Solvent‐Polarity‐Induced Active Layer Morphology Control in Crystalline Diketopyrrolopyrrole‐Based Low Band Gap Polymer Photovoltaics

Ferdous, Sunzida; Liu, Feng; Wang, Dong; Russell, Thomas P.

doi:10.1002/aenm.201300834

Cited by 30 publications

(21 citation statements)

References 30 publications

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“…The XRD patterns of all the films show distinct diffraction peaks at 2θ = 24.5 °C, which corresponds to the d‐spacing of 3.63 Å for π–π stacking of PThBDTP . DIO generally improves crystallinity of polymer materials in the film fabrication process, and thereby enhance carrier transport, leading to device efficiency improvement . The similar crystallinity of the films is consistent with their almost identical device performance.…”

Section: Parameters Of the Pthbdtp:pc71bm Devices Without/with Varioumentioning

confidence: 99%

Additive‐Free Organic Solar Cells with Power Conversion Efficiency over 10%

Mao

et al. 2017

Advanced Energy Materials

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selection, [13,14] thermal annealing, [15,16] and solvent annealing. [13,17] In recent work, a variety of liquid additives, including 1,8-octanedithiol, [18] 1,8-diiodooctane (DIO), [19,20] nitrobenzene, [21] N-methylpyrrolidone, [22,23] chloronapthalene, [24] etc. have been introduced into the D/A blend. These additives successfully manipulated the nanomorphology of the active layer and markedly increased the efficiency of OSCs. Among these additives, DIO was the most used and also very effective one, power conversion efficiencies (PCEs) of over 10% have already been realized with the help of DIO in single-layer OSCs. [2][3][4][5][6][7][8] However, optimizing the ratio of additive in the parent solvent is a tedious process, and the additive also deteriorates the reproducibility of the device performance (PCE of the device is very sensitive to DIO ratio variation; the slow drying process of the residual high-boiling-point additive in the active layer could induce undesirable morphological change). [25] What's worse, residual DIO also greatly accelerates the photo-oxidative degradation by acting as a radial initiator and dramatically decreases the lifetime of the device. [26,27] To remove DIO in the film, several methods have been tried such as putting the film in high-vacuum environment, annealing the film at high temperature [26] and washing the film with methanol. [25] However, all these cannot root out the problem that DIO brings in: the high vacuum technique is not amenable to large scale manufacturing process, such as roll-to-roll. The high temperature annealing deteriorates the performance of most high-efficiency OSCs, such as PTB7-Th based ones, [28,29] and may be incompatible with the flexible substrates as well, such as poly(ethylene terephthalate). [30] Thereby, materials that can be processed with simple and reliable procedures which do not require additive addition and active layer post treatments (thermal annealing, solvent annealing, and surface modification) are urgently required. In this regard, several donor and acceptor materials have been tried. For example, Lin et al. employed a new acceptor ITIC-Th in fullerene-free solar cells and got a PCE of 7.5%, [31] Yue et al. designed a novel polymer donor TBTIT-h in OSCs and gained a PCE of 9.1%, [32] Zhang et al. applied a new polymer PBDT-TS1 in OSCs and realized a PCE of 9.67%. [33] In this paper, we utilized a D-A copolymer PThBDTP (consisting of a thiophene as the donor and BDTP as the acceptor unit), [34] and achieved a PCE of 10.06% based on the PThBDTP:PC 71 BM blend. As far as we know, such efficiency is the highest for those additive-free and post treatment free OSCs. Nowadays, solvent additives are widely used in organic solar cells (OSCs) to tune the nano-morphology of the active blend film and enhance the device performance. With their help, power conversion efficiencies (PCEs) of OSCs have recently stepped over 10%. However, residual additive in the device can induce undesirable morphological change and also accelerate photo-oxidation de...

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Section: Parameters Of the Pthbdtp:pc71bm Devices Without/with Varioumentioning

confidence: 99%

Additive‐Free Organic Solar Cells with Power Conversion Efficiency over 10%

Mao

et al. 2017

Advanced Energy Materials

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“…26,[29][30][31] Therefore, the use of those high bp solvents to improve D-A polymer-based OTFT performances would be beneficial. However, it is difficult to form high quality polymer films by spin-coating such high bp solutions onto hydrophobic gate dielectric surfaces, such as ODTS-treated SiO 2 gate dielectrics.…”

Section: Introductionmentioning

confidence: 99%

Low-Band-Gap Polymer-Based Ambipolar Transistors and Inverters Fabricated Using a Flow-Coating Method

et al. 2016

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The performances of organic thin film transistors (OTFTs) produced by polymer solution casting are tightly correlated with the morphology and chain-ordering of semiconducting polymer layers, which depends on the processing conditions applied. The slow evaporation of a high boiling point (bp) solvent permits sufficient time for the assembly of polymer chains during the process, resulting in improving the film crystallinity and inducing favorable polymer chain orientations for charge transport. The use of high bp solvents, however, often results in de-wetting of thin films formed on hydrophobic surfaces, such as the commonly used octadecyltrichlorosilane (ODTS)-treated SiO 2 gate dielectric. De-wetting hampers the formation of uniform and highly crystalline semiconducting active channel layers. In this manuscript, we demonstrated the formation of highly crystalline dithienothienyl diketopyrrolopyrrole (TT-DPP)-based polymer films using a flow-coating method to enable the fabrication of ambipolar transistors and inverters.Importantly, unlike conventional spin-coating methods, the flow-coating method allowed us to use high bp solvents, even on a hydrophobic surface, and minimized the polymer solution waste. The crystalline orientations of the TT-DPP-based polymers were tuned depending on the solvent used (four different bp solvents were tested) and the employment of a thermal annealing step. The use of high bp solvents and thermal annealing of the polymer films significantly enhanced the crystalline microstructures in the flowcoated films, resulting in considerable carrier mobility increase in the OTFTs compared to the spin-coated films. Our simple, inexpensive, and scalable flow-coating method, for the first time employed in printing semiconducting polymers, presents a significant step toward optimizing the electrical performances of organic ambipolar transistors through organic semiconducting layer film crystallinity engineering.

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“…Performance of many bulk heterojunction organic solar cells can be greatly increased upon annealing of the active layer or when processed with high boiling point additives . This enhancement in the device performance is associated with more favorable morphology of donor–acceptor blends, which is characterized by a greater percolation network and a higher degree of crystallinity of donor material as compared to as‐cast films .…”

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confidence: 99%

Temperature Dependence of Exciton Diffusion in a Small‐Molecule Organic Semiconductor Processed With and Without Additive

et al. 2015

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The temperature dependence of exciton diffusion in a small-molecule organic semiconductor processed with and without additive is investigated. As-cast and 1,8-diiodooctane-processed films yield exciton diffusion lengths of 6.8 and 4.9 nm, respectively. Using a Monte Carlo simulation, it is shown that processing with 1,8-diiodooctane increases the excitonic trap density, which directly reduces the exciton diffusion length.

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Solvent‐Polarity‐Induced Active Layer Morphology Control in Crystalline Diketopyrrolopyrrole‐Based Low Band Gap Polymer Photovoltaics

Cited by 30 publications

References 30 publications

Additive‐Free Organic Solar Cells with Power Conversion Efficiency over 10%

Additive‐Free Organic Solar Cells with Power Conversion Efficiency over 10%

Low-Band-Gap Polymer-Based Ambipolar Transistors and Inverters Fabricated Using a Flow-Coating Method

Temperature Dependence of Exciton Diffusion in a Small‐Molecule Organic Semiconductor Processed With and Without Additive

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