| 1. |
- 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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| 2. |
- 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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| 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. |
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| 7. |
- Yu, Liyang, 1986, et al.
(författare)
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Diffusion-Limited Crystallization: A Rationale for the Thermal Stability of Non-Fullerene Solar Cells
- 2019
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Ingår i: ACS Applied Materials & Interfaces. - : American Chemical Society (ACS). - 1944-8252 .- 1944-8244.
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 American Chemical Society. Organic solar cells are thought to suffer from poor thermal stability of the active layer nanostructure, a common belief that is based on the extensive work that has been carried out on fullerene-based systems. We show that a widely studied non-fullerene acceptor, the indacenodithienothiophene-based acceptor ITIC, crystallizes in a profoundly different way as compared to fullerenes. Although fullerenes are frozen below the glass-transition temperature Tg of the photovoltaic blend, ITIC can undergo a glass-crystal transition considerably below its high Tg of ∼180 °C. Nanoscopic crystallites of a low-temperature polymorph are able to form through a diffusion-limited crystallization process. The resulting fine-grained nanostructure does not evolve further with time and hence is characterized by a high degree of thermal stability. Instead, above Tg, the low temperature polymorph melts, and micrometer-sized crystals of a high-temperature polymorph develop, enabled by more rapid diffusion and hence long-range mass transport. This leads to the same detrimental decrease in photovoltaic performance that is known to occur also in the case of fullerene-based blends. Besides explaining the superior thermal stability of non-fullerene blends at relatively high temperatures, our work introduces a new rationale for the design of bulk heterojunctions that is not based on the selection of high-Tg materials per se but diffusion-limited crystallization. The planar structure of ITIC and potentially other non-fullerene acceptors readily facilitates the desired glass-crystal transition, which constitutes a significant advantage over fullerenes, and may pave the way for truly stable organic solar cells.
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