It has been generally believed and assumed that organometal halide perovskites would form type II P–N junctions with fullerene derivatives (C60 or PCBM), and the P–N junctions would provide driving ...force for exciton dissociation in perovskite‐based solar cell. To the best of our knowledge, there is so far no experiment proof on this assumption. On the other hand, whether photogenerated excitons can intrinsically dissociate into free carrier in the perovskite without any assistance from a P–N junction is still controversial. To address these, the interfacial electronic structures of a vacuum‐deposited perovskite/C60 and a solution‐processed perovskite/PCBM junctions is directly measured by ultraviolet photoelectron spectroscopy. Contrary to the common believes, both junctions are found to be type I N–N junctions with band gap of the perovskites embedded by that of the fullerenes. Meanwhile, device with such a charge inert junction can still effectively functions as a solar cell. These results give direct experimental evidence that excitons are dissociated to free carriers in the perovskite film even without any assistance from a P–N junction.
While perovskites/fullerene is commonly assumed to form a type II P–N junction with its internal E‐field facilitating exciton dissociation, it is found that perovskite/C60 (PCBM) is a charge inert type I N–N junction. Devices with such a junction show photovoltaic effects effectively, thus photogenerated excitons can indeed dissociate to free carriers in the perovskite film.
High-performance deep-blue emitting phenanthroimidazole derivatives with a structure of donor–linker–acceptor were designed and synthesized. By using different linkers and different linking ...positions, four deep-blue emitters were obtained and used as emitters or bifunctional hole-transporting emitters in OLEDs. Such devices show low turn-on voltages (as low as 2.8 V), high efficiency (2.63 cd/A, 2.53 lm/W, 3.08%), little efficiency roll-off at high current densities, and stable deep-blue emissions with CIE y < 0.10. Performances are among the best comparing to recently reported deep-blue emitting devices with similar structures. The results suggest that the combination of the phenanthroimidazole and the donor–linker–acceptor structure can be an important approach for developing high performance deep-blue emitters in particular for lighting applications.
High performance organic photovoltaic devices typically rely on type‐II P/N junctions for assisting exciton dissociation. Heremans and co‐workers recently reported a high efficiency device with a ...third organic layer which is spatially separated from the active P/N junction; but still contributes to the carrier generation by passing its energy to the P/N junction via a long‐range exciton energy transfer mechanism. In this study the authors show that there is an additional mechanism contributing to the high efficiency. Some bipolar materials (e.g., subnaphthalocyanine chloride (SubNc) and subphthalocyanine chloride (SubPc)) are observed to generate free carriers much more effectively than typical organic semiconductors upon photoexcitation. Single‐layer devices with SubNc or SubPc sandwiched between two electrodes can give power conversion efficiencies 30 times higher than those of reported single‐layer devices. In addition, internal quantum efficiencies (IQEs) of bilayer devices with opposite stacking sequences (i.e., SubNc/SubPc vs SubPc/SubNc) are found to be the sum of IQEs of single layer devices. These results confirm that SubNc and SubPc can directly generate free carriers upon photoexcitation without assistance from a P/N junction. These allow them to be stacked onto each other with reversible sequence or simply stacking onto another P/N junction and contribute to the photocarrier generation.
Subnaphthalocyanine chloride (SubNc) and subphthalocyanine chloride (SubPc) are identified as novel bipolar organic semiconductors with unusually high freecarrier generation upon photoexcitation. Functioning of devices with opposite stacking order (SubNc/SubPc vs SubPc/SubNc) confirms their operation does not rely on charge dissociation at the interfaces. These enable a new class of organic photovoltaic devices with non‐p–n‐junction‐based architectures.
The efficiency of a boron subphthalocyanine chloride/fullerene device is enhanced from 2.5% to 3.2% after inserting UV ozone treated ZnO (UV-ZnO) which is due to improved SubPc absorption by light ...scattering. Moreover, the UV-ZnO device shows <5% PCE drop while a standard device shows 35% drop because of the stable high work function of the UV-ZnO layer.
Improved PCE (from 2.5 to 3.2%) and stability of SubPc/C
60
-based OPV device using an UV-ozone treated ZnO anode buffer.
Organometal trihalide perovskite has recently emerged as a new class of promising material for high efficiency solar cells applications. While excess ions in perovskites are recently getting a great ...deal of attention, there is so far no clear understanding on both their formation and relating ions interaction to the photocharge generation in perovskite. Herein, we showed that tremendous ions indeed form during the initial stage of perovskite formation when the organic methylammonium halide (MAXa, Xa = Br and I) meets the inorganic PbXb 2 (Xb = Cl, Br, I). The strong charge exchanges between the Pb2+ cations and Xa‑ anions result in formation of ionic charge transfer complexes (iCTC). MAXa parties induce empty valence electronic states within the forbidden bandgap of PbXb 2. The strong surface dipole provide sufficient driving force for sub-bandgap electron transition with energy identical to the optical bandgap of forming perovskites. Evidences from XPS/UPS and photoluminescence studies showed that the light absorption, exciton dissociation, and photocharge generation of the perovskites are closely related to the strong ionic charge transfer interactions between Pb2+ and Xa‑ ions in the perovskite lattices. Our results shed light on mechanisms of light harvesting and subsequent free carrier generation in perovskites.
In article number 1606909, Ming‐Fai Lo, Chun‐Sing Lee, and co‐workers report unusual free‐carrier generation in some bipolar organic materials (SubNc and SubPc) upon photoexcitation. Single‐layer ...devices with SubNc or SubPc sandwiched between two electrodes can give power conversion efficiencies 30 times higher than previously reported single‐layer devices. Interestingly, these photoactive layers can be stacked onto each other with any sequence to generate a photocurrent in OPV devices.
Attendance at emergency departments and unplanned hospital readmissions are common for frail older patients after discharge from hospitals. A virtual ward service was piloted to deliver ..."hospital-at-home" services by community nurses and geriatricians to frail older patients immediately after their discharge from hospital to reduce emergency services utilization.
This study examined the impacts of the virtual ward service on changes in the patients' emergency attendance and medical readmissions, and their quality of life (QOL).
A matched-control quasi-experimental study was conducted at four hospitals, with three providing the virtual ward service (intervention) and one providing the usual community nursing care (control). Subjects in the intervention group were those who are at high risk of readmission and who are supported by home carers recruited from the three hospitals providing the virtual ward service. Matched control patients were those recruited from the hospital providing usual care. Outcome measures include emergency attendance and medical readmission in the past 90 days as identified from medical records, and patient-reported QOL as measured by the modified Quality-of-Life Concerns in the End of Life Questionnaire (Chinese version). Wilcoxon signed-rank tests compared the changes in the outcome variables between groups.
A total of 39 patients in each of the two groups were recruited. The virtual ward group showed a greater significant reduction in the number of unplanned emergency hospital readmissions (-1.41±1.23 versus -0.77±1.31; P=0.049) and a significant improvement in their overall QOL (n=18; 0.60±0.56 versus 0.07±0.56; P=0.02), but there was no significant difference in the number of emergency attendances (-1.51±1.25 versus -1.08±1.48; P=0.29).
The study results support the effectiveness of the virtual ward service in reducing unplanned emergency medical readmissions and in improving the QOL in frail older patients after discharge.
Our pilot study has demonstrated improvements in health outcomes through participation in a new sport, light volleyball (LVB), among older adults. In response to the promising results of the LVB ...pilot study and the priority of allocating resources to the prevention of age-related fitness degradation by the Hong Kong (HKG) government, the present study aims to investigate the effectiveness of a LVB intervention on physical and psychological health attributes among older adults at a larger scale in HKG.
This study will apply both quantitative and qualitative methods with a large sample (approximately 315 participants). We will adopt a randomized controlled trial (RCT) design to further evaluate the effectiveness of a LVB intervention on health outcomes against a comparison group, Tai Chi (TC), and a control group (C). Older adults will be eligible to join the intervention if they are (a) aged 65 years and above; (b) living in the community independently; (c) absent of diagnosed cognitive impairment; (d) not regular participants in a structured PA program for two years preceding the study; and (e) able to achieve a passing score on the Timed-up-and-go test (TUG) and Abbreviated Mental Test (AMT).About 315 participants will be randomly assigned into 3 groups in 1:1:1 ratio. LVB group participants will receive 16-week LVB program; TC group will utilize a simplified 24-form Yang Style TC, and C group participants will be instructed to maintain their normal daily activity and join regular non-exercise social gatherings. Measurements will be collected before and after the intervention, and 6 months and 12 months after completion of the intervention.
This intervention, if effective, will enhance older adult's physical and psychological health, and provide the data and evidence to support policymaking in relation to future PA promotion for older adults.
ChiCTR1900026657.
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•Solid-state DSSCs have reported performance lower than that of liquid-state.•Energy band structure of FTO/TiO2/N179/spiro-OMeTAD interface is studied.•Surface dipole is observed at ...N719/spiro-OMeTAD interface.•This results in electronic mismatch in hole-collection.
Fully solid-state dye-sensitized solar cell (DSSC) has attracted much recent attention. While the origins of the lower performance in DSSC using solid electrolyte are not fully understood, there is so far no report on their interfacial electronic structures. Here, we report the charge exchange and interfacial energetics in a standard solid-state DSSC with a structure of FTO/TiO2/cis-disothiocyanato-bis(2,2′-bipyridyl-4,4′-dicarboxylato) ruthenium(II) bis-(tetrabutylammonium) (N179 dye)/2,2,7,7-tetrakis-(N,N-di-pmethoxyphenyl-amine) 9,9-spirobifluorene (spiro-OMeTAD). While the electron-extracting barrier at TiO2/N719 interface is negligibly small (0.19eV); the abrupt vacuum levels (VLs) offsets at N719/spiro-OMeTAD interfaces results in large hole-extracting barrier of 0.43eV. Our results suggest an electronic mismatch in charge collection using spiro-OMeTAD as the hole-conducting material.
The defect state distribution for devices prepared with different idling time from BPhen to Mg:Ag deposition. Display omitted
•Idling time, a long ignored parameter is shown to influence OPV ...performance.•Metal atom penetration through BPhen decreases with increasing idling time.•These are attributed to the slow process of ‘self-reorganization’ of BPhen layer.
Deposition of metal cathode in organic photovoltaic (OPV) devices is known to cause serious metal atom penetration into the active layers and as a remedy, exciton blocking layer (EBL) is implemented. It is found that the metal penetration through EBL can be controlled by optimizing the idling time between the depositions of EBL and cathode layers. Both electrical and optical data show that the resistance of BPhen layer (EBL) to metal (Mg:Ag) penetration increase with increasing idling time. Also, significant variation in power conversion efficiency (PCE) is observed in subphthalocyanine chloride (SubPc)/fullerene (C60) based organic photovoltaic (OPV) cells by simply adding idling time as an additional control parameter. Device with optimized BPhen thickness and idling time resulted in a PCE of 2.8% whereas that of no idling time consideration has PCE limited at 2.3%. These observations are attributed to slow processes of self-organization in BPhen after their depositions.
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