Influence of thermal and solvent annealing on the morphology and photovoltaic performance of solution processed, D–A–D type small molecule-based bulk heterojunction solar cells

Kumar, Chitra; Ganesh, K.; Suresh, T.; Sharma, Abhishek; Bhanuprakash, K.; Sharma, Ganesh D.

doi:10.1039/c5ra16812k

Cited by 12 publications

(6 citation statements)

References 72 publications

(78 reference statements)

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“…Typically, the choice of SVA solvent is chosen to be the same one from which the BHJ was cast . Yet in some cases the choice is peculiar . In these cases, SVA solvent selection appears to have been guided by the fact that most examples in the literature use one of three different solvents: dichloromethane (DCM), chloroform (CF), or tetrahydrofuran (THF).…”

Section: Introductionmentioning

confidence: 99%

Toward a Universally Compatible Non‐Fullerene Acceptor: Multi‐Gram Synthesis, Solvent Vapor Annealing Optimization, and BDT‐Based Polymer Screening

et al. 2018

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To highlight the benefits of the organic dye PDI-DPP-PDI for use in fullerenefree organic solar cells, herein is demonstrated how this material can meet scalability demands through a multigram scale direct heteroarylation coupling reaction, and performance demands through a post-deposition solvent vapor annealing treatment. A solvent vapor annealing method has been utilized to screen a comprehensive selection of ethereal, aromatic, and chlorinated solvents. Upon transitioning to these eight alternative solvents, significant performance increase over the chloroform standard is noted for all solvents, with tetrahydrofuran and o-dichlorobenzene leading to the highest performance devices post-treatment. This trend, including an open-circuit voltage greater than 1 V proved to be consistent with four different BDT-based donor polymers, PTB7-Th, PBDB-T, J61, and TTFQx-T1. The highest performing devices are achieved with PTB7-Th and TTFQx-T1, with PCEs reaching 6.2 and 5.7%, respectively, when tetrahydrofuran solvent vapor annealing is combined with interfacial modification of the ZnO electron-transport layer.

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Section: Introductionmentioning

confidence: 99%

Toward a Universally Compatible Non‐Fullerene Acceptor: Multi‐Gram Synthesis, Solvent Vapor Annealing Optimization, and BDT‐Based Polymer Screening

et al. 2018

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“…The main electronic transition is often considered to be dominated by the HOMO → LUMO excitation. This assumption may be true when Δ H and Δ L are large enough, for example, thiophene ended DPP as central core with 1,3‐di‐ tert ‐butylbenzene as arms (CSDPP12) and merocyanine dyes . However, the situation may be completely different for molecules having small Δ H and Δ L , e.g., BDT and BDD based molecules.…”

Section: Resultsmentioning

confidence: 99%

“…Thus, a large number of the studied donor molecules have considerably small Δ H and Δ L values, and it is important to point out that the nearly degenerate occupied/unoccupied frontier orbitals of a donor molecule may be beneficial for the hole transport/exciton dissociation process, like the near degeneracy of LUMOs in acceptors enhances the exciton dissociation rate at the donor-acceptor interface. This assumption may be true when Δ H and Δ L are large enough, for example, thiophene ended DPP as central core with 1,3-di-tert-butylbenzene as arms (CSDPP12) [92] and merocyanine dyes. Poor correlation between these properties indicates that they can be considered as independent descriptors.…”

Section: Importance Of Orbitals Energetically Close To Frontier Orbitmentioning

confidence: 99%

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

Sahu

Rao

Troisi

et al. 2018

Advanced Energy Materials

206

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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“…OSCs based on these small molecules achieved moderate PCEs in the range of 2.86–3.55%. After the optimization with solvent and thermal annealing, the BHJ devices, based on a17d :PC 71 BM and a17e :PC 71 BM showed improved PCEs of 5.47% and 4.88%, respectively, which came from the improved charge‐carrier mobility, crystallinity, and light‐harvesting ability of the active layer …”

Section: Dpp‐based Photovoltaic Small Molecules As Electron Donorsmentioning

confidence: 99%

Design of Diketopyrrolopyrrole (DPP)‐Based Small Molecules for Organic‐Solar‐Cell Applications

et al. 2016

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After the first report in 2008, diketopyrrolopyrrole (DPP)-based small-molecule photovoltaic materials have been intensively explored. The power conversion efficiencies (PCEs) for the DPP-based small-molecule donors have been improved up to 8%. Furthermore, through judicious structure modification, DPP-based small molecules can also be converted into electron-acceptor materials, and, recently, some exciting progress has been achieved. The development of DPP-based photovoltaic small molecules is summarized here, and the photovoltaic performance is discussed in relation to structural modifications, such as the variations of donor-acceptor building blocks, alkyl substitutions, and the type of conjugated bridges, as well as end-capped groups. It is expected that the discussion will provide a guideline in the exploration of novel and promising DPP-containing photovoltaic small molecules.

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Influence of thermal and solvent annealing on the morphology and photovoltaic performance of solution processed, D–A–D type small molecule-based bulk heterojunction solar cells

Abstract: Four new small molecules CSDPP9–CSDPP12 were obtained with appended electron donating units in the molecular terminals of a DPP core. On solvent and thermal annealing, for the CSDPP11:PC71BM blend, the BHJ device displayed a PCE of 5.47%.

Cited by 12 publications

References 72 publications

Toward a Universally Compatible Non‐Fullerene Acceptor: Multi‐Gram Synthesis, Solvent Vapor Annealing Optimization, and BDT‐Based Polymer Screening

Toward a Universally Compatible Non‐Fullerene Acceptor: Multi‐Gram Synthesis, Solvent Vapor Annealing Optimization, and BDT‐Based Polymer Screening

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

Design of Diketopyrrolopyrrole (DPP)‐Based Small Molecules for Organic‐Solar‐Cell Applications

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