| 1. |
- Chen, Xian-Kai, et al.
(författare)
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A unified description of non-radiative voltage losses in organic solar cells
- 2021
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Ingår i: Nature Energy. - : Springer Nature. - 2058-7546. ; 6:8, s. 799-806
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Tidskriftsartikel (refereegranskat)abstract
- Organic solar cells based on non-fullerene acceptors have enabled high efficiencies yet their charge dynamics and its impact on the photovoltaic parameters are not fully understood. Now, Chen et al. provide a general description of non-radiative voltage losses in both fullerene and non-fullerene solar cells. Recent advances in organic solar cells based on non-fullerene acceptors (NFAs) come with reduced non-radiative voltage losses (Delta V-nr). Here we show that, in contrast to the energy-gap-law dependence observed in conventional donor:fullerene blends, the Delta V-nr values in state-of-the-art donor:NFA organic solar cells show no correlation with the energies of charge-transfer electronic states at donor:acceptor interfaces. By combining temperature-dependent electroluminescence experiments and dynamic vibronic simulations, we provide a unified description of Delta V-nr for both fullerene- and NFA-based devices. We highlight the critical role that the thermal population of local exciton states plays in low-Delta V-nr systems. An important finding is that the photoluminescence yield of the pristine materials defines the lower limit of Delta V-nr. We also demonstrate that the reduction in Delta V-nr (for example, <0.2 V) can be obtained without sacrificing charge generation efficiency. Our work suggests designing donor and acceptor materials with high luminescence efficiency and complementary optical absorption bands extending into the near-infrared region.
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| 2. |
- Gillett, Alexander J., et al.
(författare)
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The role of charge recombination to triplet excitons in organic solar cells
- 2021
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Ingår i: Nature. - : NATURE PORTFOLIO. - 0028-0836 .- 1476-4687. ; 597:7878, s. 666-
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Tidskriftsartikel (refereegranskat)abstract
- The use of non-fullerene acceptors (NFAs) in organic solar cells has led to power conversion efficiencies as high as 18%(1). However, organic solar cells are still less efficient than inorganic solar cells, which typically have power conversion efficiencies of more than 20%(2). A key reason for this difference is that organic solar cells have low open-circuit voltages relative to their optical bandgaps(3), owing to non-radiative recombination(4). For organic solar cells to compete with inorganic solar cells in terms of efficiency, non-radiative loss pathways must be identified and suppressed. Here we show that in most organic solar cells that use NFAs, the majority of charge recombination under open-circuit conditions proceeds via the formation of non-emissive NFA triplet excitons; in the benchmark PM6:Y6 blend(5), this fraction reaches 90%, reducing the open-circuit voltage by 60 mV. We prevent recombination via this non-radiative channel by engineering substantial hybridization between the NFA triplet excitons and the spin-triplet charge-transfer excitons. Modelling suggests that the rate of back charge transfer from spin-triplet charge-transfer excitons to molecular triplet excitons may be reduced by an order of magnitude, enabling re-dissociation of the spin-triplet charge-transfer exciton. We demonstrate NFA systems in which the formation of triplet excitons is suppressed. This work thus provides a design pathway for organic solar cells with power conversion efficiencies of 20% or more. A substantial pathway for energy loss in organic solar cells may be suppressed by engineering hybridization between non-fullerene acceptor triplet excitons and spin-triplet charge transfer excitons.
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| 3. |
- Hopper, Thomas R., et al.
(författare)
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Control of Donor-Acceptor Photophysics through Structural Modification of a "Twisting" Push-Pull Molecule
- 2019
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Ingår i: Chemistry of Materials. - : AMER CHEMICAL SOC. - 0897-4756 .- 1520-5002. ; 31:17, s. 6860-6869
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Tidskriftsartikel (refereegranskat)abstract
- In contemporary organic solar cell (OSC) research, small A-D-A molecules comprising electron donor (D) and acceptor (A) units are increasingly used as a means to control the optoelectronic properties of photovoltaic blends. Slight structural variations to these A-D-A molecules can result in profound changes to the performance of the OSCs. Herein, we study two A-D-A molecules, BTCN-O and BTCN-M, which are identical in structure apart from a subtle difference in the position of alkyl chains, which force the molecules to adopt different equilibrium conformations. These steric effects cause the respective molecules to work better as an electron donor and acceptor when blended with benchmark acceptor and donor materials (PC71BM and PBDB-T). We study the photophysics of these "D:A" blends and devices using a combination of steady-state and time-resolved spectroscopic techniques. Time-resolved photoluminescence reveals the impact of the molecular conformation on the quenching of the A-D-A emission when BTCN-O and BTCN-M are blended with PBDB-T or PC71BM. Ultrafast broadband transient absorption spectroscopy demonstrates that the dynamics of charge separation are essentially identical when comparing BTCN-M and BTCN-O based blends, but the recombination dynamics are quite dissimilar. This suggests that the device performance is ultimately determined by the morphology of the blends imposed by the A-D-A conformation. This notion is supported by X-ray scattering measurements on the "D:A" films, electroluminescence data, and pump-push-photocurrent spectroscopy on the "D:A" devices. Our findings provide insight into the remarkable structure-function relationship in A-D-A molecules and emphasize the need for careful morphological and energetic considerations when designing high-performance OSCs.
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| 4. |
- Jasiunas, Rokas, et al.
(författare)
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From Generation to Extraction: A Time-Resolved Investigation of Photophysical Processes in Non-fullerene Organic Solar Cells
- 2020
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:39, s. 21283-21292
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Tidskriftsartikel (refereegranskat)abstract
- Non-fullerene organic solar cells (NFOSCs) demonstrate record efficiencies exceeding 16%. In comparison with cells with the fullerene-based acceptor, the NFOSCs benefit from a longer wavelength absorption, which leads to a small highest occupied molecular orbital (HOMO) level offset. Here, we use several advanced transient investigation techniques, covering timescale from sub-ps to mu s, to address all sequence of processes starting from photoexcitation of donors or acceptors to carrier extraction in several NFOSCs and cells with phenyl-C71-butyric acid methyl ester (PCBM). Though small offsets result in higher open-circuit voltage, we show that at the same time, it limits cell performance because of inefficient hole transfer from excited acceptors to donors and enhanced geminate recombination. We demonstrate that 100 meV HOMO level offset and proper acceptor molecule structures are sufficient for efficient hole transfer (>70%) and for reduction of the geminate recombination losses down to about 20%. Subsequent extraction of unbound charge carriers in all NFOSCs is slightly faster than in cells with PCBM, while non-geminate carrier recombination causing additional losses is slightly slower in the best performing NFOSCs than in cells with PCBM.
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| 5. |
- Li, Yongxi, et al.
(författare)
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A fused-ring based electron acceptor for efficient non-fullerene polymer solar cells with small HOMO offset
- 2016
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Ingår i: NANO ENERGY. - : ELSEVIER SCIENCE BV. - 2211-2855. ; 27, s. 430-438
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Tidskriftsartikel (refereegranskat)abstract
- A non-fullerene electron acceptor bearing a novel backbone with fused 10-heterocyclic ring (in-dacenodithiopheno-indacenodiselenophene), denoted by IDTIDSe-IC is developed for fullerene free polymer solar cells. IDTIDSe-IC exhibits a low band gap (E-g=1.52 eV) and strong absorption in the 600850 nm region. Combining with a large band gap polymer J51 (E-g=1.91 eV) as donor, broad absorption coverage from 300 nm to 800 nm is obtained due to complementary absorption of J51 and IDTIDSe-IC, which enables a high PCE of 8.02% with a V-oc of 0.91 V, a J(SC) of 15.16 mA/cm(2) and a FF of 58.0% in the corresponding PSCs. Moreover, the EQE of 50-65% is achieved in the absorption range of IDTIDSe-IC with only about 0.1 eV HOMO difference between J51 and IDTIDSe-IC. (C) 2016 Elsevier Ltd. All rights reserved.
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| 6. |
- Liu, Jing, et al.
(författare)
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Fast charge separation in a non-fullerene organic solar cell with a small driving force
- 2016
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Ingår i: NATURE ENERGY. - : NATURE PUBLISHING GROUP. - 2058-7546. ; 1
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Tidskriftsartikel (refereegranskat)abstract
- Fast and efficient charge separation is essential to achieve high power conversion efficiency in organic solar cells (OSCs). In state-of-the-art OSCs, this is usually achieved by a significant driving force, defined as the offset between the bandgap (E-gap) of the donor/acceptor materials and the energy of the charge transfer (CT) state (E-CT), which is typically greater than 0.3 eV. The large driving force causes a relatively large voltage loss that hinders performance. Here, we report non-fullerene OSCs that exhibit ultrafast and efficient charge separation despite a negligible driving force, as E-CT is nearly identical to E-gap. Moreover, the small driving force is found to have minimal detrimental effects on charge transfer dynamics of the OSCs. We demonstrate a non-fullerene OSC with 9.5% efficiency and nearly 90% internal quantum efficiency despite a low voltage loss of 0.61V. This creates a path towards highly efficient OSCs with a low voltage loss.
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| 7. |
- Planes, Emilie, et al.
(författare)
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Encapsulation Effect on Performance and Stability of Organic Solar Cells
- 2020
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Ingår i: Advanced Materials Interfaces. - : WILEY. - 2196-7350. ; 7:15
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Tidskriftsartikel (refereegranskat)abstract
- To increase the lifetime of organic photovoltaic (OPV) devices and pass European lifetime standards, some encapsulation systems are often used to limit the exposition to oxygen and humidity of solar cells. Despite this progress, the damages induced by the encapsulation process are scarcely studied in literature. In this article, the consequences of the common roll-to-roll and vacuum lamination approaches are investigated and compared. The losses of performances are first followed induced by both the encapsulation itself and in a damp heat ageing. The vacuum lamination seems harmless for the solar cells. However, a significant damage is evidenced, even with a relatively mild roll-to-roll encapsulation. The degradation mechanisms are further investigated by complementary imaging characterization tools: photoluminescence/electroluminescence imaging and spectroscopy, laser-beam-induced current mapping, and correlated toJ(V) curves. The recent advancements in the optoelectronic domain may allow linking cell performance to localized flaws. It appears that, although the processing conditions are rather homogeneous, the resulting degradation ends up with a strong localization feature.
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| 8. |
- Qian, Deping, et al.
(författare)
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Correlating the Hybridization of Local-Exciton and Charge-Transfer States with Charge Generation in Organic Solar Cells
- 2023
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Ingår i: Advanced Energy Materials. - : WILEY-V C H VERLAG GMBH. - 1614-6832 .- 1614-6840. ; 13
-
Tidskriftsartikel (refereegranskat)abstract
- In organic solar cells with very small energetic-offset (& UDelta;ELE - CT), the charge-transfer (CT) and local-exciton (LE) states strongly interact via electronic hybridization and thermal population effects, suppressing the non-radiative recombination. Here, we investigated the impact of these effects on charge generation and recombination. In the blends of PTO2:C8IC and PTO2:Y6 with very small, ultra-fast CT state formation was observed, and assigned to direct photoexcitation resulting from strong hybridization of the LE and CT states (i.e., LE-CT intermixed states). These states in turn accelerate the recombination of both CT and charge separated (CS) states. Moreover, they can be significantly weakened by an external-electric field, which enhanced the yield of CT and CS states but attenuated the emission of the device. This study highlights that excessive LE-CT hybridization due to very low , whilst enabling direct and ultrafast charge transfer and increasing the proportion of radiative versus non-radiative recombination rates, comes at the expense of accelerating recombination losses competing with exciton-to-charge conversion process, resulting in a loss of photocurrent generation.
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| 9. |
- Qian, Deping, et al.
(författare)
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Design rules for minimizing voltage losses in high-efficiency organic solar cells
- 2018
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Ingår i: Nature Materials. - : NATURE PUBLISHING GROUP. - 1476-1122 .- 1476-4660. ; 17:8, s. 703-
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Tidskriftsartikel (refereegranskat)abstract
- The open-circuit voltage of organic solar cells is usually lower than the values achieved in inorganic or perovskite photovoltaic devices with comparable bandgaps. Energy losses during charge separation at the donor-acceptor interface and non-radiative recombination are among the main causes of such voltage losses. Here we combine spectroscopic and quantum-chemistry approaches to identify key rules for minimizing voltage losses: (1) a low energy offset between donor and acceptor molecular states and (2) high photoluminescence yield of the low-gap material in the blend. Following these rules, we present a range of existing and new donor-acceptor systems that combine efficient photocurrent generation with electroluminescence yield up to 0.03%, leading to non-radiative voltage losses as small as 0.21 V. This study provides a rationale to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.
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| 10. |
- Qian, Deping
(författare)
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Studies of Voltage Losses in Organic Solar Cells
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Organic photovoltaic (OPV) devices based on semiconducting polymers and small molecules are potential alternatives to inorganic solar cells, owing to their advantages of being inexpensive, lightweight, flexible and suitable for roll-to-roll production. The state of art organic solar cells (OSCs) performed power conversion efficiencies (PCEs) over 13%.The quantum efficiency losses in OSCs have been significantly reduced within the charge generation and extraction processes, resulting in high EQEPV (70-90%) and high FF (70-80%). Whereas, large voltage losses (Δ? = ??/? − ???) were observed in conventional fullerene based solar cells, and it has been the main limiting factor for further OPV advancement. Therefore, strategies to reduce the voltage losses are required.In this thesis, newly designed non-fullerene (NF) acceptors are used to construct novel material systems for high efficiency solar cells. In particular, we studied the hole transfer in these fullerene free systems. We also reported a NF system that exhibit ultrafast and efficient charge separation despite a negligible driving force, as ECT is nearly identical to ??. Moreover, the small driving force is found to have minimal detrimental effects on charge transfer dynamics of the OSCs. We demonstrate a NF based OSC with efficiency of 9.5% and internal quantum efficiency nearly 90% despite a low voltage loss of 0.61 V. This creates a path towards highly efficient OSCs with a low voltage loss.CT states in OSCs are also investigated, since VOC is governed by the CT energy (ECT), which is found as ???? = ??? − 0.6 in a large set of fullerene based solar cells. In order to reduce these recombination losses from CT states, we explored polymer-diPDI systems which exhibited weakened D-A coupling strength, due to the steric hindrance effect. The radiative recombination losses at D/A interface in these NF devices are all reduced to less than 0.18 eV. In particular, in some cases, the additional emission from pure material is favorable for suppressing the non-radiative CT states decay. Consequently, the recombination losses in these NF systems are reduced to 0.5 eV, while the charge generation is still efficient as confirmed by PL quenching and EQEPV.Novel material systems based on non-fullerene acceptors are investigated. The systems performed energy offsets (ΔHOMO or ΔLUMO) less than 0.15eV, resulting in the same energy of CT states and bulk excitons. In this regard, the charge transfer energy loss is minimized. We also found that the EL spectra as well as the EQEEL of the blend solar cells are similar with that of lower gap components in blends. Thus the non-radiative voltage losses are reduced to < 0.3V and small voltage loss of 0.5-0.7V are obtained. Meanwhile, the charge generation in systems are still efficient and high EQEPV of 50-70% can be achieved. It confirms that there is no intrinsic limit for the VOC and efficiency of OPVs as compared with other photovoltaic technologies.
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| 11. |
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| 12. |
- Wang, Yuming, et al.
(författare)
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Light-induced degradation of fullerenes in organic solar cells : a case study on TQ1:PC71BM
- 2018
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 6:25, s. 11884-11889
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Tidskriftsartikel (refereegranskat)abstract
- The stability of organic solar cells (OSCs) is critical for practical applications of this emerging technology. Unfortunately, in spite of intensive investigations, the degradation mechanisms in OSCs have not been clearly understood yet. In this report, we employ a range of spectroscopic and transport measurements, coupled with drift-diffusion modelling, to investigate the light-induced degradation mechanisms of fullerene-based OSCs. We find that trap states formed in the fullerene phase under illumination play a critical role in the degradation of the open-circuit voltage (V-OC) in OSCs. Our results indicate that the degradation is intrinsic to the fullerenes in OSCs and that alternative acceptor materials are desired for the development of stable OSCs.
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| 13. |
- Wang, Yuming, et al.
(författare)
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Optical Gaps of Organic Solar Cells as a Reference for Comparing Voltage Losses
- 2018
-
Ingår i: Advanced Energy Materials. - : WILEY-V C H VERLAG GMBH. - 1614-6832 .- 1614-6840. ; 8:28
-
Tidskriftsartikel (refereegranskat)abstract
- The voltage loss, determined by the difference between the optical gap (E-g) and the open-circuit voltage (V-OC), is one of the most important parameters determining the performance of organic solar cells (OSCs). However, the variety of different methods used to determine E-g makes it hard to fairly compare voltages losses among different material systems. In this paper, the authors discuss and compare various E-g determination methods and show how they affect the detailed calculation of voltage losses, as well as predictions of the maximum achievable power conversion efficiency. The aim of this paper is to make it possible for the OSC community to compare voltage losses in a consistent and reasonable way. It is found that the voltage losses for strongly absorbed photons in state-of-the-art OSCs are not much less than 0.6 V, which still must be decreased to further enhance efficiency.
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| 14. |
- Wang, Yuming, et al.
(författare)
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Origins of the open-circuit voltage in ternary organic solar cells and design rules for minimized voltage losses
- 2023
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Ingår i: Nature Energy. - : NATURE PORTFOLIO. - 2058-7546. ; 8:9, s. 978-988
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Tidskriftsartikel (refereegranskat)abstract
- The power conversion efficiency of ternary organic solar cells (TOSCs), consisting of one host binary blend and one guest component, remains limited by large voltage losses. The fundamental understanding of the open-circuit voltage (V-OC) in TOSCs is controversial, limiting rational design of the guest component. In this study, we systematically investigate how the guest component affects the radiative and non-radiative related parts of V-OC of a series of TOSCs using the detailed balanced principle. We highlight that the thermal population of charge-transfer and local exciton states provided by the guest binary blend (that is, the guest-component-based binary blend) has a significant influence on the non-radiative voltage losses. Ultimately, we provide two design rules for enhancing the V-OC in TOSCs: high emission yield for the guest binary blend and similar charge-transfer-state energies for host/guest binary blends; high miscibility of the guest component with the low gap component in the host binary blend. The performance of ternary organic solar cells is limited by voltage losses. Using the detailed balance principle, Wang et al. show how the third component of the blend affects the open-circuit voltage and delineate molecular design rules.
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| 15. |
- Whelan, Patrick R., et al.
(författare)
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Fermi velocity renormalization in graphene probed by terahertz time-domain spectroscopy
- 2020
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Ingår i: 2D Materials. - : IOP Publishing. - 2053-1583. ; 7:3
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate terahertz time-domain spectroscopy (THz-TDS) to be an accurate, rapid and scalable method to probe the interaction-induced Fermi velocity renormalization nu F*10(12) cm(-2), Fermi level > 0.1 eV). From an application point of view, the ability to rapidly and non-destructively quantify and map the electrical (sigma(DC), n, mu) and electronic ( nu F*
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| 16. |
- Xu, Bo, et al.
(författare)
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Integrated Design of Organic Hole Transport Materials for Efficient Solid-State Dye-Sensitized Solar Cells
- 2015
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Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6832 .- 1614-6840. ; 5:3
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Tidskriftsartikel (refereegranskat)abstract
- A series of triphenylamine-based small molecule organic hole transport materials (HTMs) with low crystallinity and high hole mobility are systematically investigated in solid-state dye-sensitized solar cells (ssDSCs). By using the organic dye LEG4 as a photosensitizer, devices with X3 and X35 as the HTMs exhibit desirable power conversion efficiencies (PCEs) of 5.8% and 5.5%, respectively. These values are slightly higher than the PCE of 5.4% obtained by using the state-of-the-art HTM Spiro-OMeTAD. Meanwhile, transient photovoltage decay measurement is used to gain insight into the complex influences of the HTMs on the performance of devices. The results demonstrate that smaller HTMs induce faster electron recombination in the devices and suggest that the size of a HTM plays a crucial role in device performance, which is reported for the first time.
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| 17. |
- Yang, Fan, et al.
(författare)
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Performance limitations in thieno[3,4-c] pyrrole4,6-dione-based polymer: ITIC solar cells
- 2017
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 19:35, s. 23990-23998
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Tidskriftsartikel (refereegranskat)abstract
- We report a systematic study of the efficiency limitations of non-fullerene organic solar cells that exhibit a small energy loss (E-loss) between the polymer donor and the non-fullerene acceptor. To clarify the impact of Eloss on the performance of the solar cells, three thieno[3,4-c] pyrrole-4,6-dione-based conjugated polymers (PTPD3T, PTPD2T, and PTPDBDT) are employed as the electron donor, which all have complementary absorption spectra compared with the ITIC acceptor. The corresponding photovoltaic devices show that low Eloss (0.54 eV) in PTPDBDT: ITIC leads to a high open-circuit voltage (Voc) of 1.05 V, but also to a small quantum efficiency, and in turn photocurrent. The high Voc or small energy loss in the PTPDBDT-based solar cells is a consequence of less non-radiative recombination, whereas the low quantum efficiency is attributed to the unfavorable micro-phase separation, as confirmed by the steady-state and time-resolved photoluminescence experiments, grazing-incidence wide-angle X-ray scattering, and resonant soft X-ray scattering (R-SoXS) measurements. We conclude that to achieve high performance non-fullerene solar cells, it is essential to realize a large Voc with small Eloss while simultaneously maintaining a high quantum efficiency by manipulating the molecular interaction in the bulk-heterojunction.
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| 18. |
- Yao, Huifeng, et al.
(författare)
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14.7% Efficiency Organic Photovoltaic Cells Enabled by Active Materials with a Large Electrostatic Potential Difference
- 2019
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 141:19, s. 7743-7750
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Tidskriftsartikel (refereegranskat)abstract
- Although significant improvements have been achieved for organic photovoltaic cells (OPVs), the top-performing devices still show power conversion efficiencies far behind those of commercialized solar cells. One of the main reasons is the large driving force required for separating electron-hole pairs. Here, we demonstrate an efficiency of 14.7% in the single-junction OPV by using a new polymer donor PTO2 and a nonfullerene acceptor IT-4F. The device possesses an efficient charge generation at a low driving force. Ultrafast transient absorption measurements probe the formation of loosely bound charge pairs with extended lifetime that impedes the recombination of charge carriers in the blend. The theoretical studies reveal that the molecular electrostatic potential (ESP) between PTO2 and IT-4F is large, and the induced intermolecular electric field may assist the charge generation. The results suggest OPVs have the potential for further improvement by judicious modulation of ESP.
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| 19. |
- Yao, Huifeng, et al.
(författare)
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Critical Role of Molecular Electrostatic Potential on Charge Generation in Organic Solar Cells
- 2018
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Ingår i: Chinese journal of chemistry. - : WILEY-V C H VERLAG GMBH. - 1001-604X .- 1614-7065. ; 36:6, s. 491-494
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Tidskriftsartikel (refereegranskat)abstract
- Revealing the charge generation is a crucial step to understand the organic photovoltaics. Recent development in non-fullerene organic solar cells (OSCs) indicates efficient charge separation even with negligible energetic offset between the donor and acceptor materials. These new findings trigger a critical question concerning the charge separation mechanism in OSCs, traditionally believed to result from sufficient energetic offset between the polymer donor and fullerene acceptor. We propose a new mechanism, which involves the molecular electrostatic potential, to explain efficient charge separation in non-fullerene OSCs. Together with the new mechanism, we demonstrate a record efficiency of similar to 12% for systems with negligible energetic offset between donor and acceptor materials. Our analysis also rationalizes different requirement of the energetic offset between fullerene-based and non-fullerene OSCs, and paves the way for further design of OSC materials with both high photocurrent and high photovoltage at the same time.
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| 20. |
- 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. ; 11
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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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| 21. |
- Zhao, Wenchao, et al.
(författare)
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Fullerene-Free Polymer Solar Cells with over 11% Efficiency and Excellent Thermal Stability
- 2016
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Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 28:23, s. 4734-4739
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Tidskriftsartikel (refereegranskat)abstract
- A nonfullerene-based polymer solar cell (PSC) that significantly outperforms fullerene-based PSCs with respect to the power-conversion efficiency is demonstrated for the first time. An efficiency of amp;gt;11%, which is among the top values in the PSC field, and excellent thermal stability is obtained using PBDB-T and ITIC as donor and acceptor, respectively.
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| 22. |
- Zhou, Zichun, et al.
(författare)
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Subtle Molecular Tailoring Induces Significant Morphology Optimization Enabling over 16% Efficiency Organic Solar Cells with Efficient Charge Generation
- 2020
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Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 32:4
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Tidskriftsartikel (refereegranskat)abstract
- Manipulating charge generation in a broad spectral region has proved to be crucial for nonfullerene-electron-acceptor-based organic solar cells (OSCs). 16.64% high efficiency binary OSCs are achieved through the use of a novel electron acceptor AQx-2 with quinoxaline-containing fused core and PBDB-TF as donor. The significant increase in photovoltaic performance of AQx-2 based devices is obtained merely by a subtle tailoring in molecular structure of its analogue AQx-1. Combining the detailed morphology and transient absorption spectroscopy analyses, a good structure-morphology-property relationship is established. The stronger pi-pi interaction results in efficient electron hopping and balanced electron and hole mobilities attributed to good charge transport. Moreover, the reduced phase separation morphology of AQx-2-based bulk heterojunction blend boosts hole transfer and suppresses geminate recombination. Such success in molecule design and precise morphology optimization may lead to next-generation high-performance OSCs.
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