| 1. |
- Jalan, Ishita, 1991-, et al.
(author)
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Donor-acceptor polymer complex formation in solution confirmed by spectroscopy and atomic-scale modelling
- 2023
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In: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 11:27, s. 9316-9326
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Journal article (peer-reviewed)abstract
- In all-polymer solar cells, high performance is attributed to the fine-grained morphology of the film in the active layer. However, the mechanism by which this fine-grained morphology is achieved remains unknown. Polymeric non-fullerene acceptors have the potential to restrict the self-aggregation, typical of non-fullerene small molecule acceptors. Here we employed a blend of the polymeric acceptor PF5-Y5 and the donor polymer PBDB-T to investigate the balance between molecular interactions in solution. Temperature-dependent absorption spectra show evidence of temperature-induced disaggregation of both donor and acceptor polymers, where the donor polymer disaggregation depends on the solvent polarity. Concentration-dependent fluorescence spectra of blend solutions display blue-shifted acceptor emission upon dilution, similar to that observed in acceptor solutions, and a decreased tendency for charge transfer from donor to acceptor upon dilution. Excitation spectra of dilute blend solutions contain an increased contribution to the long-wavelength acceptor emission, as compared to pure acceptor solutions, from a chromophore that absorbs in a region where the donor does not absorb. These observations can be explained by donor-acceptor complexation in dilute blend solutions, that is stabilized in more polar solvents. Moreover, the near IR-region of the absorption spectrum could be matched with the calculated electronic excitations of donor-acceptor complexes of PBDB-T and PF5-Y5 oligomers. The results corroborate that the interaction between segments of the donor and acceptor polymer chains favours the formation of donor-acceptor charge transfer complexes, stabilized by hybridization of the molecular orbitals, which reduces the electronic energy. The proposed donor-acceptor complex formation competes with the donor and acceptor self-aggregation and is influenced by the solvent environment. These pre-formed donor-acceptor complexes in low-concentration solutions can be expected to have important consequences on the film morphology of all-polymer blends. The results from this joint experimental-theoretical spectroscopy study provide insights that can guide the design of compatible donor and acceptor polymers for future high-performance organic solar cells.
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| 2. |
- Prasad, Suraj, et al.
(author)
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Photostability of Y-type electron acceptor molecules and related copolymer
- 2023
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In: Proceedings Volume 12660, Organic, Hybrid, and Perovskite Photovoltaics XXIV. - : SPIE - The International Society for Optics and Photonics. ; 12660
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Conference paper (peer-reviewed)abstract
- The lifetime of organic solar cells critically depends on the photochemical stability of the materials. To shed light on the photostability of novel Y-series electron acceptors, we investigate the evolution of optical properties and composition during one-sun illumination in ambient atmosphere of thin films of the small-molecule acceptor Y5 and its copolymers PF5-Y5 and PYT. We employ UV-vis, Fourier-transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS), to assess changes in these properties as a function of illumination time. UV-Vis spectra show that PF5-Y5 undergoes rapid photobleaching, while the Y5 spectrum remains essentially unaffected even after 30 hours of exposure. The absorption spectrum of PYT, which contains a different co-mer than PF5-Y5, is only weakly affected. XPS C1s spectra of the PF5- Y5 film show a decreasing main peak and the development of a new component after 30 hours exposure, while the Y5 film surface composition remained intact. The photodegradation products of PF5-Y5 are characterized by the presence of new carbonyl groups, emerging as absorption bands in the FTIR spectra, while such spectral changes are absent for the Y5 film, indicating that Y5 is resistant to photooxidation, while PF5-Y5 undergoes photochemical reactions. The faster photodegradation of PF5-Y5 compared to Y5 and PYT raises the question about the role of the copolymer’s BDT moiety in the photooxidation. These new insights on the dependence of the photostability of acceptor molecules on their molecular structure are expected to contribute to the design of stable acceptor copolymers for organic solar cells with long operational lifetimes.
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| 3. |
- Tegegne, Newayemedhin A., et al.
(author)
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Tailoring intra-molecular coupling in BDT-based copolymers to enhance their performance in fullerene-free organic solar cells
- 2023
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In: Materials Advances. - 2633-5409. ; 4:24, s. 6694-6703
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Journal article (peer-reviewed)abstract
- Three copolymers based on a 4,8-bis(4,5-dioctylthiophen-2-yl)benzo[1,2-b:4,5-b ']dithiophene (BDTT) donor unit coupled with 6-(2-ethylhexyl)-5H-[1,2,5]thiadiazolo[3,4-f]isoindole-5,7(6H)-dione (P1), 6-octyl-4,8-di(thiophen-2-yl)-5H-[1,2,5]thiadiazolo[3,4-f]isoindole-5,7(6H)-dione (P2) and 2-(2-ethylhexyl)-6-octyl-4,8-di(thiophen-2-yl)-[1,2,3]triazolo[4,5-f]isoindole-5,7(2H,6H)-dione (P3) acceptors were computationally designed and experimentally synthesized to tailor the intramolecular coupling in their backbone. A considerable decrease in distortion energy in P2 compared to P1 proved the major role of the pi-spacer in the copolymer in releasing steric strain. In comparison to the [1,2,3]triazolo[4,5-f]isoindole-5,7(2H,6H)-dione-based copolymer, P3, the lower electrostatic potential (ESP) of the [1,2,5]thiadiazolo[3,4-f]isoindole-5,7(6H)-dione acceptor in P1 has been observed to shift its LUMO energy level by about 0.5 eV. Furthermore, the electron donating properties of the copolymers increased in the order of P1 < P2 < P3 due to the synergistic contribution of each unit rather than a single unit, confirming the importance of tailoring the intramolecular coupling to control the electro-optical properties of the copolymers. Finally, the copolymer with a poorer electron acceptor unit (P3) was found to exhibit complementary absorption with the non-fullerene acceptor, ITIC, yielding a PCE of 8.87% in solar cell devices, further demonstrating the relevance of each unit in the copolymer intramolecular coupling.
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| 4. |
- Waketola, Alemayehu G., et al.
(author)
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Embedding plasmonic gold nanoparticles in a ZnO layer enhanced the performance of inverted organic solar cells based on an indacenodithieno[3,2-b]thiophene-alt-5,5'-di(thiophen-2-yl)-2,2'-bithiazole-based push-pull polymer
- 2023
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In: RSC Advances. - 2046-2069. ; 13:24, s. 16175-16184
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Journal article (peer-reviewed)abstract
- Recently, plasmonic nanoparticles (NPs) have attracted considerable attention as good candidates for enhancing the power conversion efficiency (PCE) of organic solar cells (OSCs) owing to their localized surface plasmon resonance (LSPR). In this study, the effect of embedding colloidal gold nanoparticles (cAu NPs) in the ZnO electron transport layer (ETL) on the PCEs of wide band gap polymer-based inverted OSCs was investigated. The active layer was composed of a bulk heterojunction of conjugated polymer based on indacenodithieno[3,2-b]thiophene and 5,5'-di(thiophen-2-yl)-2,2'-bithiazole PIDTT-DTBTz as a donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as an acceptor. The PCE of the reference device was improved by 22% when 10 wt% cAu NPs were embedded in the ZnO ETL. The short circuit current density (J(SC)) and fill factor (FF) were the main photovoltaic parameters contributing to the PCE enhancement. An improved absorption in the active layer due to the LSPR of cAu NPs as well as efficient exciton dissociation and charge collection were found to be the reasons for the enhanced J(SC) while the increase in FF was mainly due to the suppressed traps and improved conductivity of the ZnO layer by the NPs.
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| 5. |
- Waketola, Alemayehu G., et al.
(author)
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Enhancing the Performance of Wide-Bandgap Polymer-Based Organic Solar Cells through Silver Nanorod Integration
- 2023
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In: ACS Omega. - 2470-1343. ; In Press
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Journal article (peer-reviewed)abstract
- Light trapping induced by the introduction of metallic nanoparticles has been shown to improve photo absorption in organic solar cells (OSCs). Researchers in the fields of plasmonics and organic photovoltaics work together to boost sunlight absorption and photon-electron interactions in order to improve device performance. In this contribution, an inverted OSC was fabricated by using indacenodithieno[3,2-b]thiophene-alt-2,2′-bithiazole (PIDTT-BTz) as a wide-band gap donor copolymer and (6,6)-phenyl-C71-butyric acid methyl ester (PC71BM) as an acceptor. Silver nanorods (Ag-NRs), synthesized by precipitation method, were embedded in the active layer of the solar cell. The device fabricated with 1 wt % Ag-NRs in the active layer showed a 26% improvement in power conversion efficiency (PCE) when exposed to 100 mW/cm2 simulated solar illumination. The role of Ag-NRs in the performance improvement of the OSCs was analyzed systematically using morphological, electrical, and optical characterization methods. The light trapping and exciton generation were improved due to the localized surface plasmon resonance (LSPR) activated in Ag-NRs in the form of longitudinal and transverse modes. The photoactive layers (PIDTT-BTz:PC71BM) with the incorporation of 0.5 and 1 wt % Ag-NR showed increased absorption, while the absorption with 1.5 wt % Ag-NRs appeared to be reduced in the wavelength range from 400 to 580 nm. Ag-NRs play a favorable role in exciton photogeneration and dissociation due to the two LSPR modes generated by the Ag-NRs. In the optimized device, the short-circuit current density (JSC) increased from 11.92 to 14.25 mA/cm2, resulting in an increase in the PCE from 3.94 to 4.93%, which is attributed to the improved light-trapping by LSPR using Ag-NRs.
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| 6. |
- Wu, Jingnan, 1994, et al.
(author)
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On the Conformation of Dimeric Acceptors and Their Polymer Solar Cells with Efficiency over 18 %
- 2023
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In: Angewandte Chemie International Edition. - : John Wiley & Sons. - 1433-7851 .- 1521-3773. ; 62:45
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Journal article (peer-reviewed)abstract
- The determination of molecular conformations of oligomeric acceptors (OAs) and their impact on molecular packing are crucial for understanding the photovoltaic performance of their resulting polymer solar cells (PSCs) but have not been well studied yet. Herein, we synthesized two dimeric acceptor materials, DIBP3F-Se and DIBP3F-S, which bridged two segments of Y6-derivatives by selenophene and thiophene, respectively. Theoretical simulation and experimental 1D and 2D NMR spectroscopic studies prove that both dimers exhibit O-shaped conformations other than S- or U-shaped counter-ones. Notably, this O-shaped conformation is likely governed by a distinctive "conformational lock" mechanism, arising from the intensified intramolecular & pi;-& pi; interactions among their two terminal groups within the dimers. PSCs based on DIBP3F-Se deliver a maximum efficiency of 18.09 %, outperforming DIBP3F-S-based cells (16.11 %) and ranking among the highest efficiencies for OA-based PSCs. This work demonstrates a facile method to obtain OA conformations and highlights the potential of dimeric acceptors for high-performance PSCs.
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| 7. |
- Yao, Nannan, et al.
(author)
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In Situ Study the Dynamics of Blade-Coated All-Polymer Bulk Heterojunction Formation and Impact on Photovoltaic Performance of Solar Cells
- 2023
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In: Solar RRL. - : John Wiley & Sons. - 2367-198X. ; , s. 1-8
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Journal article (peer-reviewed)abstract
- All-polymer solar cells (all-PSCs) have achieved impressive progress by employing acceptors polymerized from well performing small-molecule non-fullerene acceptors. Herein, the device performance and morphology evolution in blade-coated all-PSCs based on PBDBT:PF5–Y5 blends prepared from two different solvents, chlorobenzene (CB), and ortho-xylene (o-XY) are studied. The absorption spectra in CB solution indicate more ordered conformation for PF5–Y5. The drying process of PBDBT:PF5–Y5 blends is monitored by in situ multifunctional spectroscopy and the final film morphology is characterized with ex situ techniques. Finer-mixed donor/acceptor nanostructures are obtained in CB-cast film than that in o-XY-cast ones, corresponding to more efficient charge generation in the solar cells. More importantly, the conformation of polymers in solution determines the overall film morphology and the device performance. The relatively more ordered structure in CB-cast films is beneficial for charge transport and reduced non-radiative energy loss. Therefore, to achieve high-performance all-PSCs with small energy loss, it is crucial to gain favorable aggregation in the initial stage in solution.
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