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Ma, Zaifei
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Publications (10 of 22) Show all publications
Gedefaw, D., Zaifei, Z., Mulugeta, E., Zhao, Y., Zhang, F., Andersson, M. R. & Mammo, W. (2016). An alternating copolymer of fluorene donor and quinoxaline acceptor versus a terpolymer consisting of fluorene, quinoxaline and benzothiadiazole building units: synthesis and characterization. Polymer Bulletin, 73(4), 1167-1183
Open this publication in new window or tab >>An alternating copolymer of fluorene donor and quinoxaline acceptor versus a terpolymer consisting of fluorene, quinoxaline and benzothiadiazole building units: synthesis and characterization
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2016 (English)In: Polymer Bulletin, ISSN 0170-0839, E-ISSN 1436-2449, Vol. 73, no 4, p. 1167-1183Article in journal (Refereed) Published
Abstract [en]

An alternating polyfluorene copolymer based on fluorene donor and quinoxaline acceptor (P1) and an alternating terpolymer (P2) with fluorene (50 %) donor and quinoxaline (25 %) and benzothiadiazole (25 %) acceptor units were designed and synthesized for use as photoactive materials in solar cells. The presence of benzothiadiazole unit in P2 increased the optical absorption coverage in the range of 350-600 nm, which is an interesting property and a big potential for achieving improved photovoltaic performances with judicious optimization of the devices. Solar cells were fabricated from 1:4 blends of polymers-PCBM[70] using o-dichlorobenzene (o-DCB) as processing solvent, and P1 showed a power conversion efficiency (PCE) of 3.18 %, with a short-circuit current density (J (SC)) of 7.78 mA/cm(2), an open-circuit voltage (V (OC)) of 0.82 V, and a fill factor (FF) of 50 % while P2 showed an overall PCE of 2.14 % with corresponding J (SC) of 5.97 mA/cm(2), V (OC) of 0.84 V and FF of 42 %. In general, P2 gave lower J (SC) and FF presumably due to the fine domain sizes of the polymer-PCBM[70] blend as seen from the atomic force microscopy (AFM) image which might have affected the charge carrier transport. Alternating (P1) and ternary (P2) conjugated polymers were designed, synthesized and used for fabrication of photovoltaic devices. [GRAPHICS] .

Place, publisher, year, edition, pages
SPRINGER, 2016
Keywords
Polyfluorenes; Suzuki coupling reaction; Fluorene; Quinoxaline; Benzothiadiazole
National Category
Biological Sciences
Identifiers
urn:nbn:se:liu:diva-127259 (URN)10.1007/s00289-015-1541-y (DOI)000372614700016 ()
Note

Funding Agencies|International Science Programme (ISP), Uppsala University, Sweden

Available from: 2016-04-20 Created: 2016-04-19 Last updated: 2018-03-21
Bai, S., Jin, Y., Liang, X., Ye, Z., Wu, Z., Sun, B., . . . Zhang, F. (2015). Ethanedithiol Treatment of Solution-Processed ZnO Thin Films: Controlling the Intragap States of Electron Transporting Interlayers for Efficient and Stable Inverted Organic Photovoltaics. ADVANCED ENERGY MATERIALS, 5(5), 1401606
Open this publication in new window or tab >>Ethanedithiol Treatment of Solution-Processed ZnO Thin Films: Controlling the Intragap States of Electron Transporting Interlayers for Efficient and Stable Inverted Organic Photovoltaics
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2015 (English)In: ADVANCED ENERGY MATERIALS, ISSN 1614-6832, Vol. 5, no 5, p. 1401606-Article in journal (Refereed) Published
Abstract [en]

The surface defects of solution-processed ZnO films lead to various intragap states. When the solution-processed ZnO films are used as electron transport interlayers (ETLs) in inverted organic solar cells, the intragap states act as interfacial recombination centers for photogenerated charges and thereby degrade the device performance. Here, a simple passivation method based on ethanedithiol (EDT) treatment is demonstrated, which effectively removes the surface defects of the ZnO nanocrystal films by forming zinc ethanedithiolates. The passivation by EDT treatment modulates the intragap states of the ZnO films and introduces a new intragap band. When the EDT-treated ZnO nanocrystal films are used as ETLs in inverted organic solar cells, both the power conversion efficiency and stability of the devices are improved. The control studies show that the solar cells with EDT-treated ZnO films exhibit reduced charge recombination rates and enhanced charge extraction properties. These features are consistent with the fact that the modulation of the intragap states results in reduction of interfacial recombination as well as the improved charge selectivity and electron transport properties of the ETLs. It is further demonstrated that the EDT treatment-based passivation method can be extended to ZnO films deposited from sol-gel precursors.

Place, publisher, year, edition, pages
Wiley-VCH Verlag, 2015
Keywords
electron transporting interlayers; intragap states; molecular passivation; organic solar cells; ZnO thin films
National Category
Biological Sciences
Identifiers
urn:nbn:se:liu:diva-116817 (URN)10.1002/aenm.201401606 (DOI)000350754800013 ()
Note

Funding Agencies|National High Technology Research and Development Program of China [2011AA050520]; National Basic Research Program of China (973 Program) [2012CB932402]; National Natural Science Foundation of China [51172203]; Natural Science Funds for Distinguished Young Scholar of Zhejiang Province [R4110189]; Public Welfare Project of Zhejiang Province [2013C31057]; Swedish Energy Agency (Energimyndigheten); Swedish Research Council (VR); European Commission under a Marie Curie Intra-European Fellowship for Career Development

Available from: 2015-04-07 Created: 2015-04-07 Last updated: 2015-06-03
Qian, D., Liu, B., Wang, S., Himmelberger, S., Linares, M., Vagin, M., . . . Zhang, F. (2015). Modulating molecular aggregation by facile heteroatom substitution of diketopyrrolopyrrole based small molecules for efficient organic solar cells. Journal of Materials Chemistry A, 3(48), 24349-24357
Open this publication in new window or tab >>Modulating molecular aggregation by facile heteroatom substitution of diketopyrrolopyrrole based small molecules for efficient organic solar cells
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2015 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 48, p. 24349-24357Article in journal (Refereed) Published
Abstract [en]

In conjugated polymers and small molecules of organic solar cells, aggregation induced by intermolecular interactions governs the performance of photovoltaics. However, little attention has been paid to the connection between molecular structure and aggregation within solar cells based on soluble small molecules. Here we demonstrate modulation of intermolecular aggregation of two synthesized molecules through heteroatom substitution to develop an understanding of the role of aggregation in conjugated molecules. Molecule 1 (M1) based on 2-ethylhexyloxy-benzene substituted benzo[1,2-b:4,5-b]dithiophene (BDTP) and diketopyrrolopyrrole (DPP) displays strong aggregation in commonly used organic solvents, which is reduced in molecule 2 (M2) by facile oxygen atom substitution on the BDTP unit confirmed by absorption spectroscopy and optical microscopy, while it successfully maintains molecular planarity and favorable charge transport characteristics. Solar cells based on M2 exhibit more than double the photocurrent of devices based on M1 and yield a power conversion efficiency of 5.5%. A systematic investigation of molecular conformation, optoelectronic properties, molecular packing and crystallinity as well as film morphology reveals structure dependent aggregation responsible for the performance difference between the two conjugated molecules.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2015
National Category
Biological Sciences Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-123846 (URN)10.1039/c5ta06501a (DOI)000366163000022 ()
Note

Funding Agencies|Swedish Energy Agency; China Scholarship Council (CSC)

Available from: 2016-01-11 Created: 2016-01-11 Last updated: 2017-12-01
Ma, Z., Dang, D., Tang, Z., Gedefaw, D., Bergqvist, J., Zhu, W., . . . Wang, E. (2014). A Facile Method to Enhance Photovoltaic Performance of Benzodithiophene-Isoindigo Polymers by Inserting Bithiophene Spacer. ADVANCED ENERGY MATERIALS, 4(6)
Open this publication in new window or tab >>A Facile Method to Enhance Photovoltaic Performance of Benzodithiophene-Isoindigo Polymers by Inserting Bithiophene Spacer
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2014 (English)In: ADVANCED ENERGY MATERIALS, ISSN 1614-6832, Vol. 4, no 6Article in journal (Refereed) Published
Abstract [en]

A series of conjugated polymers containing benzodithiophene as donor and isoindigo as acceptor with no, one, two and three thiophene spacer groups is synthesized and characterized. The polymer with bithiophene as a spacer has a superior efficiency of 7.31% in solar cells. This demonstrates an important design strategy to produce polymers for high-performance solar cells by inserting thiophene spacer groups.

Place, publisher, year, edition, pages
Wiley-VCH Verlag, 2014
Keywords
conjugated polymers; energy conversion; fullerenes; photochemistry; solar cells
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-106976 (URN)10.1002/aenm.201301455 (DOI)000334790000008 ()
Available from: 2014-06-04 Created: 2014-06-02 Last updated: 2014-06-04
Gedefaw, D. A., Zhou, Y., Ma, Z., Genene, Z., Hellstrom, S., Zhang, F., . . . Andersson, M. R. (2014). Conjugated polymers with polar side chains in bulk heterojunction solar cell devices. Polymer international, 63(1), 22-30
Open this publication in new window or tab >>Conjugated polymers with polar side chains in bulk heterojunction solar cell devices
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2014 (English)In: Polymer international, ISSN 0959-8103, E-ISSN 1097-0126, Vol. 63, no 1, p. 22-30Article in journal (Refereed) Published
Abstract [en]

Two polymers with polar side chains, namely poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(5,8-di-2-thienyl-(2,3-bis(3-(2-(2-methoxyethoxy)ethoxy)phenyl)quinoxaline))] (P1) and poly[2,7-(9,9-bis(2-(2-methoxyethoxy)ethyl)fluorene)-alt-5,5-(5,8-di-2-thienyl-(2,3-bis(3-(2-(2-methoxyethoxy)-ethoxy)phenyl)quinoxaline))] (P2), were synthesized for solar cell application. A series of bulk heterojunction solar cells were systematically fabricated and characterized by varying the electron-acceptor materials, processing solvents and thickness of the active layer. The results show that P1, with a higher molecular weight and good film-forming properties, performed better. The best device showed an open circuit voltage of 0.87 V, a short circuit current of 6.81 mA cm(-2) and a power conversion efficiency of 2.74% with 1:4 polymer:[6,6]-phenyl-C71-butyric acid methyl ester (PCBM[70]) mixture using o-dichlorobenzene (o-DCB) as processing solvent. P2 on the other hand showed a poorer performance with chlorobenzene as processing solvent, but a much improved performance was obtained using o-DCB instead. Thus, an open circuit voltage of 0.80 V, short circuit current of 6.21 mA cm(-2) and an overall power conversion efficiency of 2.22% were recorded for a polymer:PCBM[70] mixing ratio of 1:4. This is presumably due to the improvement of the morphology of the active layer using o-DCB as processing solvent.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2014
Keywords
conjugated polymer, polar polymer, power conversion efficiency, donor-acceptor-donor
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-102845 (URN)10.1002/pi.4600 (DOI)000327997800004 ()
Note

Funding Agencies|International Science Programmes, Uppsala University, Sweden||

Available from: 2014-01-07 Created: 2014-01-02 Last updated: 2017-12-06
Gedefaw, D. A., Ma, Z., Henriksson, P., Zhang, F., Andersson, M. R. & Mammo, W. (2014). RANDOM POLYFLUORENE CO-POLYMERS DESIGNED FOR A BETTER OPTICAL ABSORPTION COVERAGE OF THE VISIBLE REGION OF THE ELECTROMAGNETIC SPECTRUM. Bulletin of the Chemical Society of Ethiopia, 28(1), 121-130
Open this publication in new window or tab >>RANDOM POLYFLUORENE CO-POLYMERS DESIGNED FOR A BETTER OPTICAL ABSORPTION COVERAGE OF THE VISIBLE REGION OF THE ELECTROMAGNETIC SPECTRUM
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2014 (English)In: Bulletin of the Chemical Society of Ethiopia, ISSN 1011-3924, E-ISSN 1726-801X, Vol. 28, no 1, p. 121-130Article in journal (Refereed) Published
Abstract [en]

Two alternating polyfluorenes (APFO15-F8BT and APFO3-F8BT) with full absorption of the visible region of the electromagnetic radiation were designed and synthesized for bulk-heterojunction solar cell devices. The optical and electrochemical properties of the two polymers were studied. The two polymers exhibited strong absorption in the visible region with no significant valley over the visible region extending up to 650 nm. Deep HOMO and ideally situated LUMO energy levels were the characteristics of the two polymers as revealed from the square wave voltammogram study: desired properties for extracting high open circuit voltage and for a facile charge transfer to the acceptor component in devices to take place, respectively. Photovoltaic devices were fabricated by blending the two polymers with PCBM[70] and up to similar to 2% power conversion efficiency were obtained.

Place, publisher, year, edition, pages
Chemical Society of Ethiopia, 2014
Keywords
Polyfluorenes; Bulk-heterojunction solar cells; Optical absorption; HOMO and LUMO
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-111761 (URN)10.4314/bcse.v28i1.14 (DOI)000342536400014 ()
Note

Funding Agencies|International Science Programme (ISP), Uppsala University, Sweden

Available from: 2014-10-31 Created: 2014-10-31 Last updated: 2017-12-05
Zhen, H., Hou, Q., Li, K., Ma, Z., Fabiano, S., Gao, F. & Zhang, F. (2014). Solution-processed bulk-heterojunction organic solar cells employing Ir complexes as electron donors. Journal of Materials Chemistry A, 2(31), 12390-12396
Open this publication in new window or tab >>Solution-processed bulk-heterojunction organic solar cells employing Ir complexes as electron donors
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2014 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 2, no 31, p. 12390-12396Article in journal (Refereed) Published
Abstract [en]

To explore enhancing photocurrent in organic solar cells (OSCs) via harvesting triplet excitons, two novel bicycloiridium complexes (R-1 and R-2) are designed and synthesized. Conventional bulk-heterojunction triplet OSCs are solution processed using R-1 or R-2 as sole electron donors and phenyl-C-71-butyric acid methyl ester (PC71BM) as the electron acceptor. A decent short circuit current (J(sc)) of 6.5 mA cm(-2) is achieved though the overlap between the absorption spectrum (with similar to 550 nm absorption onset) of R-2 and the solar flux is relatively small. With an open circuit voltage of 0.74 V and a fill factor of 0.42, an encouraging power conversion efficiency of 2.0% is achieved in the OSCs based on R-2 and PC71BM without any processing additives and post-treatments. Our preliminary result demonstrates the possibility of utilizing Ir complexes as sole electron donors in OSCs, which extends available soluble small molecules for OSCs.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2014
National Category
Biological Sciences Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-109603 (URN)10.1039/c4ta01526f (DOI)000339625500035 ()
Available from: 2014-08-21 Created: 2014-08-21 Last updated: 2017-12-05
Ma, Z., Sun, W., Himmelberger, S., Vandewal, K., Tang, Z., Bergqvist, J., . . . Wang, E. (2014). Structure-Property Relationships of Oligothiophene-Isoindigo Polymers for Efficient Bulk-Heterojunction Solar Cells. energy and environmental science, 17(1), 361-369
Open this publication in new window or tab >>Structure-Property Relationships of Oligothiophene-Isoindigo Polymers for Efficient Bulk-Heterojunction Solar Cells
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2014 (English)In: energy and environmental science, ISSN 1754-5692, Vol. 17, no 1, p. 361-369Article in journal (Refereed) Published
Abstract [en]

A series of alternating oligothiophene (nT)-isoindigo (I) copolymers (PnTI) were synthesized to investigate the influence of the oligothiophene block length on the photovoltaic (PV) properties of PnTI:PCBM bulk-heterojunction blends. Our study indicates that the number of thiophene rings (n) in the repeating unit alters both, polymer crystallinity and polymer-fullerene interfacial energetics, which results in a decreasing open-circuit voltage (Voc) of the solar cells with increasing n. The short-circuit current density (Jsc) of P1TI:PCBM devices is limited by the absence of a significant driving force for electron transfer. Instead, blends based on P5TI and P6TI feature large polymer domains, which limit charge generation and thus Jsc. The best PV performance with a power conversion efficiency of up to 6.9% was achieved with devices based on P3TI, where a combination of favorable morphology and optimal interface energy level offset ensures efficient exciton separation and charge generation. The structure-property relationship demonstrated in this work is a valuable guideline for the design of high performance polymers with small energy losses during the charge generation process, allowing for the fabrication of efficient solar cells that combine a minimal loss in Voc with a high Jsc.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2014
Keywords
organic solar cell, fullerene, conjugated polymer, charge transfer state
National Category
Natural Sciences Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-99424 (URN)10.1039/c3ee42989j (DOI)000329550700025 ()
Available from: 2013-10-17 Created: 2013-10-17 Last updated: 2015-05-29Bibliographically approved
Bergqvist, J., Lindqvist, C., Backe, O., Ma, Z., Tang, Z., Tress, W., . . . Müller, C. (2014). Sub-glass transition annealing enhances polymer solar cell performance. Journal of Materials Chemistry A, 2(17), 6146-6152
Open this publication in new window or tab >>Sub-glass transition annealing enhances polymer solar cell performance
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2014 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 2, no 17, p. 6146-6152Article in journal (Refereed) Published
Abstract [en]

Thermal annealing of non-crystalline polymer: fullerene blends typically results in a drastic decrease in solar cell performance. In particular aggressive annealing above the glass transition temperature results in a detrimental coarsening of the blend nanostructure. We demonstrate that mild annealing below the glass transition temperature is a viable avenue to control the nanostructure of a non-crystalline thiophene-quinoxaline copolymer: fullerene blend. Direct imaging methods indicate that coarsening of the blend nanostructure can be avoided. However, a combination of absorption and luminescence spectroscopy reveals that local changes in the polymer conformation as well as limited fullerene aggregation are permitted to occur. As a result, we are able to optimise the solar cell performance evenly across different positions of the coated area, which is a necessary criterion for large-scale, high throughput production.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2014
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-106302 (URN)10.1039/c3ta14165a (DOI)000333580700024 ()
Available from: 2014-05-06 Created: 2014-05-05 Last updated: 2015-12-03Bibliographically approved
Hou, Q., Chen, Y., Zhen, H., Ma, Z., Hong, W., Shi, G. & Zhang, F. (2013). A triphenylamine-based four-armed molecule for solution-processed organic solar cells with high photo-voltage. JOURNAL OF MATERIALS CHEMISTRY A, 1(16), 4937-4940
Open this publication in new window or tab >>A triphenylamine-based four-armed molecule for solution-processed organic solar cells with high photo-voltage
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2013 (English)In: JOURNAL OF MATERIALS CHEMISTRY A, ISSN 2050-7488, Vol. 1, no 16, p. 4937-4940Article in journal (Refereed) Published
Abstract [en]

A new four-armed molecule Th-4(DTPAB) with a triphenylamine-benzothiadiazole-triphenylamine unit as the core and 4-hexylthiophene as arms was synthesized. Solution-processed organic solar cells based on blends of Th-4(DTPAB) and PC71BM demonstrate a power conversion efficiency of 3.18% with a high open circuit voltage of 0.96 V.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-96518 (URN)10.1039/c3ta10401j (DOI)000316807100002 ()
Available from: 2013-08-21 Created: 2013-08-20 Last updated: 2013-08-21
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