Morphological Control Agent in Ternary Blend Bulk Heterojunction Solar Cells

Liao, Hsueh Chung; Chen, Po Hsuen; Chang, Robert P. H.; Su, Wei

doi:10.3390/polym6112784

Cited by 28 publications

(14 citation statements)

References 72 publications

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“…The third component can play a role of a template to facilitate supramolecular assembly in the blend film to form ideal BHJ morphology, favoring exciton dissociation and charge transport . Recently, several ternary systems have utilized the ternary strategy to optimize the morphology and improve the efficiency of OSCs …”

Section: Methods To Control Morphologymentioning

confidence: 99%

Morphology Control in Organic Solar Cells

Zhao

Wang

Zhan

2018

Advanced Energy Materials

501

394

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the working mechanism includes four key steps (as shown in Figure 1): (1) light absorption and Frenkel exciton generation; (2) exciton diffusion to the D/A interface; (3) exciton dissociation into free charge carrier; (4) charge transport and collection. Each step is very important and could become a bottleneck leading to an inferior performance of OSCs. The second and forth steps are dominated by the morphology of the active layer. Since the Frenkel excitons are tightly bounded by Coulombic force, the lifetime of exciton is limited and its diffusion length is only 5-14 nm. [8][9][10] As a result, the domain size should be confined in 5-30 nm to ensure excitons reach D/A interfacial zone and then dissociate into free charge carriers efficiently. On the other hand, high domain purity and fine bicontinuous interpenetrating network nanostructure are also necessary to enable the charge carriers transfer to the electrodes quickly and reduce the bimolecular recombination.The PCE is the overall parameter to evaluate the performance of OSCs, which is the product of open-circuit voltage (V OC ), short-circuit current density (J SC ), and fill factor (FF). Since V OC is proportional to the difference of the highest occupied molecular orbital energy level of the donor and the lowest unoccupied molecular orbital energy level of the acceptor, [11][12][13] the V OC is mainly determined by the donor and acceptor materials. However, V OC is also related to the morphology of the active layer, such as D/A interface area, microstructure, crystallinity and so on. [14] The J SC is dominated by the whole photoelectric conversion process, namely exciton generation, diffusion and dissociation, and charge transport and collection. Among them, efficient exciton diffusion and dissociation, and charge transport strongly depend on the fine morphology of the active layer. [15] FF represents the diode characteristic of the device and is bound up with the charge transport and recombination in the active layer. The fast charge transport and low charge recombination also mainly depend on the morphology, such as crystallinity, molecular orientation, domain purity, vertical phase separation, etc. [15] Therefore, the ideal morphology of the active layer is the crucial factor to achieve high-performance OSCs.The nanomorphology of the active layer is affected by various factors, such as the D/A properties (solubility, crystallinity, miscibility, etc.), film processing, device configuration, and so on. There are only several successful as-cast films affording satisfactory morphology and performance [16][17][18] since it is very hard to obtain ideal morphology and good performance just depending energy and present some advantages, such as low cost, light weight, flexibility, semitransparency, and roll-to-roll large-area fabrication. Due to the short diffusion length of exciton (≈10 nm) in organic semiconductor materials, the ideal nanoscale phase separation in the active layer is one of the crucial factors for achieving efficient exciton dissociation an...

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Section: Methods To Control Morphologymentioning

confidence: 99%

Morphology Control in Organic Solar Cells

Zhao

Wang

Zhan

2018

Advanced Energy Materials

501

394

View full text Add to dashboard Cite

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“…Common motivations for adding additional BHJ components are improving light harvesting by extending film absorption, reducing charge recombination through energetic offsets, but also includes morphological control . Indeed, the optimal BHJ morphology for a given ternary blend depends on the intended function of the additional component, e.g., whether it forms an alloyed phase, part of an interfacial energetic cascade, or a parallel transport pathway . The ternary component can also serve as a morphological control agent, reducing the need for solvent additives or synergistically enhancing their effects.…”

Section: Future Of Solvent Additive Processing In Organic Photovoltaicsmentioning

confidence: 99%

Solvent Additives: Key Morphology‐Directing Agents for Solution‐Processed Organic Solar Cells

et al. 2018

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Organic photovoltaics (OPV) have the advantage of possible fabrication by energy-efficient and cost-effective deposition methods, such as solution processing. Solvent additives can provide fine control of the active layer morphology of OPVs by influencing film formation during solution processing. As such, solvent additives form a versatile method of experimental control for improving organic solar cell device performance. This review provides a brief history of solution-processed bulk heterojunction OPVs and the advent of solvent additives, putting them into context with other methods available for morphology control. It presents the current understanding of how solvent additives impact various mechanisms of phase separation, enabled by recent advances in in situ morphology characterization. Indeed, understanding solvent additives' effects on film formation has allowed them to be applied and combined effectively and synergistically to boost OPV performance. Their success as a morphology control strategy has also prompted the use of solvent additives in related organic semiconductor technologies. Finally, the role of solvent additives in the development of next-generation OPV active layers is discussed. Despite concerns over their environmental toxicity and role in device instability, solvent additives remain relevant morphological directing agents as research interests evolve toward nonfullerene acceptors, ternary blends, and environmentally sustainable solvents.

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“…Therefore, morphology controlling has become one of research key points and still faces a great challenge. Some practical physical strategies have been developed such as ternary blend, additives, thermal annealing, etc., to finely tune blend morphology and form miscible donor/acceptor mixture . In the meantime, exploitation of chemical tools as an alternative strategy to control blend morphology is showing its advantages in finely molecular‐scaled controlling .…”

Section: Introductionmentioning

confidence: 99%

Steric Engineering of Alkylthiolation Side Chains to Finely Tune Miscibility in Nonfullerene Polymer Solar Cells

Xue

Weng

Feng

et al. 2018

Advanced Energy Materials

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advantages of simple device structure, light weight, and low fabrication cost by solution-processing. [1][2][3][4][5][6][7][8][9][10][11] Despite the great achievement in fullerene PSCs, fullerene acceptors still suffer from several drawbacks, including high-cost purification, poor morphological stability, and weak absorption in visible wavelength range. To solve these problems, considerable research efforts have been dedicated to nonfullerene acceptors, especially smallmolecular acceptors (SMAs). [12][13][14][15][16][17][18][19][20] Recently, emerging SMAs have been demonstrated as alternatives to fullerene acceptors because the excellent photovoltaic performance with power conversion efficiency (PCE) has reached 12-14% recently. [18][19][20][21] To achieve more efficient SMA PSCs, it is essential to design donor polymers that can match with SMAs through favorable morphology as the device performance of PSCs is strongly dependent on the blend morphology. Therefore, morphology controlling has become one of research key points and still faces a great challenge. Some practical physical strategies have been developed such as ternary blend, additives, thermal annealing, etc., to finely tune blend morphology and form miscible donor/acceptor mixture. [22,23] In the meantime, exploitation of chemical tools as an alternative strategy to control blend morphology is showing its advantages in finely molecular-scaled controlling. [24] One of the most commonly used chemical strategies for tuning morphology is through the fluorination or alkylthiolation of the polymeric side chains to tune the solubility, aggregation properties, and thus the good miscibility with acceptors. [25] In comparison with the high cost and complex synthetic route of fluorinated modification on polymer side chains, low cost of alkylthiolation is obviously synthetic superior to the former. However, in recent literatures it is found that, on the one hand, the alkylthiolation of polymer side chains can improve polymeric crystallinity and mobility and lead to a high photovoltaic performance; [26,27] on the other hand, the strengthened crystallinity after the alkylthiolation for high crystalline polymer may form dense and isolated polymer domains, which causes serious phase separation and destroys the miscibility at donor/acceptor interfaces. [24,28,29] As the thermodynamic miscibility between donor and acceptor mainly drives the phase separation degree, therefore, Morphology and miscibility control are still a great challenge in polymer solar cells. Despite physical tools being applied, chemical strategies are still limited and complex. To finely tune blend miscibility to obtain optimized morphology, chemical steric engineering is proposed to systemically investigate its effects on optical and electronic properties, especially on a balance between crystallinity and miscibility. By changing the alkylthiol side chain orientation different steric effects are realized in three different polymers. Surprisingly, the photovoltaic device of the polymer PTBB-m with...

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Morphological Control Agent in Ternary Blend Bulk Heterojunction Solar Cells

Cited by 28 publications

References 72 publications

Morphology Control in Organic Solar Cells

Morphology Control in Organic Solar Cells

Solvent Additives: Key Morphology‐Directing Agents for Solution‐Processed Organic Solar Cells

Steric Engineering of Alkylthiolation Side Chains to Finely Tune Miscibility in Nonfullerene Polymer Solar Cells

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