Synergistic Effects of Morphological Control and Complementary Absorption in Efficient All-Small-Molecule Ternary-Blend Solar Cells

Farahat, Mahmoud E.; Patra, Dhananjaya; Lee, Chih‐Hao; Chu, Chih‐Wei

doi:10.1021/acsami.5b06831

Cited by 22 publications

(11 citation statements)

References 51 publications

(99 reference statements)

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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

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“…[3a,4b,5] With the use of processing additives or solvent vapor annealing (SVA) techniques,[1c,f,7] several recent works have reported all‐SM devices with attainable higher PCEs, rivaling those of polymer–fullerene BHJ solar cells (and beyond). [3a,7a,c] All‐SM solar cells must concurrently involve a suitable combination of SM donor and acceptor materials, addressing spectral complementarity and energy band‐edge alignments …”

Section: Introductionmentioning

confidence: 99%

Higher Mobility and Carrier Lifetimes in Solution‐Processable Small‐Molecule Ternary Solar Cells with 11% Efficiency

Liang

Zhang

Savikhin

et al. 2018

Advanced Energy Materials

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shown to reach power conversion efficiencies (PCEs) >10%, [2] the synthesis of π-conjugated polymers with specific optical gaps and little-to-no batch-to-batch variation remains a practical limitation in the scaling-up of high-efficiency polymerfullerene BHJ devices. [3] In parallel, the narrow spectral absorption of fullerene acceptors (e.g., [6,6]-phenyl-C 61 (or C 71 )butyric acid methyl ester, namely, PC 61 BM and PC 71 BM) falling in the short-wavelengths region (≈300-450 nm) inherently limits photonic absorption, since most of the photon flux occurs in the visible range of the solar spectrum (>450 nm). By contrast, all-SM BHJ solar cells can involve two visible light absorbers-, i.e., π-extended SM donor and SM acceptorthus, all-SM devices could in principle produce higher photocurrents and outperform their polymer-fullerene BHJ counterparts. [1g,4] SM materials feature on the properties of being well-defined, size-monodispersed, and scalable. "Nonfullerene" SM acceptors add the benefit of being synthetically accessible in controlled purities, while these may also be readily produced on large scales. Nevertheless, reaching high PCE values with the all-SM device approach has remained challenging thus far, mainly owing to i) morphology limitations prevailing in the absence of polymer (e.g., lack of control over domain sizes, crystallinity, among other important aspects) and ii) the difficulty to reach the enhancement and balance of charge transport in active layers. [3a,4b,5] With the use of processing additives [6] or solvent vapor annealing (SVA) Solution-processed small molecule (SM) solar cells have the prospect to outperform their polymer-fullerene counterparts. Considering that both SM donors/acceptors absorb in visible spectral range, higher expected photocurrents should in principle translate into higher power conversion efficiencies (PCEs). However, limited bulk-heterojunction (BHJ) charge carrier mobility (<10-4 cm 2 V -1 s -1 ) and carrier lifetimes (<1 µs) often impose active layer thickness constraints on BHJ devices (≈100 nm), limiting external quantum efficiencies (EQEs) and photocurrent, and making largescale processing techniques particularly challenging. In this report, it is shown that ternary BHJs composed of the SM donor DR3TBDTT (DR3), the SM acceptor ICC6 and the fullerene acceptor PC 71 BM can be used to achieve SM-based ternary BHJ solar cells with active layer thicknesses >200 nm and PCEs nearing 11%. The examinations show that these remarkable figures are the result of i) significantly improved electron mobility (8.2 × 10 -4 cm 2 V -1 s -1 ), ii) longer carrier lifetimes (2.4 µs), and iii) reduced geminate recombination within BHJ active layers to which PC 71 BM has been added as ternary component. Optically thick (up to ≈500 nm) devices are

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“…The TOSCs based on 2D and 1A ternary components have been successfully designed and significant enhancement in PCE has been achieved. [ 68–72 ] Specially, in the FRET‐based ternary system, [ 73 ] the third component in the FRET could be the “energy donor” or the “energy acceptor.”…”

Section: Materials Used In Tosc Based On Fretmentioning

confidence: 99%

Recent Advances in Ternary Organic Solar Cells Based on Förster Resonance Energy Transfer

Wang

Yang

et al. 2021

Solar RRL

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Recently, Förster resonance energy transfer (FRET)‐based strategy has been successfully applied to promote the efficiencies of ternary blend organic solar cells (TOSCs). However, the intrinsic mechanism of FRET in the observed enhancement of efficiency has not been deconvolved unambiguously due to the complex photophysics mechanism. In this review, by deeply analyzing recent examples of FRET‐incorporated TOSCs, diverse framework structures of FRET pairs are summarized, then the theory, prerequisites, and the confirmation methods for FRET are discussed. In particular, the role of FRET theory in the photoconversion process is discussed in detail, including exciton harvesting, exciton diffusion, and charge generation. Finally, the existing challenges and future research directions of FRET applications in TOSCs are proposed.

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Synergistic Effects of Morphological Control and Complementary Absorption in Efficient All-Small-Molecule Ternary-Blend Solar Cells

Cited by 22 publications

References 51 publications

Morphology Control in Organic Solar Cells

Morphology Control in Organic Solar Cells

Higher Mobility and Carrier Lifetimes in Solution‐Processable Small‐Molecule Ternary Solar Cells with 11% Efficiency

Recent Advances in Ternary Organic Solar Cells Based on Förster Resonance Energy Transfer

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