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Liu, Xianjie, Ph.D.
Publications (10 of 82) Show all publications
Wang, C., Ni, S., Braun, S., Fahlman, M. & Liu, X. (2019). Effects of water vapor and oxygen on non-fullerene small molecule acceptors. Journal of Materials Chemistry C, 7(4), 879-886
Open this publication in new window or tab >>Effects of water vapor and oxygen on non-fullerene small molecule acceptors
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2019 (English)In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 7, no 4, p. 879-886Article in journal (Refereed) Published
Abstract [en]

Due to the rapid development of non-fullerene acceptors (NFAs), the efficiency of organic solar cells is steadily being improved. The stability of organic solar cells also is expected to be enhanced with the introduction of the NFAs, yet the stability of NFAs themselves have been less investigated to date. In this paper, the stability of a set of typical NFAs was studied in situ employing photoelectron spectroscopy. The studied molecules show higher resistance to water vapor and thermal stress compared to fullerenes. For water vapor exposure, the highest occupied molecular orbital (HOMO) of NFAs undergoes only minor and reversible changes and the NFAs/substrate work function stays constant. Exposure to oxygen gas significantly modified the electronic structure of the NFAs and the effect was only partially reversible by annealing. However, the presence of water vapor was shown to slow down the degradation caused by oxygen. This is in stark contrast to fullerenes that undergo irreversible degradation upon water vapor exposure.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2019
National Category
Condensed Matter Physics Nano Technology
Identifiers
urn:nbn:se:liu:diva-154288 (URN)10.1039/C8TC05475D (DOI)000459571400007 ()2-s2.0-85060595857 (Scopus ID)
Note

Funding agencies: Knut and Alice Wallenberg Foundation project "Tail of the Sun; Swedish Research Council [2016-05498]; Swedish Foundation for Strategic Research [SE13-0060]; Ministry of Science and Technology [2016YFA0200700]; NSFC [21504066, 21534003]; Swedish Energy Age

Available from: 2019-02-01 Created: 2019-02-01 Last updated: 2019-03-20Bibliographically approved
Yang, J., Xiong, S., Qu, T., Zhang, Y., He, X., Guo, X., . . . Bao, Q. (2019). Extremely Low-Cost and Green Cellulose Passivating Perovskites for Stable and High-Performance Solar Cells. ACS Applied Materials and Interfaces, 11(14), 13491-13498
Open this publication in new window or tab >>Extremely Low-Cost and Green Cellulose Passivating Perovskites for Stable and High-Performance Solar Cells
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2019 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, no 14, p. 13491-13498Article in journal (Refereed) Published
Abstract [en]

The fast evolution of metal halide perovskite solar cells has opened a new chapter in the field of renewable energy. High-quality perovskite films as the active layers are essential for both high efficiency and long-term stability. Here, the perovskite films with enlarged crystal grain size and decreased defect density are fabricated by introducing the extremely low-cost and green polymer, ethyl cellulose (EC), into the perovskite layer. The addition of EC triggers hydrogen bonding interactions between EC and the perovskite, passivating the charge defect traps at the grain boundaries. The long chain of EC further acts as a scaffold for the perovskite structure, eliminating the annealing-induced lattice strain during the film fabrication process. The resulting devices with the EC additive exhibit a remarkably enhanced average power conversion efficiency from 17.11 to 19.27% and an improvement of all device parameters. The hysteresis index is found to decrease by three times from 0.081 to 0.027, which is attributed to suppressed ion migration and surface charge trapping. In addition, the defect passivation by EC significantly improves the environmental stability of the perovskite films, yielding devices that retain 80% of their initial efficiency after 30 days in ambient air at 45% relative humidity, whereas the pristine devices without EC fully degrade. This work provides a low-cost and green avenue for passivating defects that improves both the efficiency and operational stability of perovskite solar cells.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
Keywords
cellulose; passivation; perovskite solar cells; efficiency; stability
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-157220 (URN)10.1021/acsami.9b01740 (DOI)000464769400049 ()30880387 (PubMedID)2-s2.0-85064109044 (Scopus ID)
Note

Funding Agencies|National Science Foundation of China [11604099, 21875067, 51873138, 51811530011]; Shanghai Science and Technology Innovation Action Plan [19QA1403100, 17JC1402500]; National Key Project for Basic Research of China [2017YFA0303403]; Swedish Research Council [2016-05498]; STINT grant [CH2017-7163]

Available from: 2019-06-13 Created: 2019-06-13 Last updated: 2019-06-18Bibliographically approved
Adam, R. E., Chalangar, E., Pirhashemi, M., Pozina, G., Liu, X., Palisaitis, J., . . . Nur, O. (2019). Graphene-based plasmonic nanocomposites for highly enhanced solar-driven photocatalytic activities. RSC Advances, 9(52), 30585-30598
Open this publication in new window or tab >>Graphene-based plasmonic nanocomposites for highly enhanced solar-driven photocatalytic activities
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2019 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 9, no 52, p. 30585-30598Article in journal (Refereed) Published
Abstract [en]

High-efficiency photocatalysts are crucial for the removal of organic pollutants and environmental sustainability. In the present work, we report on a new low-temperature hydrothermal chemical method, assisted by ultrasonication, to synthesize disruptive plasmonic ZnO/graphene/Ag/AgI nanocomposites for solar-driven photocatalysis. The plasmonic nanocomposites were investigated by a wide range of characterization techniques, confirming successful formation of photocatalysts with excellent degradation efficiency. Using Congo red as a model dye molecule, our experimental results demonstrated a photocatalytic reactivity exceeding 90% efficiency after one hour simulated solar irradiation. The significantly enhanced degradation efficiency is attributed to improved electronic properties of the nanocomposites by hybridization of the graphene and to the addition of Ag/AgI which generates a strong surface plasmon resonance effect in the metallic silver further improving the photocatalytic activity and stability under solar irradiation. Scavenger experiments suggest that superoxide and hydroxyl radicals are responsible for the photodegradation of Congo red. Our findings are important for the fundamental understanding of the photocatalytic mechanism of ZnO/graphene/Ag/AgI nanocomposites and can lead to further development of novel efficient photocatalyst materials.

Place, publisher, year, edition, pages
Royal Meteorological Society, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-160568 (URN)10.1039/C9RA06273D (DOI)
Available from: 2019-09-30 Created: 2019-09-30 Last updated: 2019-10-07Bibliographically approved
Ibupoto, Z. H., Tahira, A., Tang, P., Liu, X., Morante, J. R., Fahlman, M., . . . Vomiero, A. (2019). MoSx@NiO Composite Nanostructures: An Advanced Nonprecious Catalyst for Hydrogen Evolution Reaction in Alkaline Media. Advanced Functional Materials, 29(7), Article ID 1807562.
Open this publication in new window or tab >>MoSx@NiO Composite Nanostructures: An Advanced Nonprecious Catalyst for Hydrogen Evolution Reaction in Alkaline Media
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2019 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 29, no 7, article id 1807562Article in journal (Refereed) Published
Abstract [en]

The design of the earth-abundant, nonprecious, efficient, and stable electrocatalysts for efficient hydrogen evolution reaction (HER) in alkaline media is a hot research topic in the field of renewable energies. A heterostructured system composed of MoSx deposited on NiO nanostructures (MoSx@NiO) as a robust catalyst for water splitting is proposed here. NiO nanosponges are applied as cocatalyst for MoS2 in alkaline media. Both NiO and MoS2@NiO composites are prepared by a hydrothermal method. The NiO nanostructures exhibit sponge-like morphology and are completely covered by the sheet-like MoS2. The NiO and MoS2 exhibit cubic and hexagonal phases, respectively. In the MoSx@NiO composite, the HER experiment in 1 m KOH electrolyte results in a low overpotential (406 mV) to produce 10 mA cm(-2) current density. The Tafel slope for that case is 43 mV per decade, which is the lowest ever achieved for MoS2-based electrocatalyst in alkaline media. The catalyst is highly stable for at least 13 h, with no decrease in the current density. This simple, cost-effective, and environmentally friendly methodology can pave the way for exploitation of MoSx@NiO composite catalysts not only for water splitting, but also for other applications such as lithium ion batteries, and fuel cells.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2019
Keywords
alkaline media; electrolysis; MoSx@NiO composites
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-155574 (URN)10.1002/adfm.201807562 (DOI)000459719800018 ()2-s2.0-85059344786 (Scopus ID)
Note

Funding Agencies|Knut and Alice Wallenberg Foundation; Kempe Foundation; LTU Lab fund program; Generalitat de Catalunya [2017 SGR 327, JRM 2017 SGR 1246]; Spanish MINECO project [ENE2017-85087-C3]; Severo Ochoa Programme (MINECO) [SEV-2013-0295-17-1]; CERCA Programme/Generalitat de Catalunya

Available from: 2019-03-20 Created: 2019-03-20 Last updated: 2019-08-30Bibliographically approved
Pirhashemi, M., Elhag, S., Elhadi Adam, R., Habibi-Yangjeh, A., Liu, X., Willander, M. & Nur, O. (2019). n–n ZnO–Ag2CrO4 heterojunction photoelectrodes with enhanced visible-light photoelectrochemical properties. RSC Advances, 9(14), 7992-8001
Open this publication in new window or tab >>n–n ZnO–Ag2CrO4 heterojunction photoelectrodes with enhanced visible-light photoelectrochemical properties
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2019 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 9, no 14, p. 7992-8001Article in journal (Refereed) Published
Abstract [en]

In this study, ZnO nanorods (NRs) were hydrothermally grown on an Au-coated glass substrate at a relatively low temperature (90 °C), followed by the deposition of Ag2CrO4 particles via a successive ionic layer adsorption and reaction (SILAR) route. The content of the Ag2CrO4 particles on ZnO NRs was controlled by changing the number of SILAR cycles. The fabricated ZnO–Ag2CrO4 heterojunction photoelectrodes were subjected to morphological, structural, compositional, and optical property analyses; their photoelectrochemical (PEC) properties were investigated under simulated solar light illumination. The photocurrent responses confirmed that the ability of the ZnO–Ag2CrO4 heterojunction photoelectrodes to separate the photo-generated electron–hole pairs is stronger than that of bare ZnO NRs. Impressively, the maximum photocurrent density of about 2.51 mA cm−2 at 1.23 V (vs. Ag/AgCl) was measured for the prepared ZnO–Ag2CrO4 photoelectrode with 8 SILAR cycles (denoted as ZnO–Ag2CrO4-8), which exhibited about 3-fold photo-enhancement in the current density as compared to bare ZnO NRs (0.87 mA cm−2) under similar conditions. The improvement in photoactivity was attributed to the ideal band gap and high absorption coefficient of the Ag2CrO4 particles, which resulted in improved solar light absorption properties. Furthermore, an appropriate annealing treatment was proven to be an efficient process to increase the crystallinity of Ag2CrO4 particles deposited on ZnO NRs, which improved the charge transport characteristics of the ZnO–Ag2CrO4-8 photoelectrode annealed at 200 °C and increased the performance of the photoelectrode. The results achieved in the present work present new insights for designing n–n heterojunction photoelectrodes for efficient and cost-effective PEC applications and solar-to-fuel energ

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-155657 (URN)10.1039/C9RA00639G (DOI)000462646000051 ()2-s2.0-85062919263 (Scopus ID)
Note

Funding agencies: University of Mohaghegh Ardabili-Iran and Linkoping University-Sweden; AForsk [17-457

Available from: 2019-03-22 Created: 2019-03-22 Last updated: 2019-04-18Bibliographically approved
Xu, W., Hu, Q., Bai, S., Bao, C., Miao, Y., Yuan, Z., . . . Gao, F. (2019). Rational molecular passivation for high-performance perovskite light-emitting diodes. Nature Photonics, 13(6), 418-424
Open this publication in new window or tab >>Rational molecular passivation for high-performance perovskite light-emitting diodes
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2019 (English)In: Nature Photonics, ISSN 1749-4885, E-ISSN 1749-4893, Vol. 13, no 6, p. 418-424Article in journal (Refereed) Published
Abstract [en]

A major efficiency limit for solution-processed perovskite optoelectronic devices, for example light-emitting diodes, is trap-mediated non-radiative losses. Defect passivation using organic molecules has been identified as an attractive approach to tackle this issue. However, implementation of this approach has been hindered by a lack of deep understanding of how the molecular structures influence the effectiveness of passivation. We show that the so far largely ignored hydrogen bonds play a critical role in affecting the passivation. By weakening the hydrogen bonding between the passivating functional moieties and the organic cation featuring in the perovskite, we significantly enhance the interaction with defect sites and minimize non-radiative recombination losses. Consequently, we achieve exceptionally high-performance near-infrared perovskite light-emitting diodes with a record external quantum efficiency of 21.6%. In addition, our passivated perovskite light-emitting diodes maintain a high external quantum efficiency of 20.1% and a wall-plug efficiency of 11.0% at a high current density of 200 mA cm−2, making them more attractive than the most efficient organic and quantum-dot light-emitting diodes at high excitations.

Place, publisher, year, edition, pages
Springer Nature Publishing AG, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-157707 (URN)10.1038/s41566-019-0390-x (DOI)000468752300019 ()
Note

Funding agencies:  ERC Starting Grant [717026]; National Basic Research Program of China (973 Program) [2015CB932200]; National Natural Science Foundation of China [61704077, 51572016, 51721001, 61634001, 61725502, 91733302, U1530401]; Natural Science Foundation of Jiangsu 

Available from: 2019-06-19 Created: 2019-06-19 Last updated: 2019-10-10Bibliographically approved
Elhadi Adam, R., Pirhashemi, M., Elhag, S., Liu, X., Habibi-Yangjeh, A., Willander, M. & Nur, O. (2019). ZnO/Ag/Ag2WO4 photo-electrodes with plasmonic behavior for enhanced photoelectrochemical water oxidation. RSC Advances, 9(15), 8271-8279
Open this publication in new window or tab >>ZnO/Ag/Ag2WO4 photo-electrodes with plasmonic behavior for enhanced photoelectrochemical water oxidation
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2019 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 9, no 15, p. 8271-8279Article in journal (Refereed) Published
Abstract [en]

Ag-based compounds are excellent co-catalyst that can enhance harvesting visible light and increase photo-generated charge carrier separation owing to its surface plasmon resonance (SPR) effect in photoelectrochemical (PEC) applications. However, the PEC performance of a ZnO/Ag/Ag2WO4 heterostructure with SPR behavior has not been fully studied so far. Here we report the preparation of a ZnO/Ag/Ag2WO4 photo-electrode with SPR behavior by a low temperature hydrothermal chemical growth method followed by a successive ionic layer adsorption and reaction (SILAR) method. The properties of the prepared samples were investigated by different characterization techniques, which confirm that Ag/Ag2WO4 was deposited on the ZnO NRs. The Ag2WO4/Ag/ZnO photo-electrode showed an enhancement in PEC performance compared to bare ZnO NRs. The observed enhancement is attributed to the red shift of the optical absorption spectrum of the Ag2WO4/Ag/ZnO to the visible region (>400 nm) and to the SPR effect of surface metallic silver (Ag0) particles from the Ag/Ag2WO4 that could generate electron–hole pairs under illumination of low energy visible sun light. Finally, we proposed the PEC mechanism of the Ag2WO4/Ag/ZnO photo-electrode with an energy band structure and possible electron–hole separation and transportation in the ZnO/Ag/Ag2WO4 heterostructure with SPR effect for water oxidation. ER

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-155655 (URN)10.1039/C8RA10141H (DOI)000461445300016 ()
Available from: 2019-03-22 Created: 2019-03-22 Last updated: 2019-04-08Bibliographically approved
Li, Z., Sun, H., Hsiao, C.-L., Yao, Y., Xiao, Y., Shahi, M., . . . Zhang, F. (2018). A Free-Standing High-Output Power Density Thermoelectric Device Based on Structure-Ordered PEDOT:PSS. Advanced Electronic Materials, 4(2), Article ID 1700496.
Open this publication in new window or tab >>A Free-Standing High-Output Power Density Thermoelectric Device Based on Structure-Ordered PEDOT:PSS
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2018 (English)In: Advanced Electronic Materials, ISSN 2199-160X, Vol. 4, no 2, article id 1700496Article in journal (Refereed) Published
Abstract [en]

A free-standing high-output power density polymeric thermoelectric (TE) device is realized based on a highly conductive (approximate to 2500 S cm(-1)) structure-ordered poly(3,4-ethylenedioxythiophene):polystyrene sulfonate film (denoted as FS-PEDOT:PSS) with a Seebeck coefficient of 20.6 mu V K-1, an in-plane thermal conductivity of 0.64 W m(-1) K-1, and a peak power factor of 107 mu W K-2 m(-1) at room temperature. Under a small temperature gradient of 29 K, the TE device demonstrates a maximum output power density of 99 +/- 18.7 mu W cm(-2), which is the highest value achieved in pristine PEDOT:PSS based TE devices. In addition, a fivefold output power is demonstrated by series connecting five devices into a flexible thermoelectric module. The simplicity of assembling the films into flexible thermoelectric modules, the low out-of-plane thermal conductivity of 0.27 W m(-1) K-1, and free-standing feature indicates the potential to integrate the FS-PEDOT:PSS TE modules with textiles to power wearable electronics by harvesting human bodys heat. In addition to the high power factor, the high thermal stability of the FS-PEDOT:PSS films up to 250 degrees C is confirmed by in situ temperature-dependent X-ray diffraction and grazing incident wide angle X-ray scattering, which makes the FS-PEDOT:PSS films promising candidates for thermoelectric applications.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2018
Keywords
free-standing PEDOT:PSS film; output power density; p-type; thermoelectric generators
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:liu:diva-145465 (URN)10.1002/aelm.201700496 (DOI)000424888600015 ()2-s2.0-85039784826 (Scopus ID)
Note

Funding Agencies|Vinnova Marie Curie incoming project [2016-04112]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [200900971]; Recruitment Program of Global Youth Experts; National Natural Science Foundation of China [21474035]; United States National Science Foundation [DMR-1262261]; Open Fund of the State Key Laboratory of Luminescent Materials and Devices [2016-skllmd-03]; European Research Council [ERC 307596]

Available from: 2018-03-13 Created: 2018-03-13 Last updated: 2018-04-09Bibliographically approved
Wijeratne, K., Ail, U., Brooke, R., Vagin, M., Liu, X., Fahlman, M. & Crispin, X. (2018). Bulk electronic transport impacts on electron transfer at conducting polymer electrode-electrolyte interfaces.. Proceedings of the National Academy of Sciences of the United States of America (7), 11899-11904
Open this publication in new window or tab >>Bulk electronic transport impacts on electron transfer at conducting polymer electrode-electrolyte interfaces.
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2018 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, no 7, p. 11899-11904Article in journal (Refereed) Epub ahead of print
Abstract [en]

Electrochemistry is an old but still flourishing field of research due to the importance of the efficiency and kinetics of electrochemical reactions in industrial processes and (bio-)electrochemical devices. The heterogeneous electron transfer from an electrode to a reactant in the solution has been well studied for metal, semiconductor, metal oxide, and carbon electrodes. For those electrode materials, there is little correlation between the electronic transport within the electrode material and the electron transfer occurring at the interface between the electrode and the solution. Here, we investigate the heterogeneous electron transfer between a conducting polymer electrode and a redox couple in an electrolyte. As a benchmark system, we use poly(3,4-ethylenedioxythiophene) (PEDOT) and the Ferro/ferricyanide redox couple in an aqueous electrolyte. We discovered a strong correlation between the electronic transport within the PEDOT electrode and the rate of electron transfer to the organometallic molecules in solution. We attribute this to a percolation-based charge transport within the polymer electrode directly involved in the electron transfer. We show the impact of this finding by optimizing an electrochemical thermogalvanic cell that transforms a heat flux into electrical power. The power generated by the cell increased by four orders of magnitude on changing the morphology and conductivity of the polymer electrode. As all conducting polymers are recognized to have percolation transport, we believe that this is a general phenomenon for this family of conductors.

Place, publisher, year, edition, pages
National academy of sciences, 2018
Keywords
conducting polymer, electron transfer, thermogalvanic cell
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-152759 (URN)10.1073/pnas.1806087115 (DOI)000450642800036 ()30397110 (PubMedID)
Note

Funding agencies: Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University Faculty Grant [SFO-Mat-LiU 2009-00971]

Available from: 2018-11-20 Created: 2018-11-20 Last updated: 2019-03-21
Zuo, G., Liu, X., Fahlman, M. & Kemerink, M. (2018). High Seebeck Coefficient in Mixtures of Conjugated Polymers. Paper presented at 2018/05/14. Advanced Functional Materials, 28(15), Article ID 1703280.
Open this publication in new window or tab >>High Seebeck Coefficient in Mixtures of Conjugated Polymers
2018 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 28, no 15, article id 1703280Article in journal (Refereed) Published
Abstract [en]

A universal method to obtain record?high electronic Seebeck coefficients is demonstrated while preserving reasonable conductivities in doped blends of organic semiconductors through rational design of the density of states (DOSs). A polymer semiconductor with a shallow highest occupied molecular orbital (HOMO) level?poly(3?hexylthiophene) (P3HT) is mixed with materials with a deeper HOMO (PTB7, TQ1) to form binary blends of the type P3HTx:B1?x (0 ≤ x ≤ 1) that is p?type doped by F4TCNQ. For B = PTB7, a Seebeck coefficient S = 1100 µV K?1 with conductivity σ = 0.3 S m?1 at x = 0.10 is achieved, while for B = TQ1, S = 2000 µV K?1 and σ = 0.03 S m?1 at x = 0.05 is found. Kinetic Monte Carlo simulations with parameters based on experiments show good agreement with the experimental results, confirming the intended mechanism. The simulations are used to derive a design rule for parameter tuning. These results can become relevant for low?power, low?cost applications like (providing power to) autonomous sensors, in which a high Seebeck coefficient translates directly to a proportionally reduced number of legs in the thermogenerator, and hence in reduced fabrication cost and complexity.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2018
Keywords
conjugated polymers, doping, kinetic Monte Carlo simulations, organic thermoelectrics, Seebeck coefficients
National Category
Materials Engineering Physical Sciences
Identifiers
urn:nbn:se:liu:diva-147779 (URN)10.1002/adfm.201703280 (DOI)000430101100004 ()
Conference
2018/05/14
Note

Funding Agencies: Chinese Scholarship Council (CSC)

Available from: 2018-05-14 Created: 2018-05-14 Last updated: 2018-05-31Bibliographically approved
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