| 101. |
- Liu, Jian, et al.
(författare)
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Printable highly conductive conjugated polymer sensitized ZnO NCs as cathode interfacial layer for efficient polymer solar cells
- 2014
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 6:11, s. 8237-8245
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Tidskriftsartikel (refereegranskat)abstract
- We report a facile way to produce printable highly conductive cathode interfacial layer (CIL) for efficient polymer solar cells (PSCs) by sensitizing ZnO nanocrystals (NCs) with a blue fluorescent conjugated polymer, poly(9, 9-bis-(6-diethoxylphosphorylhexyl) fluorene) (PFEP). Herein, PFEP plays dual distinctive roles in the composite. Firstly, PFEP chains can effectively block the aggregation of ZnO NCs, leading to uniform and smooth film during solution processing via assembly on ZnO NC surfaces through their pending phosphonate groups. Secondly, PFEP can greatly improve the conductivity of ZnO NCs by charge transfer doping, that is the charge transfer from the sensitizer driven by electron-chemical potential equilibrium, which could be even more pronounced under light illumination because of light excitation of PFEP sensitizer. The increased conductivity in ZnO-PFEP layer renders more efficient electron transport and extraction compared to pristine ZnO layer. This ZnO-PFEP CIL was successfully applied to PSCs based on three polymer donor systems with different band-gaps, and efficiency enhancements from 44 to 70% were observed compared to those PSCs with pristine ZnO CIL. The highest efficiency of 7.56% was achieved in P(IID-DTC):PC70BM-based PSCs by using ZnO-PFEP film as CIL. Moreover, the enhanced conductivity due to the charge-transfer doping effect allows thick ZnO-PFEP film to be used as CIL in high-performance PSCs. Both the high conductivity and good film-forming properties of ZnO-PFEP CIL are favorable for large-scale printable PSCs, which is also verified by high-efficiency PSCs with ZnO-PFEP CIL fabricated using doctor-blading, a large-scale processing technique. The work provides an efficient printable cathode interfacial material for efficient PSCs.
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| 102. |
- Liu, Yanfeng, et al.
(författare)
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In Situ Optical Spectroscopy Demonstrates the Effect of Solvent Additive in the Formation of All-Polymer Solar Cells
- 2022
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185 .- 1948-7185. ; 13:50, s. 11696-11702
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Tidskriftsartikel (refereegranskat)abstract
- 1-Chloronaphthalene (CN) has been a common solvent additive in both fullerene- A nd nonfullerene-based organic solar cells. In spite of this, its working mechanism is seldom investigated, in particular, during the drying process of bulk heterojunctions composed of a donor:acceptor mixture. In this work, the role of CN in all-polymer solar cells is investigated by in situ spectroscopies and ex situ characterization of blade-coated PBDB-T:PF5-Y5 blends. Our results suggest that the added CN promotes self-aggregation of polymer donor PBDB-T during the drying process of the blend film, resulting in enhanced crystallinity and hole mobility, which contribute to the increased fill factor and improved performance of PBDB-T:PF5-Y5 solar cells. Besides, the nonradiative energy loss of the corresponding device is also reduced by the addition of CN, corresponding to a slightly increased open-circuit voltage. Overall, our observations deepen our understanding of the drying dynamics, which may guide further development of all-polymer solar cells.
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| 103. |
- Liu, Yanfeng, et al.
(författare)
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Mo1.33C MXene-Assisted PEDOT:PSS Hole Transport Layer for High-Performance Bulk-Heterojunction Polymer Solar Cells
- 2020
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Ingår i: ACS APPLIED ELECTRONIC MATERIALS. - : AMER CHEMICAL SOC. - 2637-6113. ; 2:1, s. 163-169
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Tidskriftsartikel (refereegranskat)abstract
- Here, we report the usage of two-dimensional MXene, Mo1.33C-assisted poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as an efficient hole transport layer (HTL) to construct high-efficiency polymer solar cells. The composite HTLs are prepared by mixing Mo1.33C and PEDOT:PSS aqueous solution. The conventional devices based on Mo1.33C:PEDOT:PSS exhibit an average power conversion efficiency (PCE) of 9.2%, which shows a 13% enhancement compared to the reference devices. According to the results from hole mobilities, charge extraction probabilities, steady-state photoluminescence, and atomic force microscopy, the enhanced PCE can be ascribed to the improved charge transport and extraction properties of the HTL, along with the morphological improvement of the active layer on top. This work clearly demonstrates the feasibility to combine advantages of Mo1.33C MXene and PEDOT:PSS as the promising HTL in organic photovoltaics.
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| 104. |
- Liu, Yanfeng, 1992-
(författare)
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Studying Morphology Formation and Charge Separation in Organic Solar Cells
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We are currently living in the era of automation and artificial intelligence, which requires more energy than ever before. Meanwhile, the reduction of carbon footprint is needed for keeping the environment sustainable. Exploring green energy is crucial. Solar power is one of the green energy sources. The apparatus that converts solar energy to electricity is a solar cell. Organic solar cells (OSCs), employing organic materials absorbing solar radiation and converting to electricity have got extensive attention in the last decades due to their unique advantages like lightweight, semi-transparency, and potential industrialization. In most cases, an OSC composes of two different organic semiconductors as electron donor and acceptor to form a photoactive layer with a bulk heterojunction (BHJ) structure, and sandwiched between the electron and hole transport layers and then two electrodes. The morphology of the BHJ plays a crucial role in the device's performance, and it is a result of a complicated interplay between donor, acceptor, and solvent during the film drying from a solution. Thus, in-situ monitoring the film drying during solvent evaporation could deepen understanding of the mechanism of the morphology formation. A versatile multiple spectroscopic setup is assembled for this purpose, which can record laser scattering, steady-state photoluminescence (PL), time-resolved photoluminescence (TRPL), and white-light absorption during film formation. By comparing the drying dynamics of three different blend systems with their corresponding pristine films, we find that the blend film formation and its final morphology are more dominated by the component with a higher molecular weight. Different PL and TRPL quenching profiles between fullerene- and non-fullerene-based systems provide hints about different donor-acceptor interactions. Moreover, with the help of TRPL, the relative change of quantum yield during film formation can be calculated. Besides, this setup is also proved suitable for studying mechanisms behind device optimization processes, like the usage of solvent additives. One of the unique features of OSCs based on non-fullerene acceptors is the highly efficient hole transfer from the acceptor to the donor, sometimes even under zero or negative energetic offsets. However, in these cases the mechanism of hole transfer has not been fully understood. By studying hole transfer at the donor:acceptor interface in different material systems and device configurations, we highlight the role of electric field on the charge separation of OSCs when energetic offsets are not enough. To achieve better device performance, engineering the photoelectric properties of interfacial layers is equally essential. A good interfacial layer can facilitate carrier extraction and reduce carrier recombination. We demonstrate that adding MXenes into the PEDOT:PSS can increase the conductivity of this composite hole transport layer, without sacrificing its optical transparency and work function.
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| 105. |
- Ma, Chunyu, et al.
(författare)
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Plasmon-enhanced organic solar cells with solution-processed three-dimensional Ag nanosheets
- 2013
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Ingår i: Solar Energy Materials and Solar Cells. - : ELSEVIER SCIENCE BV, PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS. - 0927-0248 .- 1879-3398. ; 109, s. 227-232
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Tidskriftsartikel (refereegranskat)abstract
- The silver nanosheets (AgNSs) prepared via normal silver mirror reaction were used to improve the performance of organic solar cells. AgNSs with a size of about 100 nm in width and 10 nm in thickness formed a 3-D network on an indium tin oxide (ITO) surface. Organic solar cells with a structure of ITO/AgNSs/poly(3,4-ethylene dioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)/poly(3-hexylthiophene) and [6,6]-phenyl C-61 butyric acid methyl ester (P3HT:PC61BM)/LiF/Al exhibited an open circuit voltage (V-oc) of 0.60 +/- 0.01 V, short circuit current density (J(sc)) of 11.16 +/- 0.08 mA/cm(2), a fill factor (FF) of 53.69 +/- 0.92%, and power conversion efficiency (PCE) of 3.60 +/- 0.06%. The PCEs of organic solar cells with 3-D AgNSs layers were 1.29 times that of the control device without 3-D AgNSs layer. We attributed the improvement of the efficiency to localized surface plasmon resonance (LSPR) induced by the 3-D network of AgNSs, which enhanced the light harvest of active layers, increased the probability of exciton generation and dissociation.
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| 106. |
- Ma, Zaifei, et al.
(författare)
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A Facile Method to Enhance Photovoltaic Performance of Benzodithiophene-Isoindigo Polymers by Inserting Bithiophene Spacer
- 2014
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Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6840 .- 1614-6832. ; 4:6, s. Art. no. 1301455-
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Tidskriftsartikel (refereegranskat)abstract
- This study describes the synthesis and characterization of four polymers based on benzo[1,2-b:4,5-b']dithiophene (BDT) and isoindigo with zero, one, two, and three thiophene spacer groups. Results have demonstrated that the use of bithiophene as a spacer unit improves the geometry of the polymer chain, making it planar, and hence, potentially enhanced π- π stacking occurs. Due to favorable interaction of the polymer chains, enhanced absorption coefficient, and optimal morphology, PBDT-BTI, which possesses bithiophene as a spacer, revealed high current and fill factor leading to a power conversion efficiency of 7.3% in devices, making this polymer the best performing isoindigo-based material in polymer solar cells (PSCs). Also, PBDT-BTI could still maintain efficiency of over 6% with the active layer thickness of 270 nm, making it a potential candidate for a material in printed PSCs. These results demonstrate that the use of thiophene spacers in D-A polymers could be an important design strategy to produce high-performance PSCs.
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| 107. |
- Ma, Zaifei, et al.
(författare)
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Enhance performance of organic solar cells based on an isoindigo-based copolymer by balancing absorption and miscibility of electron acceptor
- 2011
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 99:14
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Tidskriftsartikel (refereegranskat)abstract
- Superior absorption of PC(71)BM in visible region to that of PC(61)BM makes PC(71)BM a predominant acceptor for most high efficient polymer solar cells (PSCs). However, we will demonstrate that power conversion efficiencies (PCEs) of PSCs based on poly[N,N'-bis(2-hexyldecyl)isoindigo-6, 6'-diyl-alt-thiophene-2,5-diyl] (PTI-1) with PC(61)BM as acceptor are 50% higher than their PC71BM counterparts under illumination of AM1.5G. AFM images reveal different topographies of the blends between PTI-1:PC(61)BM and PTI-1:PC(71)BM, which suggests that acceptor's miscibility plays a more important role than absorption. The photocurrent of 9.1 mA/cm(2) is among the highest value in PSCs with a driving force for exciton dissociation less than 0.2 eV.
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| 108. |
- Ma, Z. F., et al.
(författare)
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Structure-Property Relationships of Oligothiophene-Isoindigo Polymers for Efficient Bulk-Heterojunction Solar Cells
- 2014
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Ingår i: Energy and Environmental Sciences. - 1754-5692 .- 1754-5706. ; 7:1, s. 361-369
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Tidskriftsartikel (refereegranskat)abstract
- 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 a favorable morphology and an optimal interfacial energy level offset ensures efficient exciton separation and charge generation. The structure–property relationship demonstrated in this work would be 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.
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| 109. |
- Ma, Zaifei, et al.
(författare)
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Influences of Surface Roughness of ZnO Electron Transport Layer on the Photovoltaic Performance of Organic Inverted Solar Cells
- 2012
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:46, s. 24462-24468
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Tidskriftsartikel (refereegranskat)abstract
- Here, we demonstrate the correlation between the surface roughness of the ZnO interlayer used as an electron transporting interlayer (ETL) in organic inverted solar cells (ISCs) and the photovoltaic performance of the ISCs. Three different surfaces of the ZnO ETL are studied in ISCs with the polymer poly[2,3-bis-(3-octyloxyphenyl)-quinoxaline-5,8-diyl-alt-thiophene-2,5-d iyl] (TQ1) mixed with [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) as the active layer. The results obtained from these ISCs show that power conversion efficiency increases from 2.7% to 3.9% when the root-mean-square roughness of the ZnO layer decreases from 48 to 1.9 nm. Moreover, it is found that the short-circuit current density is higher in the ISC based on the smoother ZnO interlayer, with a larger donor/acceptor (D/A) interfacial area in the active layer that facilitates exciton dissociation. The reduced effective interfacial area between the photoactive layer and the ZnO interlayer with decreased ZnO surface roughness leads to an observed improvement in both fill factor and open circuit voltage, which is ascribed to a reduced concentration of traps at the interface between the ZnO interlayer and the active layer.
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| 110. |
- Ma, Zaifei, et al.
(författare)
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Structure-Property Relationships of Oligothiophene-Isoindigo Polymers for Efficient Bulk-Heterojunction Solar Cells
- 2014
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Ingår i: energy and environmental science. - : Royal Society of Chemistry. - 1754-5692. ; 17:1, s. 361-369
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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