Luis Ono | Okinawa Institute of Science and Technology (original) (raw)

Papers by Luis Ono

Advanced Materials

Further enhancing the operational lifetime of inverted‐structure perovskite solar cells (PSCs) is... more Further enhancing the operational lifetime of inverted‐structure perovskite solar cells (PSCs) is crucial for their commercialization, and the design of hole‐selective contacts at the illumination side plays a key role in operational stability. In this work, the self‐anchoring benzo[rst]pentaphene (SA‐BPP) is developed as a new type of hole‐selective contact toward long‐term operationally stable inverted PSCs. The SA‐BPP molecule with a graphene‐like conjugated structure shows a higher photostability and mobility than that of the frequently‐used triphenylamine and carbazole‐based hole‐selective molecules. Besides, the anchoring groups of SA‐BPP promote the formation of a large‐scale uniform hole contact on ITO substrate and efficiently passivate the perovskite absorbers. Benefiting from these merits, the champion efficiencies of 22.03% for the small‐sized cells and 17.08% for 5 × 5 cm2 solar modules on an aperture area of 22.4 cm2 are achieved based on this SA‐BPP contact. Also, the...

Small

Heterogeneous catalytic mediators have been proposed to play a vital role in enhancing the multio... more Heterogeneous catalytic mediators have been proposed to play a vital role in enhancing the multiorder reaction and nucleation kinetics in multielectron sulfur electrochemistry. However, the predictive design of heterogeneous catalysts is still challenging, owing to the lack of in‐depth understanding of interfacial electronic states and electron transfer on cascade reaction in Li–S batteries. Here, a heterogeneous catalytic mediator based on monodispersed titanium carbide sub‐nanoclusters embedded in titanium dioxide nanobelts is reported. The tunable catalytic and anchoring effects of the resulting catalyst are achieved by the redistribution of localized electrons caused by the abundant built‐in fields in heterointerfaces. Subsequently, the resulting sulfur cathodes deliver an areal capacity of 5.6 mAh cm−2 and excellent stability at 1 C under sulfur loading of 8.0 mg cm−2. The catalytic mechanism especially on enhancing the multiorder reaction kinetic of polysulfides is further dem...

The Japan Society of Applied Physics, 2016

Thin films of spiro-OMeTAD doped by LiTFSI were studied under controlled environments of H2O vapo... more Thin films of spiro-OMeTAD doped by LiTFSI were studied under controlled environments of H2O vapor, O2 and ambient air using current-voltage (I-V) measurements, x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS). I-V measurements show that exposing the LiTFSI doped films to H2O vapor leads to irreversible increased conductivity, whereas the O2 exposed films show reversible enhanced conductivity. XPS results show that H2O is the constituent component in ambient air that makes the LiTFSI dopants to re-distribute across the spiro-OMeTAD films. 第63回応用物理学会春季学術講演会講演予稿集 (2016 東京工業大学大岡山キャンパス) 19a-P5-21

2019 26th International Workshop on Active-Matrix Flatpanel Displays and Devices (AM-FPD), 2019

On the basis of concerted research efforts worldwide, there is no doubt that outstanding power co... more On the basis of concerted research efforts worldwide, there is no doubt that outstanding power conversion efficiency (PCE) can be achieved in perovskite solar cells. However, to move forward this technology towards commercialization, developments of strategies to achieve long term stability is important. At OIST, a team of researchers in the Energy Materials and Surface Sciences Unit has been making concerted efforts to develop processes aiming at high PCE, high-throughput, minimum batch-to-batch variation, compatible with large-area perovskite solar cells and modules, low toxicity, and long-term stability. Optimization of hole transport materials (HTMs) is important for enhancing solar power conversion efficiency and improving stability. In this talk, we will present our latest understanding of fundamental interactions between Li-bis(trifluoromethanesulfonyl)-imide (LiTFSI), 4-tert-butylpyridine (t-BP) and spiro-MeOTAD and how different gas exposures (e.g., exposure to O2, H2O, N2)...

Energy & Environmental Science, 2021

Our scanning tunneling microscopy and density functional theory studies show that the Cl incorpor... more Our scanning tunneling microscopy and density functional theory studies show that the Cl incorporation plays a crucial role in the surface stability of the metal halide perovskite CH3NH3PbI3.

Journal of Materials Chemistry A, 2020

Rapid hybrid chemical vapor deposition is developed to fabricate perovskite solar modules with a ... more Rapid hybrid chemical vapor deposition is developed to fabricate perovskite solar modules with a markedly reduced time while maintaining high performance.

Advanced Energy Materials, 2021

In addition to high efficiencies, upscaling and long‐term operational stability are key pre‐requi... more In addition to high efficiencies, upscaling and long‐term operational stability are key pre‐requisites for moving perovskite solar cells toward commercial applications. In this work, a strategy to fabricate large‐area uniform and dense perovskite films with a thickness over one‐micrometer via a two‐step coating process by introducing NH4Cl as an additive in the PbI2 precursor solution is developed. Incorporation of NH4Cl induces the formation of the intermediate phases of x[NH4+]·[PbI2Clx]x− and HPbI3−xClx, which can effectively retard the crystallization rate of perovskite leading to uniform and compact full‐coverage perovskite layers across large areas with high crystallinity, large grain sizes, and small surface roughness. The 5 × 5 and 10 × 10 cm2 perovskite solar modules (PSMs) based on this method achieve a power conversion efficiency (PCE) of 14.55% and 10.25%, respectively. These PSMs also exhibit good operational stability with a T80 lifetime (the time during which the sola...

Extended Abstracts of the 2018 International Conference on Solid State Devices and Materials, 2018

The Journal of Physical Chemistry Letters, 2020

All-inorganic halide perovskites are promising materials for optoelectronic applications. The sur... more All-inorganic halide perovskites are promising materials for optoelectronic applications. The surface or interface structure of the perovskites plays a crucial role in determining the optoelectronic conversion efficiency, as well as the material stability. A thorough understanding of surface atomic structures of the inorganic perovskites and their contributions to their optoelectronic properties and stability is lacking. Here we show a scanning tunneling microscopy investigation on the atomic and electronic structure of CsPbBr 3 perovskite. Two different surface structures with a stripe and an armchair domain are identified, which originates from a complex interplay between Cs cations and Br anions. Our findings are further supported and correlated with density functional theory calculations and photoemission spectroscopy measurements. The stability evaluation of photovoltaic devices indicates a higher stability for CsPbBr 3 in comparison with MAPbBr 3 , which is closely related to the low volatility of Cs from the perovskite surface.

Matter, 2019

The existence of a mass oxidation of Sn 2+ that takes place mainly during preparation of precurso... more The existence of a mass oxidation of Sn 2+ that takes place mainly during preparation of precursor solutions and fabrication of films creates a lead-free solar cell of low open-circuit voltage, which leads to low PCE. To reduce the oxidation process, we employed an innovative crystal fabrication method with anti-solventfree recrystallization technology. As a result, to the best of our knowledge, both spin-coated and printed lead-free solar cells based on FASnI 3 achieved the highest 3D-based PCE to date.

Advanced Energy Materials, 2019

ABX3 type metal halide perovskite solar cells (PSCs) have shown efficiencies over 25%, rocketing ... more ABX3 type metal halide perovskite solar cells (PSCs) have shown efficiencies over 25%, rocketing toward their theoretical limit. To gain the full potential of PSCs relies on the understanding of the device working mechanisms and recombination, the material quality, and the match of energy levels in the device stacks. In this review, the importance of designing PSCs from the viewpoint of surface/interface science studies is presented. For this purpose, recent case studies are discussed to demonstrate how probing of local heterogeneities (e.g., grains, grain boundaries, atomic structure, etc.) in perovskites by surface science techniques can help correlate material properties and PSC device performance. At the solar cell device level with active areas larger than millimeter scale, the ensemble average measurement techniques can characterize the overall average properties of perovskite films as well as their adjacent layers and provide clues to understand better the solar cell paramete...

Energy Technology, 2019

Inorganic perovskite solar cells (PSCs) have attracted enormous attention during the past 5 years... more Inorganic perovskite solar cells (PSCs) have attracted enormous attention during the past 5 years. Many advanced strategies and techniques have been developed for fabricating inorganic PSCs with improved efficiency and stability to realize commercial applications. CsPbBr3 is one of the representative materials of inorganic perovskites and has demonstrated excellent stability against thermal and high humidity environmental conditions. The power conversion efficiency of CsPbBr3‐based PSCs has increased significantly from 5.95% in 2015 to 10.91%, and the storage stability under moisture (≈80% relative humidity) and heat (≈80 °C) is more than 2000 h. The outstanding performance of CsPbBr3 PSCs shows great potential in light‐to‐electricity conversion applications. In this review, recent developments of CsPbBr3‐based PSCs including the physico‐chemical as well as optoelectronic properties, processing techniques for fabricating CsPbBr3 films, derivative phase structures, efficiency, and st...

Science, 2019

Tetragonal phases for perovskite solar cells The power conversion efficiencies (PCEs) of all-inor... more Tetragonal phases for perovskite solar cells The power conversion efficiencies (PCEs) of all-inorganic perovskites are lower than those of materials with organic cations. This is in part because these materials have larger bandgaps. The cubic crystal phases of these materials also exhibit poor stability. Wang et al. synthesized the tetragonal β-phase of CsPbI 3 from HPbI 3 and CsI. The material exhibited higher stability and a more favorable bandgap, which allowed for PCEs of 15%. Passivation of the surface trap state with choline iodide boosted PCEs to 18%. Science , this issue p. 591

Nature Energy, 2019

Nowadays the major factors determining commercialization of lead halide perovskite photovoltaic t... more Nowadays the major factors determining commercialization of lead halide perovskite photovoltaic technology are shifting from solar cell performance to stability, reproducibility, up-scaling, and in particular the concern of Pb leakage during solar cell operation. Here we simulate a realistic scenario that the perovskite solar modules with different encapsulation methods are damaged to a typical extent by mechanical impact (according to the modified FM 44787 standard) and quantitatively measure the lead leakage rates from the damaged modules. We demonstrate that an epoxy resin (ER) based encapsulation method reduces the Pb leakage rate by a factor of 375 compared to the encapsulation method using a glass cover with the UV-resin cured at the module edges. The excellent Pb leakage prevention characteristics is due to the self-healing property of ER and increased mechanical strength. These findings strongly suggest lead halide perovskite photovoltaic products can be used with minimal Pb leakage if appropriate encapsulation is employed.

Journal of Materials Chemistry A, 2019

Large area and stable mixed-cation perovskite solar modules are fabricated via hybrid-CVD, which ... more Large area and stable mixed-cation perovskite solar modules are fabricated via hybrid-CVD, which represents a step forward towards commercialization.

Journal of the American Chemical Society, 2019

Increasing the stability of perovskites is essential for their integration in commercial photovol... more Increasing the stability of perovskites is essential for their integration in commercial photovoltaic devices. Halide mixing is suggested as a powerful strategy toward stable perovskite materials. However, the stabilizing effect of the halides critically depends on their distribution in the mixed compound, a topic that is currently under intense debate. Here we successfully determine the exact location of the I and Cl in the mixed CH 3 NH 3 PbBr 3-y I y and CH 3 NH 3 PbBr 3-z Cl z perovskite lattices and correlate it with the enhanced stability we find for the latter. By combining scanning tunneling microscopy (STM) and density functional theory (DFT), we predict that for low ratios, iodine and chlorine incorporation have opposite effects on the electronic properties and stability of the CH 3 NH 3 PbBr 3 perovskite material. In addition, we determine an ideal halide ratio for stability increase without detrimental bandgap modification, providing an important direction for the fabrication of stable perovskite devices. The increased material stability induced by chlorine incorporation is verified by performing photoelectron spectroscopy on a device architecture. Our findings provide an answer to the current debate on halide incorporation and demonstrate their direct influence on device stability.

Nature Communications, 2019

There has been an urgent need to eliminate toxic lead from the prevailing halide perovskite solar... more There has been an urgent need to eliminate toxic lead from the prevailing halide perovskite solar cells (PSCs), but the current lead-free PSCs are still plagued with the critical issues of low efficiency and poor stability. This is primarily due to their inadequate photovoltaic properties and chemical stability. Herein we demonstrate the use of the lead-free, all-inorganic cesium tin-germanium triiodide (CsSn0.5Ge0.5I3) solid-solution perovskite as the light absorber in PSCs, delivering promising efficiency of up to 7.11%. More importantly, these PSCs show very high stability, with less than 10% decay in efficiency after 500 h of continuous operation in N2 atmosphere under one-sun illumination. The key to this striking performance of these PSCs is the formation of a full-coverage, stable native-oxide layer, which fully encapsulates and passivates the perovskite surfaces. The native-oxide passivation approach reported here represents an alternate avenue for boosting the efficiency an...

Advanced Functional Materials, 2018

Stability and scalability have become the two main challenges for perovskite solar cells (PSCs) w... more Stability and scalability have become the two main challenges for perovskite solar cells (PSCs) with the research focus in the field advancing toward commercialization. One of the prerequisites to solve these challenges is to develop a cost‐effective, uniform, and high quality electron transport layer that is compatible with stable PSCs. Sputtering deposition is widely employed for large area deposition of high quality thin films in the industry. Here the composition, structure, and electronic properties of room temperature sputtered SnO2 are systematically studied. Ar and O2 are used as the sputtering and reactive gas, respectively, and it is found that a highly oxidizing environment is essential for the formation of high quality SnO2 films. With the optimized structure, SnO2 films with high quality have been prepared. It is demonstrated that PSCs based on the sputtered SnO2 electron transport layer show an efficiency up to 20.2% (stabilized power output of 19.8%) and a T80 operati...