available dibenzo[ g , p ]chrysene affords a chiral figure‑eight macrocycle that bears electron‑withdrawing carbonyl groups, namely cyclobisbiphenylenecarbonyl (CBBC). In this study, we report a highly electron‑accepting derivative of CBBC (CBBC‑TIC), in which the CBBC core is connected to four electron‑withdrawing dicyanomethylene‑3‑indanone (IC) units via thiophene spacers. The distinctive X‑shaped molecular structure of CBBC‑TIC enables the solution‐process fabrication of a homogeneous amorphous film with good electron conductivity. Perovskite solar cells that contain CBBC‑TIC as the electron‐transport layer achieved a power conversion efficiency of 20.6%, which is comparable to that obtained with the benchmark fullerene derivative [6,6]‐phenyl‐C ₆₁ ‐butyric acid methyl ester (PCBM). Furthermore, the enantiomers of CBBC‐TIC exhibited spin‐selective electron transport arising from the chirality‐induced spin‐selectivity (CISS) effect, with remarkably high enantiospecific magnetic conductance asymmetry values of up to 80% in amorphous films. These findings demonstrate that CBBC represents a versatile molecular component for the creation of advanced non‑fullerene n‐type semiconductors.

The development of a new building block for creating solution‐processable amorphous n‐type semiconductors provides a platform of fundamental importance for advanced organic electronic materials. We have recently demonstrated that oxidative inner‑bond cleavage of readily available dibenzo[ g , p ]chrysene affords a chiral figure‑eight macrocycle that bears electron‑withdrawing carbonyl groups, namely cyclobisbiphenylenecarbonyl (CBBC). In this study, we report a highly electron‑accepting derivative of CBBC (CBBC‑TIC), in which the CBBC core is connected to four electron‑withdrawing dicyanomethylene‑3‑indanone (IC) units via thiophene spacers. The distinctive X‑shaped molecular structure of CBBC‑TIC enables the solution‐process fabrication of a homogeneous amorphous film with good electron conductivity. Perovskite solar cells that contain CBBC‑TIC as the electron‐transport layer achieved a power conversion efficiency of 20.6%, which is comparable to that obtained with the benchmark fullerene derivative [6,6]‐phenyl‐C ₆₁ ‐butyric acid methyl ester (PCBM). Furthermore, the enantiomers of CBBC‐TIC exhibited spin‐selective electron transport arising from the chirality‐induced spin‐selectivity (CISS) effect, with remarkably high enantiospecific magnetic conductance asymmetry values of up to 80% in amorphous films. These findings demonstrate that CBBC represents a versatile molecular component for the creation of advanced non‑fullerene n‐type semiconductors.

Chirality‐induced spin selectivity (CISS) is emerging as a key element for spin‐dependent functions in organic electronics. We previously developed a chiral bifacial indacenodithiophene (IDT) backbone that shows strong CISS in both π ‐conjugated polymers and non‐fullerene acceptors (NFAs). Building on this platform, here we report triarylamine‐functionalized, chiral bifacial IDT‐based hole‐transport materials (HTMs). Spin‐coated films of ( R , R )‐ 1 and ( S , S )‐ 1 exhibit pronounced CISS with spin polarization (SP) ≈ 60%. Across our chiral‐bifacial IDT series, π ‐conjugated polymers, NFAs, and these HTMs, we observe a consistent chirality‐spin polarity correspondence: ( S , S ) chirality yields negative SP, whereas ( R , R ) yields positive SP, representing a platform‐level demonstration across three material classes. In perovskite solar cells, these HTMs also act as effective surface passivators; devices passivated with homochiral ( R , R )‐ 1 gave higher efficiencies than meso ‐ or racemic counterparts. Space–charge‐limited current measurements likewise indicate approximately threefold higher hole mobility for the homochiral film relative to the racemate. While a direct causal connection to the CISS effect remains to be demonstrated, these observations are consistent with a CISS‐assisted, efficient spin‐selective transport mechanism. Taken together, this work establishes a chirality‐spin polarity correspondence and demonstrates effective perovskite passivation, with higher hole mobility correlating with homochirality, highlighting new opportunities for homochiral materials in device science.

The development of structural concepts in polymers has repeatedly enabled advances in molecular organization and emergent functions. Here we introduce “bifacial ladder polymers” —rigid double-stranded backbones bearing two deliberately differentiated molecular faces— realized through a chirality-assisted synthetic strategy. To implement this architecture, we designed a C ₂ -chiral 2,8-dibromoindenofluorene monomer bearing two different substituents with syn stereochemistry across the sp ³ -carbon pair, such that only one ladderization geometry is accessible. Polymerization of the enantiopure monomers with a diboronate comonomer under Suzuki-Miyaura conditions affords precursor polymers, which undergo regioselective ladderization to yield well-defined bifacial ladder polymers with fully preserved facial differentiation. The homochiral bifacial ladder polymers display emergent chiroptical behaviour in the solid state: thin films form one-handed supramolecular helices with circular dichroism intensities over 100-fold stronger than those of their monomeric or non-ladder analogues. Strikingly, these films also exhibit robust chirality-induced spin selectivity, with spin-polarization values exceeding ±90% and opposite signs for the two enantiomers, far surpassing their precursor polymers. These results demonstrate that bifacial ladder polymers provide a versatile platform for emergent self-assemblies and functions in organic polymeric materials.

Color‐sensitive photodetectors are at the forefront of next‐generation light‐ and image‐sensing research. In this context, a photovoltaic device employing SbSI:Sb ₂ S ₃ and TiO ₂ as the visible light absorber and electron transport material, respectively, exhibits a unique wavelength‐dependent photovoltage effect and its reversible output in response to changing humidity levels. However, the specific functions of the individual layers of the device and their interaction with water remain largely unknown. In this study, we perform in situ X‐ray absorption spectroscopy (XAS) of thin films under humidity‐controlled conditions to reveal the interaction between water and the photovoltaic layers. The oxygen K‐edge XAS data reveal the adsorption of water molecules onto TiO ₂ . Ultraviolet (UV) irradiation of TiO ₂ can trigger photochemical reactions of the adsorbed water at the interface, which is considered to contribute to changes in the photovoltage. Based on this finding, we introduce hydrophilic layers between TiO ₂ and SbSI:Sb ₂ S ₃ to promote the accumulation of water in the devices, which successfully enhance both the wavelength sensitivity and response speed. Finally, we demonstrate color recognition with various irradiation intensities, thereby broadening the scope and applications of unique wavelength‐responsive single‐cell photovoltaics.

Luminescent radicals are an emerging class of materials for organic electronics, bioimaging, and quantum applications. Circularly polarized luminescence (CPL) from luminescent radicals with propeller‐type chirality remains challenging because it is difficult to simultaneously achieve high photoluminescence quantum yield (PLQY), high stability, and high racemization barriers. A series of brominated chiral luminescent radicals, CzTTBrM, 2CzTTBrM, and 3CzTTBrM, was obtained by attaching carbazole donors to TTBrM. The donor‐acceptor‐type design induces red to near‐infrared (NIR) emission via charge transfer (CT) excited states with remarkably high PLQY (up to 76%) and high photostability. The new radicals possess high racemization barriers (Δ G ^‡ (353K) = 27.9–29.1 kcal/mol), allowing the isolation of enantiopure compounds at room temperature. The enantiopure radicals exhibit CPL with broad emission across the red to NIR range (650–800 nm) and display B _CPL values (0.76–1.1), nearly one order of magnitude higher than that of TTBrM (B _CPL = 0.16). Moreover, doping these radicals into polystyrene microspheres produces whispering gallery mode (WGM) resonances, marking the first observation of WGM emission from luminescent radicals. This strategy establishes a versatile platform for integrating spin, chirality, and luminescence, offering new opportunities for applications in electroluminescence, bioimaging, and quantum photonics.

Luminescent radicals are an emerging class of materials for organic electronics, bioimaging, and quantum applications. Circularly polarized luminescence (CPL) from luminescent radicals with propeller‐type chirality remains challenging because it is difficult to simultaneously achieve high photoluminescence quantum yield (PLQY), high stability, and high racemization barriers. A series of brominated chiral luminescent radicals, CzTTBrM, 2CzTTBrM, and 3CzTTBrM, was obtained by attaching carbazole donors to TTBrM. The donor‐acceptor‐type design induces red to near‐infrared (NIR) emission via charge transfer (CT) excited states with remarkably high PLQY (up to 76%) and high photostability. The new radicals possess high racemization barriers (Δ G ^‡ (353K) = 27.9–29.1 kcal/mol), allowing the isolation of enantiopure compounds at room temperature. The enantiopure radicals exhibit CPL with broad emission across the red to NIR range (650–800 nm) and display B _CPL values (0.76–1.1), nearly one order of magnitude higher than that of TTBrM (B _CPL = 0.16). Moreover, doping these radicals into polystyrene microspheres produces whispering gallery mode (WGM) resonances, marking the first observation of WGM emission from luminescent radicals. This strategy establishes a versatile platform for integrating spin, chirality, and luminescence, offering new opportunities for applications in electroluminescence, bioimaging, and quantum photonics.

Mixed-anion compounds incorporating multiple anionic species within a single crystal lattice can exhibit novel structural and functional properties and so have recently attracted much attention. These materials offer unique coordination environments that can lead to emergent behaviors relevant to various applications. Coordination polymers (CPs) comprising metal centers bridged by molecular anionic linkers represent a subclass of mixed-anion compounds and are of interest. In particular, CPs featuring metal-sulfur (-M-S-)_n frameworks are promising candidates for optoelectronic and catalytic applications due to the unique light absorption characteristics of these materials. The present study synthesized and characterized a new visible-light-responsive Pb(II)-based CP, termed STF-1 (Science Tokyo Framework 1; [Pb(mptt)₂]_n, mptt = 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thiolate). This CP exhibits an optical bandgap of 2.50 ± 0.2 eV and so is responsive to visible light. STF-1 also demonstrates charge carrier transport through the mptt ligand moiety, as supported by first-principles density functional theory calculations. Photocatalytic experiments under visible light irradiation established that STF-1 selectively reduces CO₂ to formate with high selectivity and minimal hydrogen evolution. Additionally, STF-1 shows activity as a pre-electrocatalyst for CO₂ conversion in aqueous media.

Topochemical N,F co-doping of mesoporous rutile TiO ₂ tunes electronic structure and visible absorption, while mesoporosity retention is critical for efficient photocatalytic O ₂ evolution.