Optical upconversion via sensitized triplet–triplet exciton annihilation converts incoherent low-energy photons to shorter wavelengths under modest excitation intensities1,2,3. Here, we report a ...solid-state thin film for infrared-to-visible upconversion that employs lead sulphide colloidal nanocrystals as a sensitizer. Upconversion is achieved from pump wavelengths beyond λ = 1 μm to emission at λ = 612 nm. When excited at λ = 808 nm, two excitons in the sensitizer are converted to one higher-energy state in the emitter at a yield of 1.2 ± 0.2%. Peak efficiency is attained at an absorbed intensity equivalent to less than one sun. We demonstrate that colloidal nanocrystals are an attractive alternative to existing molecular sensitizers, given their small exchange splitting, wide wavelength tunability, broadband infrared absorption, and our transient observations of efficient energy transfer. This solid-state architecture for upconversion may prove useful for enhancing the capabilities of solar cells and photodetectors.
M. Shtein and co‐workers use guard flow‐enhanced organic vapor jet printing for the additive patterning of pentacene thin fifilms in air, and perform in situ X‐ray diffraction to relate process ...variables, oxidation, structural defects, and electronic properties in thin‐film transistor applications. The process structureproperty relationship is quantifified, and the field‐effect mobility is extrapolated based on the processing conditions. The schematic shown represents the GF‐OVJP process with in situ diffraction and contacts for TFT measurements.
To accelerate the pace of materials discovery and application, comprehensive links need to be established between a material's structure, properties, and process conditions used to obtain the ...material and/or final application format. This work examines the dry printing of pentacene thin film transistor (TFT) channels by guard flow‐enhanced organic vapor jet printing (GF‐OVJP), a technique that enables direct, solvent‐free, additive patterning of device‐quality molecular semiconductors in air. Deposition in air entails non‐trivial effects at the boundary between ambient surroundings and the gas jet carrying the semiconductor vapor that influence the morphology and properties of the resulting electronic devices. Synchrotron X‐ray diffraction is employed, complemented by measurement of electronic properties of GF‐OVJP deposited films in a TFT to reveal how the morphology and electronic properties of the films depend on thickness, location within the printed pattern, nozzle translation velocity, and other process parameters. The hole field‐effect mobility of the printed pentacene film is linked quantitatively with its crystallinity, as well as with extent of exposure to ambient air during deposition. The analysis can be extended to accurately predict the performance of devices deposited in air by GF‐OVJP, which are demonstrated here for a planar, large area deposit.
Guard flow‐enhanced organic vapor jet printing technique enables additive patterning of organic thin films in air, without the use of solvents. During deposition in air, ambient oxygen and moisture are incorporated in the film's “wing” region. This work relates the degree of air exposure to pentacene film's morphology and electronic properties via synchrotron X‐ray diffraction and thin‐film transistor measurements, respectively.
We present a novel method to model and estimate elastic geometric deformations of an observed object, whether they are caused by the object's own dynamic behavior, or by the dynamic behavior of the ...imaging device, or both. A procedure for estimating the space of possible deformations the object may undergo based only on a set of observations is derived. This information is then employed to derive a linear estimator of the elastic deformation in any given observation. Application to change detection is presented.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages ...111-129).
Recent trends in renewable energy made silicon based photovoltaics the undisputed leader. Therefore, technologies that enhance, instead of compete with, silicon based solar cells are desirable. One such technology is the use of organic semiconductors and noncrystalline semiconductors for photon up- and down-conversion. However, the understanding of energy transfer in these hybrid systems required to effectively engineer devices is missing. In this thesis, I explore and explain the mechanism of energy transfer between noncrystalline semiconductors and organic semiconductors. Using a combination of density functional calculations, molecular dynamics, and kinetic theory, I have explored the geometry, morphology, electronic structure, and coarse grained kinetics of these system. The result is improved understanding of the transfer mechanism, rate, and the device structure needed for efficient devices. I have also looked at machine learning inspired algorithm for acceleration of density functional theory methods. By training machine learning models on DFT data, a much improved initial guess can be made, greatly accelerating DFT optimizations. Generating and examining this data set also revealed a remarkable degree of structure, that perhaps can be further exploited in the future.
by Nadav Geva.
Ph. D.
By harvesting sub-bandgap photons, we have a path to overcome the Shockley-Queisser limit in photovoltaics (PVs). We investigate semiconductor nanocrystal (NC) sensitized upconversion via ...triplet-triplet annihilation (TTA) in organic semiconductors (OSCs). Since this process relies on optically inactive triplet states in the OSCs, we utilize PbS NCs to directly sensitize the triplet state via energy transfer. This is possible due to the strong spin-orbit coupling in PbS NCs, resulting in rapid spin-dephasing of the exciton. Current technology allows for upconversion of light with a photon energy above \sim 1.1 eV. However, while internal efficiencies are rapidly improving, the low external device efficiencies render them impractical for applications, as devices are based on a single monolayer of NCs. Our results show simply increasing the PbS NC film thickness does not show improvement in the efficiency due to poor exciton transport between PbS NCs. Here, we present a new strategy to increase the external upconversion efficiency by utilizing thin tinbased halide perovskites as the absorbing layer. Resonant energy transfer from the perovskite to the PbS NCs allows for subsequent sensitization of the triplet state in rubrene.
Semiconductor nanocrystals are a promising class of materials for a variety of novel optoelectronic devices, since many of their properties, such as the electronic gap and conductivity, can be ...controlled. Much of this control is achieved via the organic ligand shell, through control of the size of the nanocrystal and the distance to other objects. We here simulate ligand-coated CdSe nanocrystals using atomistic molecular dynamics, allowing for the resolution of novel structural details about the ligand shell. We show that the ligands on the surface can lie flat to form a highly anisotropic 'wet hair' layer as opposed to the 'spiky ball' appearance typically considered. We discuss how this can give rise to a dot-to-dot packing distance of one ligand length since the thickness of the ligand shell is reduced to approximately one-half of the ligand length for the system sizes considered here; these distances imply that energy and charge transfer rates between dots and nearby objects will be enhanced due to the thinner than expected ligand shell. Our model predicts a non-linear scaling of ligand shell thickness as the ligands transition from 'spiky' to 'wet hair'. We verify this scaling using TEM on a PbS nanoarray, confirming that this theory gives a qualitatively correct picture of the ligand shell thickness of colloidal quantum dots.
Background
Visceral peritoneal colorectal metastases (VPCMs) may further metastasize to lymph nodes that drain those organs. The rate of lymph node metastases (LNMs) from VPCMs and their clinical and ...prognostic significance are unknown.
Methods
This study retrospectively analyzed the authors’ institutional databases of 160 patients with peritoneal colorectal metastases who underwent cytoreductive surgery and hyperthermic intraperitoneal chemotherapy. Patients with LNM-VPCM (
n
= 12) were identified by pathologic reports, and both their short- and long-term outcomes were compared with those of patients without LNM-VPCM.
Results
The clinical presentation and primary tumor pathologic characteristics did not differ between the two groups. The patients with LNM-VPCM had a higher tumor burden (measured by the peritoneal carcinomatosis index PCI) and visible remnant disease compared with those who had no LNM-VPI (10 vs 5.5
p
= 0.03 vs 33.3% vs 6.8%
p
= 0.007, respectively). The postoperative outcomes also were comparable. The patients with LNM-VPCM had a shorter overall survival (OS) than those without LNM-VPCM (median OS, 22.5 months; 95% confidence interval CI, 15.1–29.9 months vs 40.1 months; 95% CI, 38.1–42 months;
p
= 0.02). However, only tumor grade and PCI were predictors of OS in the multivariate analysis (hazard ratio HR, 2.33
p
= 0.001; 1.77
p
= 0.03, respectively). The study showed that LNM-VPCM was associated with systemic but not peritoneal recurrence compared with non-LNM-VPCM (81.8% vs 51.6% for systemic recurrence, respectively;
p
= 0.05).
Conclusion
The small distinct group of patients defined by LNM-VPCM were prone to systemic recurrence. Given its correlation with systemic recurrence, LNM-VPCM may indicate the need for adjuvant treatment.
ObjectivesTo review the characteristics and motivations of patients seeking second opinions, and the impact of such opinions on patient management, satisfaction and cost effectiveness.Data ...sourcesEmbase, Medline, PsycINFO and Health Management Information Consortium (HMIC) databases.Study designA systematic literature search was performed for terms related to second opinion and patient characteristics. Study quality was assessed using the National Institutes of Health Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies.Data collection/extraction methodsWe included articles focused on patient-initiated second opinions, which provided quantitative data on their impact on diagnosis, treatment, prognosis or patient satisfaction, described the characteristics or motivating factors of patients who initiated a second opinion, or the cost-effectiveness of patient-initiated second opinions.Principal findingsThirty-three articles were included in the review. 29 studies considered patient characteristics, 19 patient motivating factors, 10 patient satisfaction and 17 clinical agreement between the first and second opinion. Seeking a second opinion was more common in women, middle-age patients, more educated patients; and in people having a chronic condition, with higher income or socioeconomic status or living in central urban areas. Patients seeking a second opinion sought to gain more information or reassurance about their diagnosis or treatment. While many second opinions confirm the original diagnosis or treatment, discrepancies in opinions had a potential major impact on patient outcomes in up to 58% of cases. No studies reported on the cost effectiveness of patient initiated second opinions.ConclusionsThis review identified several demographic factors associated with seeking a second opinion, including age, gender, health status, and socioeconomic status. Differences in opinion received, and in the impact of change in opinion, varies significantly between medical specialties. More research is needed to understand the cost effectiveness of second opinions and identify patient groups most likely to benefit from second opinions.
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