| 1. |
- Gebremariam, Kidan G., et al.
(författare)
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Self-Assembled Monolayer Engineered ZnO Electron Transport Layer to Improve the Photostability of Organic Solar Cells
- 2024
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Ingår i: Energy & Fuels. - 1520-5029 .- 0887-0624. ; 38:14, s. 13304-13314
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Tidskriftsartikel (refereegranskat)abstract
- The degradation of organic solar cells (OSCs) can occur in any of the layers, underlining the importance of each layer in prolonging their lifetime. To enhance the performance and stability of inverted OSCs (i-OSCs), interfacial modification has been employed. In this context, two self-assembled monolayers (SAMs), namely, octadecanthiol (ODT) and octadecyltrimethoxysilane (OTMS), were utilized to effectively passivate typical surface defects in the ZnO electron transport layer (ETL). The SAM-treated ZnO films were found to be more hydrophobic, which reduced surface defects produced by adsorbed oxygen and hydroxyl groups. Consequently, the power conversion efficiency (PCE) of the i-OSCs comprising an indacenodithieno[3,2-b]thiophene-alt-5,5-di(thiophen-2-yl)-2,2-bithiazole (PIDTT-DTBTz) donor blended with [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) acceptor increased from 4.20% in pristine ZnO- to 5.01 and 5.37% in ODT- and OTMS-treated ZnO-based devices, respectively. In addition, the photostability of the device substantially improved. Hence, devices based on ZnO treated with ODT and OTMS kept 76 and 89% of their initial PCE, respectively, while pristine ZnO-based devices retained only 66% of the initial PCE after 48 h of irradiation. The improved PCE and extended lifetime of the i-OSCs can be attributed to enhanced charge transfer, the reduction in both bimolecular and trap-assisted recombination processes, and the enhanced interface between the ETL and the active layer. Moreover, it has been observed that the OTMS-treated ZnO ETL-based i-OSC offers better stability and more efficient devices compared to the ODT-treated ZnO ETL-based devices. This can be attributed to the favorable dipole moment generated by the increased electrostatic potential at the anchor group, which promotes improved device performance.
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| 2. |
- Genene, Zewdneh, 1983, et al.
(författare)
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Comparative study on the effects of alkylsilyl and alkylthio side chains on the performance of fullerene and non-fullerene polymer solar cells
- 2020
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Ingår i: Organic Electronics: physics, materials, applications. - : Elsevier BV. - 1566-1199. ; 77
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Tidskriftsartikel (refereegranskat)abstract
- Two novel high gap donor polymers – PBDTTSi-TzBI and PBDTTS-TzBI, based on imide-fused benzotriazole (TzBI) with asymmetric side chains and alkylsilyl (Si) or alkylthio (S) substituted 4,8-di(thien-2-yl)benzo-[1,2-b:4,5-b′]dithiophene (BDTT) – are successfully synthesized. The effect of the side chain variation on the photophysical, morphological and photovoltaic properties of blends of these polymers with fullerene and non-fullerene acceptors is investigated. The PBDTTSi-TzBI polymer shows a deeper highest occupied molecular orbital energy level, which results in higher open-circuit voltages. Nevertheless, the polymer solar cells fabricated using PBDTTS-TzBI in combination with PC71BM afford a higher power conversion efficiency of 7.3% (vs 4.0% for PBDTTSi-TzBI:PC71BM). By using the non-fullerene acceptor ITIC, the absorption of the blends extends to 850 nm and better device efficiencies are achieved, 6.9% and 9.6% for PBDTTSi-TzBI:ITIC and BDTTS-TzBI:ITIC, respectively. The better performance of the PBDTTS-TzBI:ITIC-based devices is attributed to the strong and broad absorption and balanced charge transport, and is among the best performances reported for non-fullerene solar cells based on TzBI-containing polymer donors.
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| 3. |
- Negash, Asfaw, et al.
(författare)
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Diketopyrrolopyrrole-based terpolymers with tunable broad band absorption for fullerene and fullerene-free polymer solar cells
- 2019
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7534 .- 2050-7526. ; 7:11, s. 3375-3384
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Tidskriftsartikel (refereegranskat)abstract
- A series of random terpolymers with donor-acceptor-donor-acceptor molecular configuration, comprising fluorinated benzotriazole (FTAZ) and thienothiophene-capped diketopyrrolopyrrole (TTDPP) as the first and second electron-accepting moieties and thienyl-substituted benzodithiophene (BDTT) as the electron-donating unit, are designed for polymer solar cells. By tuning the ratio of TTDPP and FTAZ, the optoelectronic properties of the terpolymers are systematically varied. All materials exhibit a broad absorption window spanning from 300 to 900 nm, illustrating the success of the terpolymer approach. Fullerene-based polymer solar cells fabricated from the terpolymer with the highest content of TTDPP afford a power conversion efficiency of 5.7%, with a short-circuit current density of 15.2 mA cm -2 . On the other hand, solar cell devices composed of the terpolymer with the lowest content of TTDPP and the narrow gap non-fullerene acceptor IEICO-4F exhibit a higher efficiency of 6.3%, with an enhanced short-circuit current density of 17.5 mA cm -2 , as a result of a better complementarity in the absorption of the donor and acceptor materials and well-balanced charge carrier mobilities. This efficiency represents the best value for fullerene-free polymer solar cells based on DPP-containing polymers to date.
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| 4. |
- Negash, Asfaw, et al.
(författare)
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Exploring the High-Temperature Window of Operation for Organic Photovoltaics: A Combined Experimental and Simulations Study
- 2024
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Ingår i: Advanced Materials for Optics and Electronics. - 1616-301X .- 1616-3028. ; 34:6
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Tidskriftsartikel (refereegranskat)abstract
- The global climate change negatively affects the photovoltaic performance of traditional solar cell technologies. This article investigates the potential of organic photovoltaics (OPV) for high-temperature environments, ranging from urban hot summers (30—40 °C) and desert regions (65 °C) up to (aero) space conditions (130 °C), the thermal window in which OPV can operate. The approach is based on a combination of experiments and simulations up to 180 °C, moving significantly beyond the conventional temperature ranges reported in the literature. New 2H-benzo[d][1,2,3]triazole-5,6-dicarboxylic imide-based copolymers with decomposition onset temperatures above 340 °C are used for this study, in combination with non-fullerene acceptors. Contrary to their inorganic counterparts, OPV devices show a positive temperature coefficient up to ≈90 °C. At temperatures of 150 °C, they are still operational, retaining their room temperature efficiency. Complementary simulations are performed using an in-house developed software package that numerically solves the drift-diffusion equations to understand the general trends in the obtained current–voltage characteristics and the materials’ intrinsic behavior as a function of temperature. The presented methodology of combined high-temperature experiments and simulations can be further applied to investigate the thermal window of operation for other OPV material systems, opening novel high-temperature application routes.
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| 5. |
- Negash, Asfaw, et al.
(författare)
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Ladder-type high gap conjugated polymers based on indacenodithieno[3,2-b]thiophene and bithiazole for organic photovoltaics
- 2019
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Ingår i: Organic Electronics: physics, materials, applications. - : Elsevier BV. - 1566-1199. ; 74, s. 211-217
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 Elsevier B.V. Two push-pull type conjugated polymers - PIDTT−BTz and PIDTT−DTBTz, based on the ladder-type donor unit indacenodithieno[3,2-b]thiophene (IDTT) and bithiazole (BTz) as acceptor component - are designed and synthesized for photovoltaic applications. The polymers exhibit relatively high optical gaps of ~2.0 eV with strong absorption in the range of 400–600 nm, rendering them of particular interest for the harvesting of indoor light and/or multijunction devices. Electrochemical investigations indicate a lower highest occupied molecular orbital energy level (−5.44 eV) for PIDTT−BTz as compared to PIDTT−DTBTz (−5.36 eV), enabling to achieve a higher open-circuit voltage. Under solar illumination, the best power conversion efficiency (5.1%) is achieved for the combination PIDTT−DTBTz:PC71BM (compared to 4.6% for PIDTT−BTz:PC71BM).
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| 6. |
- Tegegne, Newayemedhin A., et al.
(författare)
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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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Ingår i: Materials Advances. - 2633-5409. ; 4:24, s. 6694-6703
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Tidskriftsartikel (refereegranskat)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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