Ce-Doped SnO2 Electron Transport Layer for Minimizing Open Circuit Voltage Loss in Lead Perovskite Solar Cells.

In the planar heterostructure of perovskite-based solar cells (PSCs), tin oxide (SnO2) is a material that is often used as the electron transport layer (ETL). SnO2 ETL exhibits favorable optical and electrical properties in the PSC structures. Nevertheless, the open circuit voltage (VOC) depletion occurs in PSCs due to the defects arising from the high oxygen vacancy on the SnO2 surface and the deeper conduction band (CB) energy level of SnO2. In this research, a cerium (Ce) dopant was introduced in SnO2 (Ce-SnO2) to suppress the VOC loss of the PSCs. The CB minimum of SnO2 was shifted closer to that of the perovskite after the Ce doping. Besides, the Ce doping effectively passivated the surface defects on SnO2 as well as improved the electron transport velocity by the Ce-SnO2. These results enabled the power conversion efficiency (PCE) to increase from 21.1% (SnO2) to 23.0% (Ce-SnO2) of the PSCs (0.09 cm2 active area) with around 100 mV of improved VOC and reduced hysteresis. Also, the Ce-SnO2 ETL-based large area (1.0 cm2) PSCs delivered the highest PCE of 22.9%. Furthermore, a VOC of 1.19 V with a PCE of 23.3% was demonstrated by Ce-SnO2 ETL-based PSCs (0.09 cm2 active area) that were treated with 2-phenethylamine hydroiodide on the perovskite top surface. Notably, the unencapsulated Ce-SnO2 ETL-based PSC was able to maintain above 90% of its initial PCE for around 2000 h which was stored under room temperature condition (23-25 °C) with a relative humidity of 40-50%.

Inhibition of Sn2+ Oxidation in FASnI3 Perovskite Precursor Solution and Enhanced Stability of Perovskite Solar Cells by Reductive Additive.

Tin-based halide perovskite solar cells (Sn-PSCs) have attracted a progressive amount of attention as a potential alternative to lead-based PSCs (Pb-PSCs). Sn-perovskite films are fabricated by a solution process spin-coating technique. However, the efficiency of these devices varies significantly with the different batches of precursor solution due to the poor chemical stability of SnI2-DMSO and the oxidation of Sn2+ to Sn4+. This study investigated the origin of Sn2+ oxidation before film formation, and it was identified that the ionization of SnI2 in dimethyl sulfoxide (DMSO) causes the oxidation of free Sn2+ and I- ions. To address these issues, this study introduces the reductive additive 4-fluorophenylhydrazine hydrochloride (4F-PHCl) in the FASnI3 perovskite precursor solution. The hydrazine functional (-NH-NH2) group converted detrimental Sn4+ and I2 defects back to Sn2+ and I- in precursor solution while retaining the properties of the perovskite solution. Furthermore, the addition of 4F-PHCl in the precursor solution effectively slows the crystallization process, enhancing the crystallinity of FASnI3 perovskite films and guaranteeing the Sn2+/I- stoichiometric ratio, ultimately leading to a power conversion efficiency (PCE) of 10.86%. The hydrophobic fluorinated benzene ring in 4F-PHCl ensures moisture stability in perovskite films, allowing unencapsulated PSCs to retain over 92% of their initial PCE in an N2-filled glovebox for 130 days. Moreover, the 4F-PHCl-modified encapsulated PSCs showed superior operational stability for 420 h and maintained 95% of their initial PCE for 300 h under maximum power point tracking at 1 sun continuous illumination. This study's findings provide a promising pathway to create a controlled Sn-based perovskite precursor solution for highly reproducible and stable Pb-free Sn-PSCs.

Chemical passivation of the under coordinated Pb2+ defects in inverted planar perovskite solar cells via ß-diketone Lewis base additives.

Hybrid organic-inorganic perovskite solar cells (PSCs) are promising new generations of solar cells, which is low in cost with high power conversion efficiency (PCE). However, PSCs suffer from structural defects generated from the under coordinated ions at the surface, which limits their photovoltaic performances. Herein we report, two ß-diketone Lewis base additives 2,4-pentanedione and 3-methyl-2,4-nonanedione within the chlorobenzene anti-solvent to passivate the surface defects generated from the under coordinated Pb2+ ions in CH3NH3PbI3 perovskite films. The incorporation of the two ß-diketone passivators could successfully enhance the open-circuit voltage of the PSCs by 52 mV and 17 mV for 3-methyl-2,4-nonanedione and 2,4-pentanedione, respectively, with improved PCE by 45% for 3-methyl-2,4-nonanedione compared to the pristine PSC. This enhancement in the photovoltaic performance of the PSCs can be attributed to passivation of the defects through the interaction between two carbonyl groups of the ß-diketone Lewis base additives and the under coordinated Pb2+ defects in the perovskite film, which improved the PSCs PCE and stability.

High-Pressure Raman Study of n-Octane up to 15 GPa.

The high-pressure (HP) phase transition and conformational change of n-octane (hereafter abbreviation as n-C8) up to 15.3 GPa were studied using Raman spectroscopy to investigate the relationship between the HP phase state and the alkyl chain length of n-alkanes. The Raman spectral analysis of n-C8 indicated that the liquid-solid transition (solidification) occurs at ∼0.9 GPa and that the corresponding transition pressure of n-alkanes depends on their density. Further pressurization at ∼4 GPa increased the population of the gauche conformer, while the solid (order)-amorphous transition occurred at ∼6 GPa along with a change in the full width at half maximum of the ruby R1 fluorescence line. The comparison of our findings with previously reported results suggested that the even-odd effect in the HP phase transition after solidification of n-alkanes appears between n-C7 and n-C8 as their HP phase transition up to ∼15 GPa was different.

How does the flexibility of pyrrolidinium cations affect the phase behaviour of 1-alkyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide homologues under stressful conditions?

We conducted high-pressure Raman spectroscopy measurements on a series of 1-alkyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([Pyr1n][TFSI], n = 3, 4, 6 and 8) homologues that have different alkyl chain lengths, n, at room temperature. The results showed that all [Pyr1n][TFSI] samples formed a glassy state in which the glass transition pressure (pg) slightly increased with an increase in n. This tendency is similar to prior results of high-pressure glass formation of [Cnmim][TFSI], although the pgs for [Pyr1n][TFSI] are larger than those for [Cnmim][TFSI] with corresponding n by ∼0.5 GPa. We discuss the local structural changes occurring in [Pyr1n][TFSI] in view of the conformational changes of the Pyr+1n cation and TFSI- anion.

Long Periodic Structure of a Room-Temperature Ionic Liquid by High-Pressure Small-Angle X-Ray Scattering and Wide-Angle X-Ray Scattering: 1-Decyl-3-Methylimidazolium Chloride.

The Bragg reflections of 1-decyl-3-methylimidazolium chloride ([C10 mim][Cl]), a room-temperature ionic liquid, are observed in a lowly scattered wavevector (q) region using high-pressure (HP) small-angle X-ray scattering methods. The HP crystal of [C10 mim][Cl] was characterized by an extremely long periodic structure. The peak position at the lowest q (1.4 nm-1 ) was different from that of the prepeak observed in the liquid state (2.3 nm-1 ). Simultaneously, Bragg reflections at high-q were detected using HP wide-angle X-ray scattering. The longest lattice constant was estimated to be 4.3 nm using structural analysis. The crystal structure of HP differed from that of the low-temperature (LT) crystal and the LT liquid crystal. With increasing pressure, Bragg reflections in the high-q component became much broader, and were accompanied by phase transition, although those in the low-q component were observed to be relatively sharp.

High-pressure glass formation of a series of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide homologues.

We investigated the stability of the liquid phase of a series of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Cnmim][TFSI]) homologues with different alkyl chain lengths for 3 ≤ n ≤ 10 at room temperature. We found that all [Cnmim][TFSI] samples (n = 3-10) formed a glassy state when pressure was applied. Intriguingly, the glass transition pressure (pg) slightly increases up to n = 5, reaches a plateau at n ≧ 8, and increases again at n = 10. This is completely different from the high-pressure glass formation of [Cnmim][BF4], where the pg decreases as n increases. We discussed the local structural changes occurring in [Cnmim][TFSI] in view of the conformational changes of the cation and anion, and small-angle X-ray scattering data. It seems that [Cnmim][TFSI] is resistant to external pressure and retains its local liquid structure by conformational adjustments of the cation and anion.

Luminescence color control and quantum-efficiency enhancement of colloidal Si nanocrystals by pulsed laser irradiation in liquid.

We demonstrate the emission color change of white-emitting chlorine-terminated silicon nanocrystals (Cl:Si-ncs) to blue-emitting carbon-terminated silicon nanocrystals (C:Si-ncs), together with the enhancement of the luminescence quantum efficiency from 7% to 13%, by post-laser ablation in 1-octene. Such changes of the PL properties are caused by the size reduction of Si-nc and efficient surface passivation by hydrocarbons, resulting from a high reactivity of 1-octene in the laser-ablation and subsequent nanoparticle-formation processes. Furthermore, the second post-laser irradiation of the C:Si-ncs in trichloroethylene reversibly results in the formation of the Cl:Si-ncs. The preparation yield of C:Si-ncs via the post-laser ablation of Cl:Si-ncs is higher than that of C:Si-ncs directly prepared only by the laser ablation of PSi in 1-octene. This high preparation yield is due to the high laser-ablation efficiency in trichloroethylene compared with 1-octene, which is attributed to the low heat loss of the solvent in the laser-ablation process.

Conformational adjustment for high-pressure glass formation of 1-alkyl-3-methylimidazolium tetrafluoroborate.

The conformational stability of 1-alkyl-3-methylimidazolium tetrafluoroborate ([Cnmim][BF4], n = 3-8) under high pressure was investigated using Raman spectroscopy to reveal the preferential role of the alkyl-chain length (n) in high-pressure glass transition. To evaluate this, we determined the intensity ratio (r) and differences in the partial molar volume (ΔVtrans→gauche) between the whole trans and gauche conformers of the [Cnmim] cation using Raman intensities. Interestingly, both values were classified into a two alkyl-chain length region at the border of n = 5. The coulombic interaction (cation-anion interaction) for the conformational stability is the predominant factor below n = 5 (the cation-head portion: alkyl carbon number C < 5), and the alkyl-chain packing effect (cation-cation interaction) is the predominant factor above n = 5 (the cation-tail portion: C > 5). In combination with the conformational preference of the [Cnmim] cation under a high-pressure glassy state, the alkyl chain displays a preferential role, i.e., an increase in the gauche conformer of [Cnmim][BF4] adjusts to avoid crystallization (the conformational adjustment effect). In the presence of the coulombic interaction, the preferential role of the flexible alkyl chain is an important key to elucidate the mechanism of the complicated high-pressure phase transition behavior of ionic liquids.

Synthesis and Properties of Poly(Isothianaphthene Methine)s with Chiral Alkyl Chain.

We synthesized poly(isothianaphthene methine)s with chiral alkyl chains in the substituent. Resultant polymers are soluble in THF and CHCl3. Structure of the polymers was characterized with FT-IR, FT-Raman, and UV-Vis-NIR optical absorption spectroscopy. They showed low-bandgap both in solution and in a form of film. Optical activity of the polymers was confirmed with optical rotatory dispersion. Doping effects on the polymer were also examined with UV-Vis-NIR spectroscopy and ESR measurement.

Molecular alignment and energy-level diagram at heteromolecular interface of quaterrylene and terrylene-3,4,11,12-tetracarboximide.

Heteromolecular layers consisting of quaterrylene (QT) and terrylene-3,4,11,12-tetracarboximide (TTCDI-C12) were prepared on SiO2 surfaces and the electronic energy level alignment at TTCDI-C12/QT interface was examined. TTCDI-C12 layers were grown in nearly perpendicular orientation on QT layers by an ultraslow deposition technique, thereby achieving formation of a well-defined TTCDI-C12/QT interface. Atomic force microscopy (AFM) measurements ensured excellent surface flatness of each layer, surface roughnesses of which were comparable to that of pristine SiO2. Energy level alignment at the heteromolecular interface was evaluated by using ultraviolet photoelectron spectroscopy (UPS) and optical absorption measurements. No shift in energy level was served at the heteromolecular interface, indicating that charge transfer does not occur and a dipole moment is not formed at the well-defined TTCDI-C12/QT interface.

Large payloads of gold nanoparticles into the polyamine network core of stimuli-responsive PEGylated nanogels for selective and noninvasive cancer photothermal therapy.

A biocompatible photothermal nanomedicine based on a PEGylated nanogel containing gold nanoparticles (GNPs) in a cross-linked network core of stimuli-responsive poly[2-(N,N-diethylamino)ethyl methacrylate] (PEAMA) gel for cancer photothermal therapy (PTT) was prepared through the reduction of Au(iii) ions without any reducing agents. The influence of the reduction conditions, such as pH, temperature, and N/Au ratio (molar ratio of the amino groups in the PEGylated nanogel to the Au(iii) ions), on the formation of the GNPs in the stimuli-responsive PEAMA gel core (reducing environment) was also studied. Note that the PEGylated nanogel containing GNPs prepared at pH 6, 60 degrees C and N/Au = 1 (PEGylated GNG (1)) was found to have the highest GNP-loading capacity with a diameter of about 8 nm, as observed by TEM; viz., about 27 GNPs formed in a single PEAMA gel core. PEGylated GNG (1) showed a remarkable photothermal efficacy (DeltaT = 7.7 degrees C) under irradiation with Ar ion (Ar(+)) laser (514.5 nm) at a fluence of 39 W cm(-2) for 6 min (14 kJ cm(-2)). Note that PEGylated GNG (1) showed non-cytotoxicity in the absence of irradiation with Ar(+) laser (480 microg mL(-1): > 90% cell viability), whereas pronounced cytotoxicity (IC(50) = 110 microg mL(-1)) was observed for PEGylated GNG (1) under irradiation with Ar(+) laser at a fluence of 26 W cm(-2) for 5 min (7.8 kJ cm(-2)), because of the heat-generation from the GNPs in the cells, which resulted in selective and noninvasive cancer PTT. Thus, PEGylated GNG (1), which has a high GNP-loading capacity, would be a promising nanomedicine for cancer PTT.

Catalytic functions of Mo/Ni/MgO in the synthesis of thin carbon nanotubes.

The functions and structures of Mo/Ni/MgO catalysts in the synthesis of carbon nanotubes (CNTs) have been investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Thin 2-5-walled CNTs with high purities (over 90%) have been successfully synthesized by catalytic decomposition of CH(4) over Mo/Ni/MgO catalysts at 1073 K. It has been found that the yield of CNTs as well as the outer diameter or thickness correlates well with the contents of these three elements. The three components Mo, Ni, and MgO are all necessary to synthesize the thin CNTs at high yields since no catalytic activity was observed for CNT synthesis when one of these components was not present. The outer diameter of the CNTs increases from 4 to 13 nm and the thickness of graphene layers also increases with increasing Mo content at a fixed Ni content, while the inner diameter stays at 2-3 nm regardless of their contents. Furthermore, the average outer diameter is in good agreement with the average particle size of metal catalyst. That is, the thickness or the outer diameter can be controlled by selecting the composition of the Mo/Ni/MgO catalysts. XRD analyses have shown that Mo and Ni form a Mo-Ni alloy before CNT synthesis, while the Mo-Ni alloy phase is separated into Mo carbide and Ni. These alloy particles are supported on MgO cubic particles 15-20 nm in width. It has been found that only small Mo-Ni alloy particles 2-16 nm in size catalyze CNT synthesis, with larger particles over 15 nm exhibiting no activity. Mo carbide and Ni should play different roles in the synthesis of the thin CNTs, in which Ni is responsible for the dissociation of CH(4) into carbon and Mo(2)C works as a carbon reservoir.

Raman spectroscopy of hot dense hydrogen.

High P-T Raman measurements of solid and fluid hydrogen to above 1100 K at 70 GPa and to above 650 K in 150 GPa range, conditions previously inaccessible by static compression experiments, provide new insight into the behavior of the material under extreme conditions. The data give a direct measure of the melting curve that extends previous optical investigations by up to a factor of 4 in pressure. The magnitude of the vibron frequency temperature derivative (dnu/dT)(P) increases by a factor of approximately 30 over the measured pressure range, indicating an increase in intrinsic anharmonicity and weakening of the molecular bond.