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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
Fahlman, M., Fabiano, S., Gueskine, V., Simon, D. T., Berggren, M. & Crispin, X. (2019). Interfaces in organic electronics. Nature Reviews Materials
Open this publication in new window or tab >>Interfaces in organic electronics
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2019 (English)In: Nature Reviews Materials, E-ISSN 2058-8437Article in journal (Refereed) Epub ahead of print
Abstract [en]

Undoped, conjugated, organic molecules and polymers possess properties of semiconductors, including the electronic structure and charge transport, which can be readily tuned by chemical design. Moreover, organic semiconductors (OSs) can be n-doped or p-doped to become organic conductors and can exhibit mixed electronic and ionic conductivity. Compared with inorganic semiconductors and metals, organic (semi)conductors possess a unique feature: no insulating oxide forms on their surface when exposed to air. Thus, OSs form clean interfaces with many materials, including metals and other OSs. OS–metal and OS–OS interfaces have been intensely investigated over the past 30 years, from which a consistent theoretical description has emerged. Since the 2000s, increased attention has been paid to interfaces in organic electronics that involve dielectrics, electrolytes, ferroelectrics and even biological organisms. In this Review, we consider the central role of these interfaces in the function of organic electronic devices and discuss how the physico-chemical properties of the interfaces govern the interfacial transport of light, excitons, electrons and ions, as well as the transduction of electrons into the molecular language of cells.

Place, publisher, year, edition, pages
Nature Publishing Group, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-160114 (URN)10.1038/s41578-019-0127-y (DOI)2-s2.0-85069828729 (Scopus ID)
Available from: 2019-09-05 Created: 2019-09-05 Last updated: 2019-09-10Bibliographically 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
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: 2019-07-01Bibliographically approved
Guo, X., Li, D., Zhang, Y., Jan, M., Xu, J., Wang, Z., . . . Bao, Q. (2019). Understanding the effect of N2200 on performance of J71: ITIC bulk heterojunction in ternary non-fullerene solar cells. Organic electronics, 71, 65-71
Open this publication in new window or tab >>Understanding the effect of N2200 on performance of J71: ITIC bulk heterojunction in ternary non-fullerene solar cells
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2019 (English)In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 71, p. 65-71Article in journal (Refereed) Published
Abstract [en]

None-fullerene solar cells with ternary architecture have attracted much attention because it is an effective approach for boosting the device power conversion efficiency. Here, the crystalline polymer N2200 as the third component is integrated into J71: ITIC bulk heterojunction. A series of characterizations indicate that N2200 could increase photo-harvesting, balanced hole and electron mobilities, enhanced exciton dissociation, and suppressed charge recombination, which result in the comprehensive improvement of open circuit voltage, short circuit current and fill factor in the device. Moreover, after introduction of N2200, the morphology of the ternary active layer is optimized, and the film crystallinity is improved. This work demonstrates that adding a small quantity of high crystallization acceptor into non-fullerene donor: acceptor mixture is a promising strategy toward developing high-performance organic solar cells.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
None-fullerene; Interface; Charge recombination; Efficiency; Ternary organic solar cells
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-158534 (URN)10.1016/j.orgel.2019.05.004 (DOI)000469838800010 ()2-s2.0-85065828560 (Scopus ID)
Note

Funding Agencies|National Science Foundation of China [11604099, 21875067, 51873138, 51811530011]; Shanghai Rising -Star [19QA1403100]; Shanghai Science and Technology Innovation Action Plan [17JC1402500]; National Key Project for Basic Research of China [2017YFA0303403]; Swedish Research Council [2016-05498]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; STINT grant [CH2017-7163]

Available from: 2019-07-03 Created: 2019-07-03 Last updated: 2019-08-13Bibliographically 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
Wang, C., Ouyang, L., Xu, X., Braun, S., Liu, X. & Fahlman, M. (2018). Relationship of Ionization Potential and Oxidation Potential of Organic Semiconductor Films Used in Photovoltaics. Solar RRL, 2(9)
Open this publication in new window or tab >>Relationship of Ionization Potential and Oxidation Potential of Organic Semiconductor Films Used in Photovoltaics
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2018 (English)In: Solar RRL, ISSN 2367-198X, Vol. 2, no 9Article in journal (Refereed) Published
Abstract [en]

Ultraviolet photoelectron spectroscopy (UPS) and cyclic voltammetry (CV) are employed to measure energy levels for charge transport in organic semiconductor films. A series of classical molecules/polymers used in organic bulk heterojunction solar cells are deposited on platinum substrates/electrodes to form thin films and a linear relationship of vertical ionization potential (IP) measured by UPS and relative oxidation potential (Eox) obtained by CV is found, with a slope equal to unity. The intercept varies with the different reference redox couples and repeated potential sweep numbers during experiment processes. The relationship provides for an easy conversion of values obtained by the two techniques and correlates well with device parameters. The precision in the CV-derived IP values is not sufficient, however, to enable precise design of energy level alignment at heterojunction and the approach does not improve upon the current ?best practice? for obtaining donor ionization potential?acceptor electron affinity gaps at heterojunctions.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2018
Keywords
cyclic voltammetry, ionization potential, linear relationship, organic photovoltaics, oxidation potential, semiconductor films, UV photoelectron spectroscopy
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-151711 (URN)10.1002/solr.201800122 (DOI)000443972900011 ()
Funder
Swedish Foundation for Strategic Research , SE13‐0060Knut and Alice Wallenberg FoundationSwedish Research Council, 2016‐05498Linköpings universitet, 2009 00971Göran Gustafsson Foundation for Research in Natural Sciences and Medicine
Available from: 2018-10-03 Created: 2018-10-03 Last updated: 2018-10-10Bibliographically approved
Bao, Q., Liu, X., Braun, S., Yanqing, L., Jianxin, T., Chungang, D. & Fahlman, M. (2017). Intermixing Effect on Electronic Structures of TQ1:PC71BM Bulk Heterojunction in Organic Photovoltaics. Solar RRL, 1(10), Article ID 1700142.
Open this publication in new window or tab >>Intermixing Effect on Electronic Structures of TQ1:PC71BM Bulk Heterojunction in Organic Photovoltaics
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2017 (English)In: Solar RRL, ISSN 2367-198X, Vol. 1, no 10, article id 1700142Article in journal (Refereed) Published
Abstract [en]

The interface energetics and intermixing effects of the donor/acceptor bulk heterojunction (BHJ) blends of poly[2,3‐bis‐(3‐octyloxyphenyl) quinoxaline‐5, 8‐dilyl‐alt‐thiophene‐2, 5‐diyl]: [6,6]‐phenyl C71butyric acid methyl ester (TQ1:PC71BM) have been investigated using ultraviolet photoemission spectroscopy (UPS) in combination with the integer charge transfer model. The TQ1:PC71BM represents the useful model system for BHJ organic photovoltaics featuring effective charge generation and transport. It finds out that the positive integer charge state of TQ1 are equal in energy to the negative integer charge state of PC71BM, leading to a negligible potential step at TQ1:PC71BM interface and thus the vacuum level alignment. It is observed that the TQ1 accumulates on the top of TQ1:PC71BM BHJ and UPS spectra as function of various blend ratios suggest that the TQ1 mixes finely with PC71BM with the little work function modification in a wide range. In addition, no significant influence of the long‐range Coulomb interactions or the intermolecular hybridization on the occupied electronic structures is present for the well‐intermixed TQ1:PC71BM BHJs. These findings provide deep insights into the properties of BHJ blends and are beneficial for the performance optimization in organic photovoltaics.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2017
National Category
Physical Chemistry
Identifiers
urn:nbn:se:liu:diva-150513 (URN)10.1002/solr.201700142 (DOI)
Available from: 2018-08-23 Created: 2018-08-23 Last updated: 2019-01-09Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-9879-3915

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