Ionic Ir(III) complex-interfacial layer for efficient carrier collection via induced electric dipole.

The power conversion efficiency (PCE) of polymer solar cells (PSCs) has recently reached >19% through the development of photoactive materials, particularly non-fullerene acceptors. Interfacial layers (ILs) have been another essential factor in optimizing device charge extraction. In this study, we propose a series of ILs, in which ionic iridium(III) (Ir(III)) complexes of different alkali metal cations (Li+, Na+, and K+) enhance the charge collection efficiency between zinc oxide and active layers through an induced internal electric field. The anionic coordinate sphere and counter-cations of the Ir(III) complexes are distributed according to the operating voltage of the PSCs, causing electric dipoles that enhance the internal electric field and charge collection efficiency. Ion species migration in the ILs is confirmed using electrochemical impedance spectroscopy. The PCE of the PM6:Y6-based PSCs was improved from 14.0% to 15.6% by introducing an IL (Ir-K+). Furthermore, the stability of PSCs containing ionic Ir(III) complexes is enhanced significantly under ultraviolet (UV) light and AM 1.5 G one-sun irradiation owing to the intense UV absorption capacity and photo durability of the ILs. A device containing the Ir(III) complex-based ILs retained ∼60% of its initial PCE after UV irradiation, whereas the control device retained only ∼20%.

Occupational exposure to VOCs and carbonyl compounds in beauty salons and health risks associated with it in South Korea.

Long-term exposure to volatile organic compounds (VOCs) and carbonyl compounds in beauty products may adversely impact the health of beauty salon technicians. Previous studies have focused on assessing indoor air concentrations of chemicals, such as benzene and toluene, and not on personal exposure concentrations. This study measured the indoor and personal exposure concentrations of VOCs and carbonyl compounds in fifty-three beauty salons in Korea. Non-carcinogenic and carcinogenic risks and sensitivity were analyzed using the Monte Carlo simulation technique. The indoor and personal exposure concentrations of acetone were 82.24 µg/m3 and 104.97 µg/m3, respectively, the highest among all measured chemicals. Beauty salon technicians who experienced adverse health effects had significantly higher concentrations of acetone, benzaldehyde, and toluene than those who did not experience adverse health effects (p-value < 0.05). The average hazard quotients of formaldehyde and acetaldehyde were higher than the acceptable risk level (1), and the average cancer risks of formaldehyde exceeded the acceptable risk level (10-6). Wearing personal protective equipment was the most efficient risk reduction strategy for reducing the non-cancer risks of acetaldehyde and formaldehyde and the carcinogenic risks of formaldehyde. The results of this study can be used as a basis for reducing exposure to VOCs and carbonyl compounds among salon technicians.

Effects of Legal Regulation on Indoor Air Quality in Facilities for Sensitive Populations - A Field Study in Seoul, Korea.

Facilities for sensitive populations have increased in Korea; and its indoor air quality (IAQ) was strictly regulated by the Korean government compared to other facilities. However, merely public facilities on certain level of total floor area were lawfully regulated. This study aims to characterize the indoor environment at facilities for sensitive populations in Korea and investigate the effects of legal regulation on IAQ throughout the duration of 1 year. Sixty facilities for sensitive populations were investigated. Particulate matter (PM10), nitrogen dioxide (NO2), carbon dioxide (CO2), carbon monoxide (CO), total bacteria count (TBC), total volatile organic compound (TVOC), formaldehyde (HCHO), radon (Rn), ozone (O3), asbestos, fine particulate matter (PM2.5), and volatile organic compounds (VOCs) were target pollutants. As a result, none of the rooms' concentration of CO, NO2, O3, Rn, asbestos, and VOCs exceeded the Korean Standard of Indoor Air Quality, while some rooms' concentration of other pollutants exceeded the KSIAQ. Statutory facilities had lower indoor pollutant concentrations and exceedance rates due to efficient ventilation system and the lack of kitchen location within the building, as opposed to non-statutory facilities. In addition, the VOCs had significant differences depending on the number of years it took for the building to be constructed. To reduce the indoor pollutants concentrations, efficient ventilation systems should be installed while controlling the main sources of pollutants. In addition, construction and remodeling using eco-friendly materials should be considered. The standards of IAQ for small size facilities should be included in the KSIAQ in the future.

Dopant-Free All-Back-Contact Si Nanohole Solar Cells Using MoOx and LiF Films.

We demonstrate novel all-back-contact Si nanohole solar cells via the simple direct deposition of molybdenum oxide (MoOx) and lithium fluoride (LiF) thin films as dopant-free and selective carrier contacts (SCCs). This approach is in contrast to conventionally used high-temperature thermal doping processes, which require multistep patterning processes to produce diffusion masks. Both MoOx and LiF thin films are inserted between the Si absorber and Al electrodes interdigitatedly at the rear cell surfaces, facilitating effective carrier collection at the MoOx/Si interface and suppressed recombination at the Si and LiF/Al electrode interface. With optimized MoOx and LiF film thickness as well as the all-back-contact design, our 1 cm(2) Si nanohole solar cells exhibit a power conversion efficiency of up to 15.4%, with an open-circuit voltage of 561 mV and a fill factor of 74.6%. In particular, because of the significant reduction in Auger/surface recombination as well as the excellent Si-nanohole light absorption, our solar cells exhibit an external quantum efficiency of 83.4% for short-wavelength light (∼400 nm), resulting in a dramatic improvement (54.6%) in the short-circuit current density (36.8 mA/cm(2)) compared to that of a planar cell (23.8 mA/cm(2)). Hence, our all-back-contact design using MoOx and LiF films formed by a simple deposition process presents a unique opportunity to develop highly efficient and low-cost nanostructured Si solar cells.

Highly efficient hybrid thin-film solar cells using a solution-processed hole-blocking layer.

We report the origin of the improvement of the power conversion efficiency (PCE) of hybrid thin-film solar cells when a soluble C(60) derivative, [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM), is introduced as a hole-blocking layer. The PCBM layer could establish better interfacial contact by decreasing the reverse dark-saturation current density, resulting in a decrease in the probability of carrier recombination. The PCE of this optimized device reached a maximum value of 8.34% and is the highest yet reported for hybrid thin-film solar cells.

N,N-(diphenylamino)fluorenylstyrene derivatives with the various heteroatom-containing moieties for blue organic light-emitting diodes.

A series of blue fluorescent materials 1-6 based on N, N-diphenyl aminofluorene styryl derivatives with six heteroatoms (PhOPh, PhSPh, PhSePh, PhPPh2, thiophene and dibenzothiophene), were synthesized and multilayer devices were fabricated. Interestingly, the EL efficiencies were very sensitive to the structural features of dopants in the emitting layers. Particularly, by using 1 as a dopant in emitting layer, a high-efficiency blue OLED was fabricated, showing the maximum luminance of 10420 cd/m2 at 11 V, the luminous efficiency of 8.6 cd/A at 20 mA/cm2, the power efficiency of 3.4 Im/W at 20 mA/cm2 and had a blue color with the CIE coordinates of (0.147, 0.156) at 8.0 V.

Visualizing indoor ozone exposures via o-dianisidine based colorimetric passive sampler.

In this study, we developed a colorimetric ozone passive sampler (OPS) incorporating o-dianisidine, a redox dye, into a polydimethylsiloxane sheet. The reaction between ozone (O3) and o-dianisidine result in a visible yellowish color change. Unlike previous passive methods that rely on nitrate extraction or the color disappearance of indigotrisulfonate, the OPS offered improved recognition of average O3 exposure. To optimize OPS based on time-weighted average (TWA), we extracted and quantified the amount of reacted o-dianisidine after exposing OPS to O3 by varying concentrations (0-200 ppb) within 8 h. Colorimetric changes of OPS were further analyzed by capturing images, and the effective absorbance of blue scale showed the best fit (EAB, R2 =0.997). OPS validation on visual detection assessed by six parameters: limit of detection, limit of quantification, reproducibility, sampling rate, selectivity to interfering gases, and sensitivity to environmental factors. To enhance visibility, the OPS was assembled with coloration exposure guidelines, and a smartphone app was developed to quantify average O3 exposures. We further conducted field tests that showed the significant disparity between O3 concentrations and personal O3 exposures, which is considered more crucial for assessing health risks. The OPS was optimized to monitor O3 exposure levels and raise awareness among workers and occupants regarding invisible indoor hazards.

Non-Fullerene Acceptors with Benzodithiophene-Based Fused Planar Ring Cores for Organic Solar Cells.

Fused aromatic rings are widely employed in organic solar cell (OSC) materials due to their planarity and rigidity. Here, we designed and synthesized four two-dimensional non-fullerene acceptors, D6-4F, D6-4Cl, DTT-4F, and DTT-4Cl, based on two new fused planar ring structures of f-DTBDT-C6 and f-DTTBDT. Owing to the desirable phase separation formed in the blend films and the higher energy levels induced by the extra alkyl groups, PM6:D6-4F-based devices achieved a high VOC = 0.91 V with PCE = 11.10%, FF = 68.54%, and JSC = 17.75 mA/cm2. Because of the longer π-conjugation of the f-DTTBDT core with nine fused rings, DTT-4F and DTT-4Cl showed high molar extinction coefficients and broad absorption bands that enhanced the current density of OSCs. Finally, the PM6:DTT-4F-based devices achieved a JSC = 19.82 mA/cm2 with PCE = 9.68%, VOC = 0.83 V, and FF = 58.85%.

Efficient deep-blue organic light-emitting diodes using double-emitting layer.

Efficient deep-blue organic light-emitting diodes were demonstrated using 1,4-tetranaphthalene doped in double-emitting layers (D-EMLs) consisting of 2-methyl-9,10-di(2-naphthyl)anthracene and 4'-(dinaphthalen-2-yl)-1,1'-binaphthyl as blue hosts. The device with D-EML exhibits good confinement of holes and electrons, as well as a broad recombination zone. The optimized device showed a peak current efficiency of 3.67 cd/A, a peak external quantum efficiency of 3.97%, and Commission Internationale de L'Eclairage coordinates of (0.16, 0.10).

White organic light-emitting diodes for emotion solid-state lighting.

The authors have demonstrated white organic light-emitting diodes for emotion solid-state lighting (ESSL) by using hole modulating layer (HML), N,N'-diphenyl-N,N'-bis-[4-(phenyl-m-tolyl-amino)-phenyl]-biphenyl-4,4'-diamine and N,N'-bis-(1-naphyl)-N,N'-diphenyl-1,1'-biphenyl-4, 4'-diamine, and mixed spacer (MS), 4,4',4"-tris(N-carbazolyl)-triphenylamine and {9,9-dimethyl-7-[10-(naphthalen-2-yl)anthracen-9-yl]-9H-fluoren-2-yl}triphenylsilane, respectively. The HML and MS were used for unbalance of holes and electrons. The ESSL showed various white light chromaticities of Commission Internationale de l'Eclairage coordinates from (0.46,0.42) as warm white emission to (0.29, 0.36) as cold white emission.

Efficient phosphorescent white organic light-emitting diodes using Ir(4-Me-2,3-dpq)2(przl-C6H4F) as a red emitter.

We demonstrated white organic light-emitting diodes (WOLED) using the iridium bis(4-methyl-2,3-phenylquinolinato-N,C2) fluorophenylpyrazolonate complex (Ir(4-Me-2,3-dpq)2(przl-C6H4F)) as a phosphorescent red dopant and iridium bis[(4,6-difluorophenyl)-pyridinato-N,C2] picolinate (Flrpic) as a phosphorescent blue dopant. The WOLED with Ir(4-Me-2,3-dpq)2(przl-C6H4F) had better exciton confinement in emitting layer and indicated smaller movement of exciton than the WOLED with iridium bis(2-phenylquinoline) acetylacetonate (Ir(2-pq)2(acac)) as phosphorescent red dopant. The optimized WOLED had a peak external quantum efficiency of 7.16%, current efficiency of 11.84 cd/A, and Commission Internationale de l'Eclairage (CIE(x,y)) coordinates of (0.35, 0.32). The WOLED also exhibited the minimal change with delta CIE(x,y) coordinates of +/- (0.01, 0.00) from 100 to 4000 cd/m2.

Efficient organic photovoltaic devices by using PEDOT:PSSs with excellent hole extraction ability.

We have demonstrated the poly(3-hexyl-thiophene-1,5-diyl) (P3HT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM) bulk heterojunction (BHJ) organic photovoltaic (OPV) devices on various poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSSs). The device with PEDOT:PSS of PH 500 adding 1% dimethyl sulfoxide (DMSO) showed the best performances in term of the fill factor and power conversion efficiency (PCE) than others. The hole extraction ability of PEDOT:PSS is very important to balance between holes and electrons mobility because the carrier mobility of PCBM (approximately 10(-4) cm2/Vs) is higher than that of P3HT (approximately 10(-6) cm2/Vs) in P3HT:PCBM BHJ structure. The optimized BHJ OPV with PEDOT:PSS of PH 500 adding 1% DMSO showed a short-circuit current density of 8.92 mA/cm2 and a PCE of 2.97%, which was nearly increased to 2.5 times than that of control device with PEDOT:PSS of P VP Al 4083.

Efficient deep-blue organic light-emitting diodes with a 1,4-(dinaphthalen-2-yl)-naphthalene.

Deep-blue organic light-emitting diodes (OLEDs) with nearly 5% external quantum efficiency were demonstrated using a 1,4-(dinaphthalen-2-yl)-naphthalene (DNN) host. The 4,4'-bis(9-ethyl-3-carbazovinylene)-1,1'-biphenyl (BCzVBi) dopant that was used in this experiment effectively accepted energy from the DNN host via Förster energy transfer because the photoluminescence spectrum of the DNN host showed better spectra overlap with the ultraviolet-visible (UV-vis) absorption spectrum of the BCzVBi dopant than the photoluminescence spectrum of the 2-methyl-9,10-bis(naphthalen-2-yl)anthracene host did. Moreover, the DNN host had a higher energy bandgap (3.5 eV) than the BCzVBi dopant did (3.0 eV), while the MADN host had the same energy bandgap as the BCzVBi dopant. The optimized deep-blue device also had ETL of bis-(2-methyl-8-quinolinolate)-4-(phenylphenolato)aluminium which showed smoother sigma of 0.6 nm and higher Tg of 92 degrees than those of 4,7-diphenyl-1,10-phenanthroline (14.8 nm and 62 degrees C). The deep-blue device exhibited a peak current efficiency of 5.68 cd/A, a peak external quantum efficiency of 4.89%, and Commission Internationale d' Eclairage coordinates of (0.15, 0.13).

Bias stress effects on different dielectric surfaces of pentacene thin-film transistors.

In this paper, it was demonstrated that pentacene thin-film transistors (TFTs) were fabricated with an organic adhesion layer between an organic semiconductor and a gate insulator. In order to form polymeric film as an adhesion layer, a vapor deposition polymerization (VDP) process was introduced to substitute for the usual spin-coating process. Field effect mobility, threshold voltage, and on/off current ratio in pentacene TFTs with a 15 nm thick organic adhesion layer were about 0.4 cm2/Vs, -1 V, and 10(6), respectively. We also demonstrated that threshold voltage strongly depends on the stress time when a gate voltage has been applied for bias stress test. We suggest that a polyimide adhesion layer fabricated by the VDP method can be applied to realize organic TFTs with long-term stability because of lower threshold voltage shifts due to reduced charge trapping at the interface between the pentacene semiconductor and the polyimide layer.

Highly efficient blue light-emitting diodes based on diarylanthracene/triphenylsilane compounds.

New host materials have been designed and synthesized, (4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)triphenylsilane (ANPTPS) and (9,9-dimethyl-7-(10-(naphthalen-2-yl)anthracen-9-yl)-9H-fluoren-2-yl)triphenylsilane (ANFTPS), and photophysical characteristics investigated to determine suitability as candidates for blue light-emitting materials. To explore the electroluminescent properties, multilayered OLEDs were fabricated with the device structure of ITO/NPB/Host (ANPTPS and ANFTPS): 8% Dopant (PFVtPh and PCVtPh)/Bphen/Liq/Al. By using a host (ANPTPS) and a dopant (PFVtPh) as the emitting layer, high-efficiency blue OLEDs were fabricated with a maximum luminance of 3991 cd/cm2 at 8.0 V, a luminous efficiency of 5.99 cd/A at 20 mA/cm2, a power efficiency of 3.11 lm/W at 20 mA/cm2, an external quantum efficiency of 4.13% at 20 mA/cm2, and CIEx, y coordinates of (x = 0.15, y = 0.18) at 8.0 V.

High efficiency phosphorescent blue organic light-emitting diodes using double emitting layer.

We have demonstrated a highly efficient blue phosphorescent organic light emitting diodes (PHOLED) using iridium (111) bis[(4,6-di-fluoropheny)-pyridinato-N,C2] picolinate doped in double emitting layers (D-EML), N,N-dicarbazolyl-3,5-benzene (mCP) and p-bis (triphenylsilyly)benzene (UGH2). D-EML layers were employed to broaden the exciton formation zone and confine excitons. The optimized blue PHOLEDs having mCP/UGH2 as D-EML with a thickness of 200/100 A, exhibited a peak external quantum efficiency of 11.44%, power efficiency of 16.8 Im/W, luminous efficiency of 23.14 cd/A, and Commission Internationale de l'Eclairage coordinates of (0.17, 0.33).

Modified DCM-type materials for red fluorescent organic light-emitting diodes.

A series of red emitters 1-3 based on modified DCM were synthesized and their electroluminescent properties were investigated. A device employing red emitter 2 as a dopant exhibited efficient red emission with maximum luminous efficiency of 1.87 cd/A, maximum power efficiency of 0.78 lm/W, maximum external quantum efficiency of 1.52%, and CIE coordinates of (0.65, 0.35) at 7.0 V.

Highly efficient blue fluorescent materials based on fluorene derivatives end-capped with arylaminofluorenylethylenes for organic light-emitting diodes.

Multilayered organic light-emitting diodes (OLEDs) were fabricated by using the new fluorine derivatives end-capped with arylaminofluorenylethylenes as dopant materials. The device structure was ITO/NPB/15% blue dopants doped in MADN/Bphen/Liq/Al. Among those, a device shows the maximum luminance of 40800 cd/m2 at 12 V, the luminous efficiency of 12.8 cd/A at 20 mA/cm2, power efficiency of 9.13 Im/W at 20 mA/cm2 and CIE(x,y) coordinates of (x = 0.188, y = 0.372) at 8 V.

Prediction Model for Airborne Microorganisms Using Particle Number Concentration as Surrogate Markers in Hospital Environment.

Indoor microbiological air quality, including airborne bacteria and fungi, is associated with hospital-acquired infections (HAIs) and emerging as an environmental issue in hospital environment. Many studies have been carried out based on culture-based methods to evaluate bioaerosol level. However, conventional biomonitoring requires laborious process and specialists, and cannot provide data quickly. In order to assess the concentration of bioaerosol in real-time, particles were subdivided according to the aerodynamic diameter for surrogate measurement. Particle number concentration (PNC) and meteorological conditions selected by analyzing the correlation with bioaerosol were included in the prediction model, and the forecast accuracy of each model was evaluated by the mean absolute percentage error (MAPE). The prediction model for airborne bacteria demonstrated highly accurate prediction (R2 = 0.804, MAPE = 8.5%) from PNC1-3, PNC3-5, and PNC5-10 as independent variables. Meanwhile, the fungal prediction model showed reasonable, but weak, prediction results (R2 = 0.489, MAPE = 42.5%) with PNC3-5, PNC5-10, PNC > 10, and relative humidity. As a result of external verification, even when the model was applied in a similar hospital environment, the bioaerosol concentration could be sufficiently predicted. The prediction model constructed in this study can be used as a pre-assessment method for monitoring microbial contamination in indoor environments.

A spacer effect on electroluminescent characteristics of white organic light-emitting diodes.

The authors have demonstrated efficient and color-stable white organic light-emitting diodes (WOLEDs) by using three emitters, 4"-(2,2-diphenylvinyl)-1-[4-(N,N-diphenylamino)-styryl]-terphenyl (PVAS-tPh), fac tris(2-phenypyridine) irdium(III) (Ir(ppy)3), and Bis(5-benzoyl-2-phenylpyridinato-C,N)iridium(III) (acetylacetonate) (Bzppy)2Ir(III)acac). In this WOLEDs, 4,4'-N, N'-dicarbazole-biphenyl (CBP) were used as a spacer among three emitting layers. CBP between red and green emitting layers prevented the Commission Internationale de L'Eclairage (CIE(x,y)) coordinates change of white emission. As a result, WOLEDs showed a minimal change of deltaCIE(x,y) < (0.01,0.02) for the brightness change form 100 to 20 000 cd/m2.