Small‐Molecule Solar Cells with Simultaneously Enhanced Short‐Circuit Current and Fill Factor to Achieve 11% Efficiency

Li, Nian; Gao, Ke; Jiang, Yufeng; Qiu, Rong; Hu, Xiaowen; Yuan, Dong; Liu, Feng; Peng, Xiaobin; Russell, Thomas P.; Zhou, Guofu

doi:10.1002/adma.201700616

Cited by 90 publications

(72 citation statements)

References 32 publications

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“…Mobility in chiral materials is known to be extremely sensitive to supramolecular organisation . Morphological analysis revealed that the asymmetric compound is the more inclined to form ordered crystalline domains when spun‐cast as a blend with PC 61 BM, which could be of interest for larger molecules based on similar materials with greater charge transport …”

Section: Discussionmentioning

confidence: 99%

Self‐Assembly of Chiral‐at‐End Diketopyrrolopyrroles: Symmetry Dependent Solution and Film Optical Activity and Photovoltaic Performance

Hume

Monks

Pop

et al. 2018

Chemistry A European J

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Chiral thiophene-diketopyrrolopyrrole derivatives have been synthesised to investigate the potential of stereochemistry and symmetry as a means of modulating properties by influencing self-assembly of these purely organic materials. In particular, derivatives of diketopyrrolopyrrole were employed because of their proven interest as dyes, especially for organic solar cells. The natural product myrtenal was used as the source of stereochemistry, introduced through a Kröhnke reaction of a thiophene-bearing pyridinium salt and diketopyrrolopyrroles were prepared through Suzuki coupling with this chiral moiety at one end only as well as at both ends. Absorption spectroscopy and electrochemistry confirmed the potential suitability of the compounds for photovoltaic devices. The nanostructures formed by the compounds have been probed with circular dichroism spectroscopy in solution and in films. It is shown that a chiral C symmetric molecule assembles in solution giving a strong circular dichroic signal while as a film this optical activity is nulled, whereas an asymmetric homologue is most optically active as a thin film. The X-ray crystal structure of the asymmetric compound shows a polar order of the molecules that might explain this observation. The lack of optical activity in solution is very likely a result of the high solubility of the compound. The results reaffirm the sensitivity of circular dichroism spectroscopy to inter-chromophore organisation, whereas absorption spectroscopy in the visible region reveals only slight changes to the bands. The differing order in the compounds also affects their performance in bulk heterojunction photovoltaic devices. Atomic force microscopy of the blended thin films with the fullerene derivative usually employed (PC BM) showed that smooth and well mixed films were achieved, with the conditions required during spin coating depending greatly on the derivative, because of their differing solubility. The apparently better performance of the symmetrical compound (although with very low efficiency) is probably a result of the alignment of the molecules inferred by the circular dichroism experiments, whereas the asymmetric compound presumably adopts a twisted supramolecular organisation.

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Section: Discussionmentioning

confidence: 99%

Self‐Assembly of Chiral‐at‐End Diketopyrrolopyrroles: Symmetry Dependent Solution and Film Optical Activity and Photovoltaic Performance

Hume

Monks

Pop

et al. 2018

Chemistry A European J

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“…[67][68][69] Although our current focus is mainly on the small molecules, conclusions made from this study are expected to be also applicable for the polymer OPVs. [67][68][69] Although our current focus is mainly on the small molecules, conclusions made from this study are expected to be also applicable for the polymer OPVs.…”

Section: Descriptors For Machine Learning Modelsmentioning

confidence: 94%

Toward Predicting Efficiency of Organic Solar Cells via Machine Learning and Improved Descriptors

Sahu

Rao

Troisi

et al. 2018

Advanced Energy Materials

207

220

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include the strong electron-electron interactions and strong electron-phonon couplings as well as the complicated donor/ acceptor (D/A) interface morphology, which are fundamentally different from inorganic semiconductors. [23,24] Therefore, the accurate simulating of OPVs requires high-level theoretical methods in quantum chemistry, quantum dynamics and statistical mechanics, and in recent years there have been substantial progress for the theoretical understanding of many microscopic processes such as charge transport, [25] exciton dissociation, [26,27] singlet fission, [28][29][30] etc. These methods are useful for few benchmark systems but cannot be used to explore the chemical space, i.e., screen a large number of candidate materials.The predictive power of a theoretical model by high-throughput virtual screening has been explored in the recent years. [31][32][33][34][35][36][37][38][39][40] For example, in the Harvard Clean Energy Project (CEP), [41] Aspuru-Guzik and co-workers have screened ≈2.3 million compounds by employing the Scharber model [42,43] to find out efficient new donor molecules for OPVs. Here, the computed energies of the highest occupied molecular orbital (HOMO)/the lowest unoccupied molecular orbital (LUMO) of organic molecules are calibrated to experimentally determined values, and then employing an averaging scheme, energies of HOMO/LUMO are estimated to use them as input in the Scharber model. However, the prediction of PCE of an OPV is much more challenging compared to the energies of orbitals. Very recently, the same research team [44] noticed that the Scharber model, widely used in these virtual screening works, is not accurate enough for the prediction of PCE, and calibration of PCE by considering molecular similarity, molecular weight and band gap energy leads to improvement in correlation between experimental (49 OPVs) and calculated PCE (Pearson's coefficient (r) is increased from 0.30 to 0.43). Further, the Scharber model is only optimized for the PC 61 BM acceptor [42] and a more general model is desired to take account of nonfullerene molecules.In an OPV, energy conversion is accomplished by four consecutive steps: i) absorption of photons and exciton formation, ii) exciton diffusion to D/A interface, iii) exciton dissociation, and iv) transport of holes/electrons to the respective electrode. Taking account of all these processes, the efficiency of a device depends on many microscopic properties of the organic material such as optical gap, charge-carrier mobility, ionization To design efficient materials for organic photovoltaics (OPVs), it is essential to identify the largest number of parameters that control their properties and build a model using these parameters (known as descriptors) for the prediction of the power conversion efficiency (PCE). By constructing a dataset for 280 small molecule OPV systems, it is found that for all high-performing devices, frontier molecular orbitals of donor molecules are nearly degenerated and in such cases, orbitals other than just high...

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“…Encouragingly, the large-area (2.03 cm 2 ) flexible ITO-free NF OSC with doctor-blade printing exhibits a remarkable PCE of 7.6%, which is the highest PCE reported to date in large-area flexible ITO-free doctor-bladed NF OSCs. [33] A strong diffraction peak at 0.50 A −1 is seen in outof-plane direction, coming from other ITIC packing structure. [29] In comparison, a low PCE of 5.86% is obtained in the flexible ITO-free spin-coated OSC (consuming four times more solution than the blade-coated one), which illustrates great benefits of doctor-blade printing for low-cost NF OSC manufacturing.…”

Section: Bis[5-(2-ethylhexyl)-2-thienyl]mentioning

confidence: 97%

Printed Nonfullerene Organic Solar Cells with the Highest Efficiency of 9.5%

Lin

Jin

Dong

et al. 2018

Advanced Energy Materials

Self Cite

103

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The current work reports a high power conversion efficiency (PCE) of 9.54% achieved with nonfullerene organic solar cells (OSCs) based on PTB7‐Th donor and 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene) (ITIC) acceptor fabricated by doctor‐blade printing, which has the highest efficiency ever reported in printed nonfullerene OSCs. Furthermore, a high PCE of 7.6% is realized in flexible large‐area (2.03 cm2) indium tin oxide (ITO)‐free doctor‐bladed nonfullerene OSCs, which is higher than that (5.86%) of the spin‐coated counterpart. To understand the mechanism of the performance enhancement with doctor‐blade printing, the morphology, crystallinity, charge recombination, and transport of the active layers are investigated. These results suggest that the good performance of the doctor‐blade OSCs is attributed to a favorable nanoscale phase separation by incorporating 0.6 vol% of 1,8‐diiodooctane that prolongs the dynamic drying time of the doctor‐bladed active layer and contributes to the migration of ITIC molecules in the drying process. High PCE obtained in the flexible large‐area ITO‐free doctor‐bladed nonfullerene OSCs indicates the feasibility of doctor‐blade printing in large‐scale fullerene‐free OSC manufacturing. For the first time, the open‐circuit voltage is increased by 0.1 V when 1 vol% solvent additive is added, due to the vertical segregation of ITIC molecules during solvent evaporation.

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Small‐Molecule Solar Cells with Simultaneously Enhanced Short‐Circuit Current and Fill Factor to Achieve 11% Efficiency

Cited by 90 publications

References 32 publications

Self‐Assembly of Chiral‐at‐End Diketopyrrolopyrroles: Symmetry Dependent Solution and Film Optical Activity and Photovoltaic Performance

Self‐Assembly of Chiral‐at‐End Diketopyrrolopyrroles: Symmetry Dependent Solution and Film Optical Activity and Photovoltaic Performance

Toward Predicting Efficiency of Organic Solar Cells via Machine Learning and Improved Descriptors

Printed Nonfullerene Organic Solar Cells with the Highest Efficiency of 9.5%

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