| 1. |
- Cai, Wanzhu, et al.
(författare)
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Self-doped conjugated polyelectrolyte with tuneable work function for effective hole transport in polymer solar cells
- 2016
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 4:40, s. 15670-15675
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Tidskriftsartikel (refereegranskat)abstract
- A water-soluble conjugated polyelectrolyte (CPE), PEDOT-S (poly(4-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl-methoxy)-1-butanesulfonic acid)), is demonstrated to be an excellent hole transport material in several polymer solar cells with different donor's HOMO (highest occupied molecular orbital). With a P3TI:PC71BM (poly[6,6′-bis(5′-bromo-3,4′-dioctyl-[2,2′-bithiophen]-5-yl)-1,1′-bis(2-hexyldecyl)-[3,3′-biindolinylidene]-2,2′-dione]:[6,6]-phenyl C71 butyric acid methyl ester) active layer, the device using PEDOT-S as a hole transport layer (HTL) outperforms the PEDOT:PSS-based devices due to an increased FF (fill factor). The devices' current density–voltage characteristics (J–V) show that a PEDOT-S layer can operate well with a wide range of thicknesses as well, helped by its high conductivity and decent transparency. With UV-ozone treatment, the work function of the PEDOT-S can increase from 4.9 eV to 5.2 eV. In TQ1:PC71BM (poly[[2,3-bis(3-octyloxyphenyl)-5,8-quinoxalinediyl]-2,5-thiophenediyl]:PC71BM) devices, which have a deeper donor HOMO than P3TI, Voc is improved from 0.81 V to 0.92 V by 7 min UV-ozone treatment, along with a suppressed reverse injection current and increased Jsc (short-circuit current density) and FF. Topography study shows the excellent coating ability of PEDOT-S. Conductive atomic force microscopy (C-AFM) shows the out-of-plane current in PEDOT-S film is one thousand times higher than that in PEDOT:PSS PH 4083 film under the same electric field and has much more uniformly distributed current pathways.
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| 2. |
- Gedefaw, Desta Antenehe, 1971, et al.
(författare)
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An alternating copolymer of fluorene donor and quinoxaline acceptor versus a terpolymer consisting of fluorene, quinoxaline and benzothiadiazole building units: synthesis and characterization
- 2016
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Ingår i: Polymer Bulletin. - : Springer Science and Business Media LLC. - 0170-0839 .- 1436-2449. ; 73:4, s. 1167-1183
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Qian, D. P., et al.
(författare)
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Modulating molecular aggregation by facile heteroatom substitution of diketopyrrolopyrrole based small molecules for efficient organic solar cells
- 2015
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 3:48, s. 24349-24357
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Bai, Sai, et al.
(författare)
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Ethanedithiol Treatment of Solution-Processed ZnO Thin Films: Controlling the Intragap States of Electron Transporting Interlayers for Efficient and Stable Inverted Organic Photovoltaics
- 2015
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Ingår i: Advanced Energy Materials. - : Wiley-VCH Verlag. - 1614-6832 .- 1614-6840. ; 5:5, s. 1401606-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Bergqvist, Jonas, et al.
(författare)
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Sub-glass transition annealing enhances polymer solar cell performance
- 2014
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488. ; 2:17, s. 6146-6152
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Du, Chun, et al.
(författare)
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9-Alkylidene-9H-Fluorene-Containing Polymer for High-Efficiency Polymer Solar Cells
- 2011
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Ingår i: Macromolecules. - : American Chemical Society. - 0024-9297 .- 1520-5835. ; 44:19, s. 7617-7624
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Tidskriftsartikel (refereegranskat)abstract
- A novel donor-acceptor copolymer containing 9-alkylidene-9H-fluorene unit in the main chain, poly[9-(1-hexylheptylidene)-2,7-fluorene-alt-5, 5-(4,7-di-2-thienyl-5,6-dialkoxy-2,1,3-benzothiadiazole)] (PAFDTBT), has been synthesized and evaluated in bulk heterojunction polymer solar cells (BHJ PSCs). The polymer possesses a low band gap of 1.84 eV, a low-lying HOMO energy level (5.32 eV), and excellent solubility in common organic solvents. PSCs based on PAFDTBT and (6,6)-phenyl-C(71)-butyric add methyl ester (PC(71)BM) demonstrate a power conversion efficiency (PCE) of 6.2% with a high fill factor (FF) of 0.70, which indicates that 9-alkylidene-9H-fluorene can be a very useful building block for constructing narrow band gap conjugated polymers for high-efficiency BHJ PSCs.
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| 7. |
- Gedefaw, Desta Antenehe, 1971, et al.
(författare)
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Conjugated polymers with polar side chains in bulk heterojunction solar cell devices
- 2014
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Ingår i: Polymer International. - : Wiley. - 1097-0126 .- 0959-8103. ; 63:1, s. 22-30
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Tidskriftsartikel (refereegranskat)abstract
- 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. (c) 2013 Society of Chemical Industry
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| 8. |
- Gedefaw, Desta Antenehe, 1971, et al.
(författare)
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Random polyfluorene co-polymers designed for a better optical absorption coverage of the visible region of the electromagnetic spectrum
- 2014
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Ingår i: Bulletin of the Chemical Society of Ethiopia. - : African Journals Online (AJOL). - 1726-801X .- 1011-3924. ; 28:1, s. 121-130
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Hou, Qiong, et al.
(författare)
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A triphenylamine-based four-armed molecule for solution-processed organic solar cells with high photo-voltage
- 2013
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Ingår i: JOURNAL OF MATERIALS CHEMISTRY A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 1:16, s. 4937-4940
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Jiang, Sheng, et al.
(författare)
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In Situ Reconstruction of Hole-Selective Perovskite Heterojunction with Graded Energetics Toward Highly Efficient and Stable Solar Cells
- 2023
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Ingår i: Advanced Energy Materials. - : WILEY-V C H VERLAG GMBH. - 1614-6832 .- 1614-6840. ; 13:27
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Tidskriftsartikel (refereegranskat)abstract
- Perovskite solar cells (PSCs) have demonstrated a high power conversion efficiency, however, the large energy loss due to non-radiative recombination is the main challenge for further performance enhancement. Here, a surface treatment strategy is developed by heat-induced decomposition of a thin interlayer 2,7-Naphthaleneditriflate (NAP) to in situ reconstruct perovskite energetics. It is verified that the reconstructed perovskite surface energetics match better with the upper hole transport layer compared to the intrinsic condition. Spontaneous generation of n/n(-) homojunctions between the perovskite film bulk and the surface region promotes hole extraction, enhancing built-in electric field, and thus significantly suppresses charge recombination at such perovskite hole-selective heterojunctions. Moreover, the surface decomposed fluorine-rich complexes passivate the defects and improve the crystallinity of the perovskite film. These advantages are confirmed by a remarkably improved efficiency from 20.52% for the control device to 23.37% for the treated one with excellent stability. The work provides a promising approach of in situ reconstructing perovskite surface and interface for the design of highly efficient and stable PSCs.
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