We synthesized single-crystalline Sn-based oxides for use as electron-transporting layers (ETLs) in perovskite solar cells (PSCs). The control of the Zn-to-Sn cation ratio (Zn/Sn = 0–2) in a fixed concentration of hydrazine solution leads to the formation of various types of Sn-based oxides, i.e., spherical SnO2 and Zn2SnO4 nanoparticles (NPs), SnO2 nanorods, and Zn2SnO4 nanocubes. In particular, a ratio of Zn/Sn = 1 results in nanocomposites of single-crystalline SnO2 nanorods and Zn2SnO4 nanocubes. This is related to the concentration of free hydrazine unreacted with Zn and Sn ions in the reaction solution, because the resulting OH− concentration affects the growth rate of intermediate phases such as ZnSn(OH)6, Zn(OH)42− and Sn(OH)62−. Additionally, we propose plausible pathways for the formation of Sn-based oxides in hydrazine solution. The Sn-based oxides are applied as ETLs and annealed at a low temperature below 150 °C in PSCs. The PSCs fabricated by using the nanocomposite ETLs consisting of single-crystalline SnO2 nanorods and Zn2SnO4 nanocubes exhibit superior device performance to TiO2-based PSCs due to their excellent charge collection ability and optical properties, achieving a power conversion efficiency of ≥17%.

We report the presence of defects in CH3NH3PbI3, which is one of the main factors that deteriorates the performance of perovskite solar cells. Although the efficiency of the perovskite solar cells has been improved by curing defects using various methods, deeply trapped defects in the perovskite layer have not been systematically studied, and their function is still unclear. The comparison and analysis of defects in differently prepared perovskite solar cells reveals that both solar cells have two kinds of deep level defects (E1 and E2). In the one-pot solution processed solar cell, the defect state E1 is dominant, while E2 is the major defect in the solar cell prepared using the cuboid method. Since the energy level of E1 is higher than that of E2, the cuboid solar cell shows higher open-circuit voltage and efficiency.

We fabricated green–red (GR) and blue–red (BR) bilayer stacked quantum dots (QDs) using electrospray deposition. Along with steady state and time-resolved photoluminescence (PL), subnanosecond donor PL decay and corresponding acceptor PL rise signals were observed, which are ascribed to the energy transfer between different visible QDs (heterotransfer). The heterotransfer rates were estimated as (0.57 ± 0.01 ns)−1 and (0.65 ± 0.02 ns)−1 for GR and BR systems, respectively, which agree well with theoretical calculations. Owing to their geometrical proximity, mixed QD layers with GR and BR showed qualitatively higher heterotransfer efficiencies of 64% and 81%, compared to stacked QD layers, which have efficiencies of 23% and 64%, respectively.

Sn–porphyrin networks were engineered on the surface of a thin layer chromatography (TLC) plate via Sonogashira coupling of the Sn–porphyrin building block and 1,4-diiodobenzene. The Sn–porphyrin film showed a strong Soret band absorption at 422 nm, emission at 600–630 nm, and excellent sensing performance toward nitrophenols in water.

Hollow microporous organic networks were prepared by using silica spheres as the template and tris(4-ethynylphenyl)amine and 2,6-diiodo-9,10-anthraquinone as the building blocks for the Sonogashira coupling. The resultant materials bearing triphenylamine and anthraquinone moieties showed efficient visible light absorption and catalytic activities in the photochemical oxidative coupling of benzylamines. Through the comparison studies of hollow and nonhollow catalytic materials, the diffusion pathway effect of the substrates was clearly observed in the photochemical conversion of benzylamines.

To understand the role of the dye/oxide interface, a model system using a nanocrystalline SnO2 and 3-hexyl thiophene based MK-2 dye is proposed. A thin interfacial TiO2 blocking layer (IBL) is introduced in between SnO2 and MK-2 and its effects on photocurrent–voltage, electron transport-recombination, and density of states (DOS) are systematically investigated. Compared to the bare SnO2 film, the insertion of IBL leads to a 14-fold improvement in the power conversion efficiency (PCE) despite little change in the dye adsorption amount, which is due to the 7-fold and 2-fold increase in the photocurrent density and voltage, respectively. The charge collection efficiency is substantially improved from 38% to 96% mainly due to the increase in the electron lifetime. The IBL is also found to enhance the dye regeneration efficiency as confirmed by the 15-fold faster dye bleaching recovery dynamics. The recombination resistance increases and the DOS decreases after surface modification of SnO2, which is responsible for the doubly increased voltage. This study suggests that the interfacial layer between the oxide and the dye plays a crucial role in retarding recombination, improving charge collection efficiency, increasing diffusion length, accelerating dye regeneration and narrowing the density of states.

This work shows that microporous organic network (MON) chemistry can be successfully applied for the development of a visible light-induced hydrogen production system. A visible light harvesting MON (VH-MON) was prepared by the Knoevenagel condensation of tri(4-formylphenyl)amine with [1,1′-biphenyl]-4,4′-diacetonitrile. Scanning electron microscopy (SEM) showed a 1D rod morphology of the VH-MON. Analysis of a N2 sorption isotherm showed a 474 m2 g−1 surface area and microporosity. Solid phase 13C nuclear magnetic resonance (NMR) and infrared (IR) absorption spectroscopy, and elemental analysis support the expected network structure. The VH-MON showed visible light absorption in 400–530 nm and vivid emission at 542 nm. The HOMO and LUMO energy levels of the VH-MON were simulated at −5.1 and −2.4 eV, respectively, by density functional theory (DFT) calculation. The VH-MON/TiO2–Pt composite exhibited promising activity and enhanced stability as a photocatalytic system for visible light-induced hydrogen production from water.

We report, for the first time, the synthesis of the Y3Al5O12:Ce3+ hollow phosphor particles with a uniform size distribution via the Kirkendall effect, characterized by using a combination of in situ X-ray diffraction and high-resolution transmission electron microscopy analyses as a function of calcination temperature. The formation of hollow Y3Al5O12:Ce3+ particles was revealed to originate from the different diffusivities of atoms (Al and Y) in a diffusion couple, causing a supersaturation of lattice vacancies. The optical characterization using photoluminescence spectroscopy and scanning confocal microscopy clearly showed the evidence of YAG (yttrium aluminum garnet) hollow shells with emission at 545 nm. Another advantage of this methodology is that the size of hollow shells can be tunable by changing the size of initial nanotemplates that are spherical aluminum hydroxide nanoparticles. In this study, we synthesized the hollow shell particles with average diameters of 140 and 600 nm as representatives to show the range of particle sizes. Because of the unique structural and optical properties, the Y3Al5O12:Ce3+ hollow shells can be another alternative to luminescence materials such as quantum dots and organic dyes, which promote their utilization in various fields, including optoelectronic and nanobio devices.Keywords: hollow spheres; Kirkendall effect; luminescence; monodisperse; phosphor nanoparticles; YAG;

We report on the fabrication of PbS/CH3NH3PbI3 (=MAP) core/shell quantum dot (QD)-sensitized inorganic–organic heterojunction solar cells on top of mesoporous (mp) TiO2 electrodes with hole transporting polymers (P3HT and PEDOT:PSS). The PbS/MAP core/shell QDs were in situ-deposited by a modified successive ionic layer adsorption and reaction (SILAR) process using PbI2 and Na2S solutions with repeated spin-coating and subsequent dipping into CH3NH3I (=MAI) solution in the final stage. The resulting device showed much higher efficiency as compared to PbS QD-sensitized solar cells without a MAP shell layer, reaching an overall efficiency of 3.2% under simulated solar illumination (AM1.5, 100 mW·cm–2). From the measurement of the impedance spectroscopy and the time-resolved photoluminescence (PL) decay, the significantly enhanced performance is mainly attributed to both reduced charge recombination and better charge extraction by MAP shell layer. In addition, we demonstrate that the MAP shell effectively prevented the photocorrosion of PbS, resulting in highly improved stability in the cell efficiency with time. Therefore, our approach provides method for developing high performance QD-sensitized solar cells.Keywords: CH3NH3PbI3; PbS quantum dots; photovoltaic; quantum dot-sensitized solar cell; spin-assisted successive ionic layer adsorption and reaction (spin-SILAR);

Organic photovoltaic devices are difficult to commercialize because of their vulnerability to chemical degradation related with oxygen and water and to physical degradation with aging at high temperatures. We investigated the photophysical degradation behaviors of a series of poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl C61-butyric acid methyl ester (PC60BM) bulk heterojunctions (BHJs) as a model system according to the donor–acceptor ratio. We found that the optimum P3HT:PC60BM ratio in terms of long-term stability differs from that in terms of initial cell efficiency. On the basis of cell performance decays and time-resolved photoluminescence measurements, we investigated the effects of oxygen and material self-aggregation on the stability of an organic photovoltaic device. We also observed the changes in morphological geometry and analyzed the surface elements to verify the mechanisms of degradation.Keywords: bulk heterojunction; degradation; lifetime; morphology; organic solar cells; stability;

Novel iridium(III) complexes containing bis(N-heterocyclic carbene), bis(imidazoline thione) L2, and bis(imidazoline selone) L3 were prepared. The iridium complexes bearing L2 and L3 showed the significant absorption of visible light with maximum intensity at ∼460 nm. Bis(2-(2′-benzothienyl)pyridinato)iridium(III) complexes (Ir-6) with L3 showed excellent ability as a photosensitizer of visible light. Under blue LED irradiation with maximum emission at 460 nm, 0.25 mol % Ir-6 showed 94% conversion of benzylamine for 5 h at room temperature. Through mechanistic studies, it was suggested that the photoinduced oxidative coupling of benzylamine by Ir-6 follows a singlet oxygen pathway. The excellent performance of Ir-6 originated from the efficient visible light absorption at 460 nm and the enhanced triplet state due to the heavy-atom effect of L3. This work shows that bis(imidazoline thione) and bis(imidazoline selone) can be efficient ligands for tuning the optical properties of iridium(III) complexes.

We suggest a 2D-plot representation combined with life cycle greenhouse gas (GHG) emissions and life cycle cost for various energy conversion technologies. In general, life cycle assessment (LCA) not only analyzes at the use phase of a specific technology, but also covers widely related processes of before and after its use. We use life cycle GHG emissions and life cycle cost (LCC) to compare the energy conversion process for eight resources such as coal, natural gas, nuclear power, hydro power, geothermal power, wind power, solar thermal power, and solar photovoltaic (PV) power based on the reported LCA and LCC data. Among the eight sources, solar PV and nuclear power exhibit the highest and the lowest LCCs, respectively. On the other hand, coal and wind power locate the highest and the lowest life cycle GHG emissions. In addition, we used the 2D plot to show the life cycle performance of GHG emissions and LCCs simultaneously and realized a correlation that life cycle GHG emission is largely inversely proportional to the corresponding LCCs. It means that an expensive energy source with high LCC tends to have low life cycle GHG emissions, or is environmental friendly. For future study, we will measure the technological maturity of the energy sources to determine the direction of the specific technology development based on the 2D plot of LCCs versus life cycle GHG emissions.

To understand the role of the dye/oxide interface, a model system using a nanocrystalline SnO2 and 3-hexyl thiophene based MK-2 dye is proposed. A thin interfacial TiO2 blocking layer (IBL) is introduced in between SnO2 and MK-2 and its effects on photocurrent–voltage, electron transport-recombination, and density of states (DOS) are systematically investigated. Compared to the bare SnO2 film, the insertion of IBL leads to a 14-fold improvement in the power conversion efficiency (PCE) despite little change in the dye adsorption amount, which is due to the 7-fold and 2-fold increase in the photocurrent density and voltage, respectively. The charge collection efficiency is substantially improved from 38% to 96% mainly due to the increase in the electron lifetime. The IBL is also found to enhance the dye regeneration efficiency as confirmed by the 15-fold faster dye bleaching recovery dynamics. The recombination resistance increases and the DOS decreases after surface modification of SnO2, which is responsible for the doubly increased voltage. This study suggests that the interfacial layer between the oxide and the dye plays a crucial role in retarding recombination, improving charge collection efficiency, increasing diffusion length, accelerating dye regeneration and narrowing the density of states.

We synthesized single-crystalline Sn-based oxides for use as electron-transporting layers (ETLs) in perovskite solar cells (PSCs). The control of the Zn-to-Sn cation ratio (Zn/Sn = 0–2) in a fixed concentration of hydrazine solution leads to the formation of various types of Sn-based oxides, i.e., spherical SnO2 and Zn2SnO4 nanoparticles (NPs), SnO2 nanorods, and Zn2SnO4 nanocubes. In particular, a ratio of Zn/Sn = 1 results in nanocomposites of single-crystalline SnO2 nanorods and Zn2SnO4 nanocubes. This is related to the concentration of free hydrazine unreacted with Zn and Sn ions in the reaction solution, because the resulting OH− concentration affects the growth rate of intermediate phases such as ZnSn(OH)6, Zn(OH)42− and Sn(OH)62−. Additionally, we propose plausible pathways for the formation of Sn-based oxides in hydrazine solution. The Sn-based oxides are applied as ETLs and annealed at a low temperature below 150 °C in PSCs. The PSCs fabricated by using the nanocomposite ETLs consisting of single-crystalline SnO2 nanorods and Zn2SnO4 nanocubes exhibit superior device performance to TiO2-based PSCs due to their excellent charge collection ability and optical properties, achieving a power conversion efficiency of ≥17%.

Sn–porphyrin networks were engineered on the surface of a thin layer chromatography (TLC) plate via Sonogashira coupling of the Sn–porphyrin building block and 1,4-diiodobenzene. The Sn–porphyrin film showed a strong Soret band absorption at 422 nm, emission at 600–630 nm, and excellent sensing performance toward nitrophenols in water.

This work shows that microporous organic network (MON) chemistry can be successfully applied for the development of a visible light-induced hydrogen production system. A visible light harvesting MON (VH-MON) was prepared by the Knoevenagel condensation of tri(4-formylphenyl)amine with [1,1′-biphenyl]-4,4′-diacetonitrile. Scanning electron microscopy (SEM) showed a 1D rod morphology of the VH-MON. Analysis of a N2 sorption isotherm showed a 474 m2 g−1 surface area and microporosity. Solid phase 13C nuclear magnetic resonance (NMR) and infrared (IR) absorption spectroscopy, and elemental analysis support the expected network structure. The VH-MON showed visible light absorption in 400–530 nm and vivid emission at 542 nm. The HOMO and LUMO energy levels of the VH-MON were simulated at −5.1 and −2.4 eV, respectively, by density functional theory (DFT) calculation. The VH-MON/TiO2–Pt composite exhibited promising activity and enhanced stability as a photocatalytic system for visible light-induced hydrogen production from water.