| 1. |
- Cai, Xia, et al.
(author)
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Data-driven design of high-performance MASn(x)Pb(1-x)I(3) perovskite materials by machine learning and experimental realization
- 2022
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In: Light. - : Springer Nature. - 2095-5545 .- 2047-7538. ; 11:1
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Journal article (peer-reviewed)abstract
- The photovoltaic performance of perovskite solar cell is determined by multiple interrelated factors, such as perovskite compositions, electronic properties of each transport layer and fabrication parameters, which makes it rather challenging for optimization of device performances and discovery of underlying mechanisms. Here, we propose and realize a novel machine learning approach based on forward-reverse framework to establish the relationship between key parameters and photovoltaic performance in high-profile MASn(x)Pb(1-x)I(3) perovskite materials. The proposed method establishes the asymmetrically bowing relationship between band gap and Sn composition, which is precisely verified by our experiments. Based on the analysis of structural evolution and SHAP library, the rapid-change region and low-bandgap plateau region for small and large Sn composition are explained, respectively. By establishing the models for photovoltaic parameters of working photovoltaic devices, the deviation of short-circuit current and opencircuit voltage with band gap in defective-zone and low-bandgap-plateau regions from Shockley-Queisser theory is captured by our models, and the former is due to the deep-level traps formed by crystallographic distortion and the latter is due to the enhanced susceptibility by increased Sn (4+ )content. The more difficulty for hole extraction than electron is also concluded in the models and the prediction curve of power conversion efficiency is in a good agreement with Shockley-Queisser limit. With the help of search and optimization algorithms, an optimized Sn:Pb composition ratio near 0.6 is finally obtained for high-performance perovskite solar cells, then verified by our experiments. Our constructive method could also be applicable to other material optimization and efficient device development.
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| 2. |
- Carlegrim, Elin, et al.
(author)
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Characterization of the Ni/V(TCNE)x interface for hybrid spintronics applications
- 2010
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In: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 11:6, s. 1020-1024
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Journal article (peer-reviewed)abstract
- Vanadium tetracyanoethylene, V(TCNE)x, is an organic-based magnet with properties suitable for spintronics applications, e.g. spin valves. In this paper we propose a new hybrid organic spin valve design where V(TCNE)x is used as a spin-transporting and spin-filtering layer sandwiched between two ferromagnetic (FM) metal contacts, i.e. FM/V(TCNE)x/FM. As the spin injection and detection of such a device occurs at the interfaces the quality of those are of crucial importance. Therefore, the Ni/V(TCNE)x interface has been investigated by X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption spectroscopy (NEXAFS) as well as compared with XPS results from a model system, Ni/TCNE. Ni chemically interact with both the vinyl and cyano groups but there is no evidence for significant diffusion of Ni into the V(TCNE)x film. As the chemical interaction affects the spin injection and detection negatively by modifying the lowest unoccupied molecular orbital (LUMO) and destroying the magnetic ordering network at the surface, these results indicate that there is need for a buffer layer between V(TCNE)x and Ni, and in extension most likely between V(TCNE)x and any FM contact.
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| 3. |
- Carlegrim, Elin, et al.
(author)
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Electronic structure of thin film cobalt tetracyanoethylene, Co(TCNE)x
- 2010
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In: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 161:17-18, s. 1892-1897
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Journal article (peer-reviewed)abstract
- V(TCNE)x, TCNE=tetracyanoethylene, x~2, is a semiconducting organicbased magnet and one of very few organic-based magnets with critical temperature above room temperature (RT). With the aim to understand the key design criteria for achieving RT organic-based magnets we have started to study the electronic and chemical structure of members of the M(TCNE)x family with significantly lower critical temperatures than V(TCNE)x. In this paper, Co(TCNE)x, x~2, (Tc~44 K, derived from its powder form) were prepared by a method based on physical vapor deposition, resulting in oxygen-free thin films. The results propose Co(TCNE)x to contain to local bonding disorder in contrast to V(TCNE)x thin films, which can be grown virtually defect free. In addition, the Co L-edge does not show any pronounced fine structure, suggesting the crystal field to be very weak. By using a variety of photoemission and X-ray absorption techniques the highest occupied molecular orbital (HOMO) of Co(TCNE)x was determined to mainly be TCNE-derived while the states originating from Co(3d) are localized at higher binding energies. This is in stark contrast to V(TCNE)x where V(3d) is mainly responsible for the HOMO. As the HOMO of Fe(TCNE)x (Tc~121 K, derived from its powder form) is TCNE-derived these results show that Co(TCNE)x is more similar to Fe(TCNE)x than to V(TCNE)x in terms of electronic structure.
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| 4. |
- Chen, Ruoqing, et al.
(author)
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Marital status, telomere length and cardiovascular disease risk in a Swedish prospective cohort
- 2020
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In: Heart. - : BMJ Publishing Group Ltd. - 1355-6037 .- 1468-201X. ; 106:4, s. 267-272
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Journal article (peer-reviewed)abstract
- OBJECTIVE: To investigate if marital status is associated with risk of cardiovascular disease (CVD) and to explore the potential influence of leucocyte telomere length (LTL), a marker of biological ageing, on such association.DESIGN: Population-based prospective cohort study SETTINGS: Swedish Twin Registry.PARTICIPANTS: Based on the Screening Across the Lifespan Twin Study from the Swedish Twin Registry, we included 10 058 twins born between 1900 and 1958 who underwent an interview between 1998 and 2002 during which information about marital status was collected. Blood samples from these participants were subsequently collected between 2004 and 2008 and used for LTL assessment using quantitative PCR technique.MAIN OUTCOME MEASURES: Incident cases of CVD were identified through the Swedish Patient Register and Causes of Death Register through December 31, 2016. Multivariable linear regression and Cox proportional hazards regression models were used to estimate the regression coefficients (βs) and HRs with 95% CIs respectively. Potential confounders included age, sex, educational attainment and body mass index.RESULTS: A total of 2010 participants were diagnosed with CVD during a median follow-up of 9.8 years. LTL was shorter among individuals living singly, including those who were divorced or separated (β:-0.014, 95% CI: -0.035, 0.007), widowed (β:-0.035, 95% CI: -0.061, -0.010), or living alone (β:-0.033, 95% CI: -0.052, -0.014), than individuals who were married or cohabitating. One SD increase of LTL was associated with a lower risk of CVD (HR: 0.79, 95% CI: 0.66, 0.93). Individuals who were divorced or separated, widowed, or living alone had a higher risk of CVD than individuals who were married or cohabitating. The summary HR of CVD was 1.21 (95% CI: 1.08, 1.35) when comparing individuals who were living singly, regardless of reason, with the individuals who were married or cohabitating. LTL appeared to mediate little of the association between marital status and CVD (HR additionally adjusted for LTL: 1.20; 95% CI: 1.08, 1.34).CONCLUSIONS: Living singly, regardless of reason, was associated with a shorter LTL and a higher risk of CVD. The association between marital status and CVD was however not greatly attributable to telomere shortening.
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| 5. |
- Chen, Yongzhen, 1990-
(author)
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Image dipoles and polarons in organic semiconductors
- 2021
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Doctoral thesis (other academic/artistic)abstract
- The rapid development of organic electronics depends on the synthesis of new π-conjugated molecules/polymers and the exploration of fundamental physics. However, most of the efforts have been concentrated on the former, leading to a lack of thorough understanding of many important concepts, which will become the ultimate limiting factor for overall performance and applications. Thereinto, the interface energetics in multilayer stacked optoelectronic devices and the electronic structure of doped organic semiconductors are two of the most complicated and yet inevitable topics in this field. A better understanding of them can provide needed additional insights into the operation of devices and give valuable guidance for device and molecule design. Hence, the aim of this thesis is to investigate these two fundamental issues using various spectroscopic characterizations and supported by computational modeling.The cathode/organic interface plays a critical role in achieving balanced charge transport and improved stability in organic electronic devices. Employing stable cathode materials, however, typically results in large electron injection barriers and sub-optimal devices. Using small-molecule electron transport materials (ETMs) as interlayers is an effective approach to reduce the electron injection barriers, but the working mechanism is still under debate. By studying the energy level alignment behavior of ETMs on different types of substrates, we find the work function of the substrate is reduced by an extra “image” dipole formed at the interface and within the first layer of the ETM film. The use of non-reactive substrates and the results from X-ray photoelectron spectroscopy core level analysis exclude the orbital hybridization theory, which states that an ETM-metal complex may form at the interface. The characterization results on molecular orientation disqualify an explanation using intrinsic molecular dipole moments. Instead, experiments demonstrate that the interface dipole depends on the areal density and direction of lone electron pairs on the heteroatoms in ETMs, which is similar to previous observations in tertiary aliphatic amines. This behavior is well described by the so-called “double dipole step” model, where one dipole formed by the nitrogen nuclei and the lone pairs in the organic side points from the substrate surface to the organic film and the other one formed by their image charges in the electrode side shows the same direction.The polaron charge carrier is another important concept involved in multiple (opto)electronic processes during device operation, such as charge transport, exciton recombination/dissociation. Although numerous experimental and theoretical efforts have been made, there is still a lack of comprehensive studies on the electronic structure of negative polarons due to their high air sensitivity, including correlation between the valence band structure measured by ultraviolet photoelectron spectroscopy (UPS) and the optical band gap derived from the UV−vis−NIR absorption. In the present work, we are able to integrate the optical and electrical measurements with photoelectron spectroscopy to collect all information without breaking an ultra-high vacuum. Negative polarons formed in alkali metal-doped polymers are detected with new polaronic states below the Fermi level and lower energy absorption bands arising from the excitation from polaronic states to unoccupied states. In addition, the Fermi level shifts toward the conduction band with increasing the doping ratio, and the doubly-occupied polaronic state shows slightly lower energy than the topmost valance band peak of the neutral polymer. These observations are supported by the density functional theory (DFT) simulations, from which we also demonstrate that polaron pairs rather than bipolarons are preferentially formed at high doping ratios. By comparison of different polymer and dopant systems, we find the polymer-dopant interaction and the polaron delocalization are dependent on the distortion of the polymer backbone and the size of the dopant, properties that in turn affect the conductivity and air stability of the n-doped materials.I hope that the findings presented in the thesis can greatly promote the understanding of the energetics of the ETMs/cathode interface and the electronic structures of negative polarons in alkali metal-doped polymers, contributing to further providing new guidelines for the molecular design and improve the device performance.
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| 6. |
- Cui, Xiaolei, et al.
(author)
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Temperature-dependent electronic properties of inorganic-organic hybrid halide perovskite (CH3NH3PbBr3) single crystal
- 2017
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In: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 111:23
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Journal article (peer-reviewed)abstract
- In this paper, the temperature-dependent electronic properties of inorganic-organic hybrid halide perovskite (CH3NH3PbBr3) single crystals are investigated. The dynamic current-time measurement results at different temperatures directly demonstrate that the electrical properties of the perovskite single crystal are dependent on the work temperature. We find that the Poole-Frankel conduction mechanism fits the current-voltage curves at small bias voltage (0-1 V) under darkness, which is mainly attributed to the surface defect states. The capability of carriers de-trapping from defects varies with different work temperatures, resulting in an increased current as the temperature increases under both darkness and illumination. In addition, the different transient photocurrent responses of incident light at two wavelengths (470 nm, 550 nm) further confirm the existence of defect states on the single crystal surface. Published by AIP Publishing.
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| 7. |
- Dediu, V., et al.
(author)
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Room-temperature spintronic effects in Alq3 -based hybrid devices
- 2008
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:11
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Journal article (peer-reviewed)abstract
- We report on efficient spin polarized injection and transport in long (102 nm) channels of Alq3 organic semiconductor. We employ vertical spin valve devices with a direct interface between the bottom manganite electrode and Alq3, while the top-electrode geometry consists of an insulating tunnel barrier placed between the "soft" organic semiconductor and the top Co electrode. This solution reduces the ubiquitous problem of the so-called ill-defined layer caused by metal penetration, which extends into the organic layer up to distances of about 50-100 nm and prevents the realization of devices with well-defined geometry. For our devices the thickness is defined with an accuracy of about 2.5 nm, which is near the Alq3 molecular size. We demonstrate efficient spin injection at both interfaces in devices with 100- and 200-nm-thick channels. We solve one of the most controversial problems of organic spintronics: the temperature limitations for spin transport in Alq3 -based devices. We clarify this issue by achieving room-temperature spin valve operation through the improvement of spin injection properties of both ferromagnetic/ Alq3 interfaces. In addition, we discuss the nature of the inverse sign of the spin valve effect in such devices proposing a mechanism for spin transport. © 2008 The American Physical Society.
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| 8. |
- Ding, B.F., et al.
(author)
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Electroluminescence and magnetoresistance of the organic light-emitting diode with a La0.7 Sr0.3 Mn O3 anode
- 2008
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 93:18
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Journal article (peer-reviewed)abstract
- Electroluminescence (EL) with brightness up to 300 cd m2 is observed from organic light-emitting diodes fabricated on oxygen-treated La0.7 Sr0.3 Mn O 3 anodes. An external magnetic field of 150 mT applied parallel to the device surface can enhance the EL intensity by 10%, accompanied by a raised current efficiency. In-plane magnetization of the ferromagnetic anode is found to be the main origin of increase in the current contributable to EL, though magnetoresistance of the organic functional materials also plays a role in the EL enhancement observed in the magnetic field. © 2008 American Institute of Physics.
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| 9. |
- Hatamvand, Mohammad, et al.
(author)
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The role of different dopants of Spiro-OMeTAD hole transport material on the stability of perovskite solar cells : A mini review
- 2023
-
In: Vacuum. - 0042-207X. ; 214
-
Research review (peer-reviewed)abstract
- Perovskite solar cells (PSCs) have demonstrated rapid advancements in power conversion efficiency (PCE) in recent years, reaching 25.7% within a decade. However, the stability of PSCs lags behind in comparison, with short lifetimes being a major obstacle to commercialization. The various layers and interfaces within PSCs play a significant role in both PCE and stability. Spiro-OMeTAD is the most common hole-transport material (HTM) used in PSCs with n-i-p configuration, due to its high performance. However, Spiro-OMeTAD’s bulky structure leads to low hole mobility and conductivity, making it an inefficient hole transporter. Doping Spiro-OMeTAD with specific organic and inorganic materials can increase PCE, but also introduces side effects on PSC stability. This review focuses on the effects of dopants on the stability of PSCs using Spiro-OMeTAD HTM and offers suggestions for enhancing PSC stability through dopant engineering for the eventual commercialization of PSCs.
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| 10. |
- Ingre, Caroline, et al.
(author)
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Lipids, apolipoproteins, and prognosis of amyotrophic lateral sclerosis
- 2020
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In: Neurology. - Stockholm : Karolinska Institutet, Dept of Medical Epidemiology and Biostatistics. - 1526-632X.
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Journal article (peer-reviewed)abstract
- Objective: To determine whether lipids and apolipoproteins predict prognosis of patients with amyo- trophic lateral sclerosis in a cohort study of 99 patients with amyotrophic lateral sclerosis who were diagnosed during 2015 to 2018 and followed up until October 31, 2018, at the Neurology Clinic in Karolinska University Hospital in Stockholm, Sweden. Methods: Total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides, apolipoprotein AI, apolipoprotein B, and lipid ratios were measured at the time of amyotrophic lateral sclerosis diagnosis or shortly thereafter. Death after amyotrophic lateral sclerosis diagnosis was used as the main outcome. The Cox model was used to estimate hazard ratios with 95% confidence intervals of death after amyotrophic lateral sclerosis diagnosis, after controlling for sex, age at diagnosis, site of symptom onset, diagnostic delay, body mass index, Amyotrophic Lateral Sclerosis Functional Rating Scale–Revised score, and progression rate. Results: A 1-SD increase of total cholesterol (hazard ratio 0.60, 95% confidence interval 0.41–0.89, p = 0.01), low-density lipoprotein cholesterol (hazard ratio 0.64, 95% confidence interval 0.44–0.92, p = 0.02), low-density lipoprotein cholesterol/high-density lipoprotein cholesterol ratio (hazard ratio 0.65, 95% confidence interval 0.46–0.92, p = 0.02), apolipoprotein B (hazard ratio 0.62, 95% confidence interval 0.44–0.88, p = 0.01), or apolipoprotein B/apolipoprotein AI ratio (hazard ratio 0.61, 95% confidence interval 0.43–0.86, p < 0.01) was associated with a lower risk of death after amyotrophic lateral sclerosis diagnosis. A dose-response relationship was also noted when these biomarkers were analyzed as categorical variables. Conclusions: Lipids and apolipoproteins are important prognostic indicators for amyotrophic lateral sclerosis and should be monitored at the diagnosis of amyotrophic lateral sclerosis.
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