Ryosuke Nishikubo

• Ph.D
• Assistant Professor at Osaka University

Tin-based halide perovskite solar cells (Sn PSCs) have unacceptably low open-circuit voltages owing to the severe carrier traps induced by the facile oxidation of Sn²⁺. To prevent oxidation, Sn powder is often added to the precursor solutions; however, the optimal process conditions and the detailed underlying mechanism remain elusive. Here, the PS...

The formation process of lead halide perovskite (LHP) is affected by various components such as composition, additive, under-layer, etc... Those components significantly change the perovskite quality such as crystallinity, defect density, and halide segregation. However, the comprehensive understanding of the correlation between process condition (...

Halide anion migration in organic–inorganic metal halide perovskites significantly influences the power conversion efficiency (PCE) and hysteresis of perovskite solar cells (PSCs). These materials are sensitive to various external stimuli such as light, heat, and electrical bias, highlighting the need for novel post‐manufacturing treatment methods...

The widespread use of tin dioxide (SnO2) thin films as electron transport layer (ETL) of perovskite solar cells (PSCs) has been facilitated by commercial SnO2 nanocolloid dispersion. Nevertheless, challenges such as nanoparticle agglomeration have emerged, impacting film quality and interface properties critical for PSC performance. Herein, the eff...

This article reports a purely experiment-based method to evaluate the time-dependent charge carrier mobilities in thin-film organic solar cells (OSCs) using simultaneous charge extraction by linearly increasing the voltage (CELIV) and time-resolved microwave conductivity (TRMC) measurements. This method enables the separate measurement of electron...

Considerable efforts have been devoted to the development of new organic‐inorganic hybrid perovskites as well as their passivation‐layer materials to improve the performance of solution‐processable thin‐film solar cells for practical applications. For this purpose, monocations, such as monoammonium ions, have been studied extensively as organic bui...

We designed new C 2 - and C 3 -symmetric molecules for passivating lead halide perovskite solar cells (PSCs). These unique bifacial molecules enable efficient hole transfer, defect passivation, and improved efficiency and stability.

The output of photovoltaic (PV) devices is mostly independent of the wavelength of the incident light, whereas an anomalous wavelength‐dependent photovoltaic effect (WDPE) has recently been observed in antimony chalcohalide‐chalcogenide (SbSI:Sb2S3) PVs. Remarkably, the open‐circuit voltage (VOC) exhibits a reversible change between low VOC for sho...

The rapid evolution of research on efficient and cost‐effective materials for UV photodetection is driven by their applications in environmental monitoring, medical diagnosis, security systems, and scientific research. In this study, a novel zero‐dimensional tin (IV) halide perovskite, (AEHB)2SnBr6, is synthesized for UV‐photodetector application....

Solution-processed inorganic solar cells with less toxic and earth-abundant elements are emerging as viable alternatives to high-performance lead-halide perovskite solar cells. However, the wide range of elements and process parameters impede the rapid exploration of vast chemical spaces. Here, we developed an automated robot-embedded measurement s...

High photovoltaic performance and light stability are required for the practical outdoor use of lead-halide perovskite solar cells. To improve the light stability of perovskite solar cells, it is effective to introduce a self-assembled monolayer (SAM) between the carrier transport layer and the perovskite layer. Several alternative approaches in th...

Despite the remarkable strides made in perovskite solar cell (PSC) research, the incorporation of doped hole transport materials (HTMs) presents a commercialization bottleneck. This study presents a chlorine-substituted polythiophene-based, dioxobenzodithiophene-containing conjugated polymer (P2T-Cl) as a promising dopant-free HTM. The highest occu...

Lead halide perovskites (LHPs) have a diverse compositional range owing to various employable A- and X-site ions. However, the effect of underlying charge transport layer (CTLs) on the charge transport properties in the composition-varied LHPs remains uncertain. Herein, we employed optical spectroscopies and time-resolved microwave conductivity (TR...

Organic semiconductors are well-known to exhibit high charge carrier mobility based on their spread of the π-orbital. In particular, the π-orbital overlap between neighboring molecules significantly affects their charge carrier mobility. This study elucidated the direct effect of subtle differences in the π-orbital overlap on charge carrier mobilit...

Hydrogenated molybdenum suboxide (HxMoO3-y) is a promising photothermal energy conversion (PEC) material. However, its charge carrier dynamics and underlying mechanisms remain unclear. Utilizing flash-photolysis time-resolved microwave conductivity, we investigated charge carrier-dielectric interactions in the Pt/HxMoO3-y composite. The charge reco...

Surface passivation is key to the power conversion efficiency (PCE) of organic-inorganic lead halide perovskite solar cells (PSCs). Herein, we report a novel molecular concept of a C2-symmetric syn-type bifacial donor-π-donor (D-π-D) passivation molecule (a racemic mixture of enantiomers) with hydrophobic phenyls and hydrophilic tetraethylene glyco...

Organic solar cells (OSCs) composed of a polymer and nonfullerene acceptor (NFA) have achieved dramatic improvements in power conversion efficiency (PCE), while the roles of many contributing factors are still not fully understood. Charge carrier mobility is conventionally considered a positive factor for NFA-OSC performance, yet this statement is...

The output of a photovoltaic (PV) device follows the Shockley diode equation, where its open‐circuit voltage (VOC) is marginally modulated by the photocurrent density and light intensity. Herein, an unprecedented wavelength‐dependent photovoltaic effect (WDPE) in antimony chalcoiodide (SbSI) and SbSI:Sb2S3 devices is reported, which demonstrate a r...

Organic–inorganic lead halide perovskite solar cells (PSCs) are well suited for use in spacecrafts owing to their potentially high radiation tolerance and high mass specific power. However, the optimal device structure and charge transport material (hole-transport material, HTM; electron transfer material, ETM) have remained elusive. Herein, we ext...

We provide a semi-empirical equation that quantifies the optimal layer thickness in bulk heterojunction organic solar cells, which is based on time-of-flight and time-resolved microwave conductivity measurements and photoabsorption of a film.

Crystal Engineering The machine‐learning‐assisted selective synthesis of semiconductive silver thiolate coordination polymers with segregated paths for holes and electrons is reported by Daisuke Tanaka et al. in their Research Article on page 23217.

Kristall‐Engineering Die durch maschinelles Lernen unterstützte Synthese von halbleitenden Silberthiolat‐Koordinationspolymeren mit segregierten Transportpfaden für Löcher und Elektronen wird von Daisuke Tanaka et al. im Forschungsartikel auf S. 23405 vorgestellt.

Mixed lead-tin (Pb-Sn) halide perovskites with optimum band gaps near 1.3 eV are promising candidates for next-generation solar cells. However, the performance of solar cells fabricated with Pb-Sn perovskites is restricted by the facile oxidation of Sn(ii) to Sn(iv), which induces self-doping. Maltol, a naturally occurring flavor enhancer and stron...

Coordination polymers (CPs) with infinite metal–sulfur bond networks have unique electrical conductivities and optical properties. However, the development of new (‐M‐S‐)n‐structured CPs is hindered by difficulties with their crystallization. Herein, we describe the use of machine learning to optimize the synthesis of trithiocyanuric acid (H3ttc)‐b...

Coordination polymers (CPs) with infinite metal–S bond networks have unique electrical conductivities and optical properties, thus drawing attention. However, the development of new (−M−S−) n ‐structured CPs is hindered by their crystallization difficulty. Herein, we use machine learning to optimize the synthesis of trithiocyanuric acid (H 3 ttc)‐b...

Triggered by the notable evolution of organic-inorganic metal halide perovskite solar cells (PSCs) with three-dimensional (3D) ABX3 (A: organic/inorganic cation, B: metal cation, X: halogen anion) structures, Ruddlesden-Popper two-dimensional (2D) pseudo perovskites given by An+1BnX3n+1 (n = 1, 2, …) are also becoming a material of interest, as the...

Sn-based perovskite solar cells have attracted much attention as the lead-free next generation of perovskite solar cells. However, their efficiency is still low (∼12%). One reason is that the carrier diffusion length of Sn-based perovskites is shorter than that of Pb-based perovskites. In this study, we investigated the effects of the electron tran...

Silver-bismuth-iodide (Ag-Bi-I) semiconductors have increasingly gathered much attention as an alternative to lead halide perovskites. However, Ag-Bi-I has not been thoroughly investigated owing to the complexity in its composition and solution process, and the power conversion efficiency (PCE) of its solar cell devices has still stayed at a low le...

Bismuth-based perovskites are attracting intense scientific interest due to low toxicity and excellent moisture stability compared to lead-based analogues. However, high exciton binding energy, poor charge carrier separation, and transport efficiencies lower their optoelectronic performances. To address these issues, we have integrated an electroni...

Despite recent interest in lead-free Sn iodide perovskite (ASnI3) solar cells, the role of mixed A-site cations is yet to be fully understood. Here, we report the effect of the ternary mixing of organic A-site cations (guanidium, GA; formamidinium, FA; and phenylethylamine, PEA) on the solar cell performance and charge carrier dynamics that are eva...

From the environmental and economical aspects, the development of less-toxic lead-free perovskite is an imperative challenge for next generation photovoltaics. Although bismuth-based dimer perovskite (A3B2X9) and double perovskite (A2BB’X6) (A = cation, B = Bi, B’ = Ag, X = halogen) have been considered as the plausible candidates, their power conv...

Grain size control and boundary passivation of perovskite films are the key to obtaining highly efficient perovskite solar cells. In order to accomplish both goals, semiconducting single-walled carbon nanotubes are added to perovskite films as additives, functioning both the crystal growth templates and charge bridges between the perovskite grains....

The potential of naphthalene-1,8:4,5-tetracarboxylic diimide (NDI-H) as a transparent electron-transporting material was examined. A soluble precursor was designed and synthesized having two tert-butoxycarbonyl solubilizing substituents at the imide moieties. This precursor molecule, NDI-Boc, is converted to the hydrogen substituted NDI-H by the th...

Bismuth sulfide (Bi2S3) is an attractive 2D layered, visible-light-absorbing semiconductor composed of nontoxic, abundant elements. Improving the quality of a Bi2S3 film for device applications while maintaining its intrinsic electronic properties is a challenge, as conventional film fabrication processes require a trade-off due to the uncontrolled...

Two simple methods to improve tin halide perovskite film structure are introduced, aimed at increasing the power conversion efficiency of lead free perovskite solar cells. First, a hot antisolvent treatment (HAT) was found to increase the film coverage and prevent electric shunting in the photovoltaic device. Second, it was discovered that annealin...

Two simple methods to improve tin halide perovskite film structure are introduced, aimed at increasing the power conversion efficiency of lead free perovskite solar cells. First, a hot antisolvent treatment (HAT) was found to increase the film coverage and prevent electric shunting in the photovoltaic device. Second, it was discovered that annealin...

Photon upconversion constitutes an exceptionally rich area of research in photonics and electronics, where low-energy light is converted to high-energy light through nonlinear processes represented by two-photon absorption (TPA) and triplet–triplet annihilation (TTA). Here, we report a cascade process of TPA in inorganic perovskite quantum dots (PQ...

Organic–inorganic metal halide perovskites (MHPs) exhibit prominent electronic and optical properties benefiting the performance of solar cells and light-emitting diodes. However, the dielectric properties of these materials have remained poorly understood, despite probably influencing delayed charge recombination and device capacitance. Herein, we...

Herein, we report use of [Li+@C60]TFSI-as a dopant for spiro-MeOTAD in lead halide perovskite solar cells. This approach gave an air stability nearly 10-fold that of conventional devices using Li+TFSI-. Such high stability is attributed to the hydrophobic nature of [Li+@C60]TFSI-repelling moisture and absorbing intruding oxygen, thereby protecting...

Herein, we report use of [Li⁺@C60]TFSI⁻ as a dopant for spiro-MeOTAD in lead halide perovskite solar cells. This approach gave an air stability nearly 10-fold that of conventional devices using Li⁺TFSI⁻. Such high stability is attributed to the hydrophobic nature of [Li⁺@C60]TFSI⁻ repelling moisture and absorbing intruding oxygen, thereby protectin...

A series of solvent-coordinated tin halide complexes were prepared as impurity-free precursors for tin halide perovskites, and their structures were determined by single-crystal X-ray diffraction analysis. Using these precursors, the tin halide perovskites, MASnI3 and FASnI3, were prepared, and their electronic structures and photophysical properti...

We report an efficient approach to attain multi-functional π-conjugated polymers (P1-P3) by controlling the degree of fluorination (0F, 2F and 4F) on side-chain linked to benzodithiophene unit of π-conjugated polymer. Most promising changes were noticed in photo physical and photovoltaic properties upon varying the degree of fluorine substitution o...

The development of lead-free, tin-based perovskite solar cells is becoming a pervasive topic; however, the inherent instabilities of such cells have prevented a boost of their power conversion efficiency and a deeper understanding of their fundamental properties. By using the photoelectron yield spectroscopy (PYS) and flash-photolysis time-resolved...

To acknowledge exceptionally productive flexible perovskite solar cells, low-temperature-processable efficient organic hole transporting materials are very significant for the emerging photovoltaic research. A new organic small molecular hole transporting material (N-(4-(9H-carbazol-9-yl)phenyl)-7-(4-(bis(4-methoxyphenyl)amino)phenyl)-N-(7-(4-(bis(...

Upon cooling and heating, organic–inorganic perovskite nanoparticles are reversibly decomposed and formed through the lower-critical-solution-temperature phenomenon. Akinori Saeki and co-workers demonstrate an aurora-like photoemissive object in article number 1700047, and reveal the roles of the involved chemicals (methylammonium cation, lead, hal...

Lead halide perovskites have shown much promise for high-performing solar cells due to their inherent electronic nature, and though the color of bright-light emitters based on perovskite nanoparticles can be tuned by halide mixing and/or size control, dynamic switching using external stimuli remains a challenge. This article reports an unprecedente...

Perovskite solar cells (PSCs) and organic solar cells (OSCs) are promising renewable light-harvesting technologies with high performance, but the utilization of hazardous dopants and high boiling additives is harmful to all forms of life and the environment. Herein, new multirole π-conjugated polymers (P1-P3) are developed via a rational design app...