Characterization and Distribution of Poly(3‐hexylthiophene) Phases in an Annealed Blend Film

Hu, Rong; Zhang, Wei; Wang, Peng; Qin, Yujun; Ran, Liang; Fu, Li‐Min; Zhang, Jianping; Ai, Xi-Cheng

doi:10.1002/cphc.201301147

Cited by 6 publications

(5 citation statements)

References 47 publications

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“…Before we discuss the transient absorption spectra for donor:acceptor blends, we identify the spectral features present in the annealed P3HT film, shown in Figure 5 . The negative feature between 400 and 610 nm corresponds to the ground state bleach (GSB) and is indicative of ordered crystalline P3HT, which is consistent with reported ordering of P3HT crystallites after thermal annealing . The broad absorption band at 610–1000 nm is due to the overlap of polaron absorption at 950 nm, polaron pair absorption at ≈650 nm, and stimulated emission (a negative contribution) at ≈700 nm .…”

Section: Resultssupporting

confidence: 83%

“…The negative feature between 400 and 610 nm corresponds to the ground state bleach (GSB) and is indicative of ordered crystalline P3HT, which is consistent with reported ordering of P3HT crystallites after thermal annealing. [35][36][37][38][39][40][41][42] Absorption due to singlet excitons appears as the broad feature at 1250 nm. [35][36][37][38][39][40][41][42] Absorption due to singlet excitons appears as the broad feature at 1250 nm.…”

Section: Ultrafast Transient Absorption Measurementsmentioning

confidence: 99%

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Inter‐Fullerene Electronic Coupling Controls the Efficiency of Photoinduced Charge Generation in Organic Bulk Heterojunctions

Larson

Reid

Coffey

et al. 2016

Advanced Energy Materials

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energy and (ii) equally efficient collection of those charges. The former relies on appropriate choice of donor and acceptor materials that balance minimal reorganization energy with optimally aligned energy levels, while the latter principally relies on high hole and electron mobilities in their respective phases. [1] Over the past decade, significant research efforts have been devoted to gaining a better fundamental understanding of the relationship between molecular properties and the photophysics of interfacial and bulk free charge generation and transport in OPV material systems, which has directly led to increases in the performance of these materials by rational design. [2][3][4][5][6] In the case of polymer:fullerene OPVs, the polymer acts as the dominant light absorber and also directs film morphology, which are two crucial tasks for an OPV material. Naturally, a greater amount of effort has gone into understanding how structural, electronic, and physicochemical properties of the polymer affect charge generation photophysics than has been expended for the fullerene. Nonetheless, these systems are inherently bipartite, and, as we show in this report, the properties of the fullerene acceptor should be as carefully considered as those of the polymer for maximizing free carrier generation.We are particularly interested in the question of how local electronic coupling between individual fullerene molecules affects photoinduced charge generation (PCG). Some of the present authors have addressed this question previously, modulating aggregation of either the polymer or the fullerene to control PCG. [7] Here, the electronically coupled donor aggregates (polythiophene crystals) are always present. We investigate the importance of local coupling between fullerenes in high-loading OPV blends containing more complicated bulk heterojunction (BHJ) structures and interfaces, i.e., -those relevant to working devices. The observed high-frequency electron mobility in the fullerene phase is taken as a qualitative measure of the local electronic coupling strength between fullerenes.From an experimental standpoint, this question has been extremely difficult to answer in bulk heterojunction structures because of the large number of variables contributing to PCG Photoinduced charge generation (PCG) dynamics are notoriously difficult to correlate with specific molecular properties in device relevant polymer:fullerene organic photovoltaic blend films due to the highly complex nature of the solid state blend morphology. Here, this study uses six judiciously selected trifluoromethylfullerenes blended with the prototypical polymer poly(3-hexylthiophene) and measure the PCG dynamics in 50 fs-500 ns time scales with time-resolved microwave conductivity and femtosecond transient absorption spectroscopy. The isomeric purity and thorough chemical characterization of the fullerenes used in this study allow for a detailed correlation between molecular properties, driving force, local intermolecular electronic coupling and, ultimately, the ...

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Section: Resultssupporting

confidence: 83%

Section: Ultrafast Transient Absorption Measurementsmentioning

confidence: 99%

Inter‐Fullerene Electronic Coupling Controls the Efficiency of Photoinduced Charge Generation in Organic Bulk Heterojunctions

Larson

Reid

Coffey

et al. 2016

Advanced Energy Materials

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“…This is expected since the typical P3HT or PCBM domain size measured for samples with similar preparations conditions is reported to be considerably smaller (e.g., nanoscale) than the diameter of the laser spot used to collect the Raman images . Absorption spectra are susceptible to changes in isolated, ordered and disordered phases of P3HT . Peaks at 550 and 600 nm are assigned to ordered phases, while peaks at higher energies correspond to isolated and disordered phases.…”

Section: Resultsmentioning

confidence: 94%

“…5 Absorption spectra are susceptible to changes in isolated, ordered and disordered phases of P3HT. 42 Peaks at 550 and 600 nm are assigned to ordered phases, while peaks at higher energies correspond to isolated and disordered phases. The Raman fwhm values (Table 1) and absorption spectra ( Figure 2), when normalized to account for differences in film thickness, show relative agreement on the degree of polymer order for the P3HT films prepared with different preparation conditions.…”

Section: 39−41mentioning

confidence: 99%

Quantitative Comparison of Organic Photovoltaic Bulk Heterojunction Photostability Under Laser Illumination

et al. 2014

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The photostability of bulk heterojunction organic photovoltaic films containing a polymer donor and a fullerene-derivative acceptor was examined using resonance Raman spectroscopy and controlled laser power densities. The polymer donors were poly(3-hexylthiophene-2,5-diyl) (P3HT), poly [[9-(1-octylnonylFour sample preparation methods were studied: (i) thin or (ii) thick films with fast solvent evaporation under nitrogen, (iii) thick films with slow solvent evaporation under nitrogen, and (iv) thin films dried under nitrogen followed by thermal annealing. Polymer order was assessed by monitoring a Raman peak's full width at half-maximum and location as a function of illumination time and laser power densities from 2.5 × 10 3 to 2.5 × 10 5 W cm −2. Resonance Raman spectroscopy measurements show that before prolonged illumination, PCDTBT and PTB7 have the same initial order for all preparation conditions, while P3HT order improves with slow solvent drying or thermal annealing. All films exhibited changes to bulk heterojunction structure with 2.5 × 10 5 Wcm −2 laser illumination as measured by resonance Raman spectroscopy, and atomic force microscopy images show evidence of sample heating that affects the polymer over an area greater than the illumination profile. Photostability data are important for proper characterization by techniques involving illumination and the development of devices suitable for real-world applications.

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“…As for the neat PBDTTT-E layer, it exhibits a main absorption band in the wavelength range of 500–800 nm with two absorption peaks at 680 and 626 nm. The former absorption peak is often referred to as the vibronic progression of the electronic state (0′-0), whereas the latter peak is considered as the (1′-0) vibronic absorption of electronic transition, and they both are in relation to the aggregation state of co-polymers ( Clark et al, 2009 ; Hu et al, 2014 ; Huo et al, 2014 ; Fauvell et al, 2016 ). Herein, the relative absorption intensity of the 626 nm peak of the neat PTB7 film ( A 1´-0 / A 0´-0 ) is slightly enhanced comparing with that of the PBDTTT-E film, suggesting that the fluorine substituent can influence the co-planar conformation and optical absorption of the polymer ( Leclerc et al, 1993 ; Huo et al, 2013 ).…”

Section: Resultsmentioning

confidence: 99%

Charge Photogeneration and Recombination in Fluorine-Substituted Polymer Solar Cells

Liu

Peng

et al. 2022

Front. Chem.

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In this contribution, we studied the effect of fluorine substitution on photogenerated charge generation, transport, and recombination in polymer solar cells. Two conjugated polymer materials, PBDTTT-E (fluorine free) and PTB7 (one fluorine substitution), were compared thoroughly. Meanwhile, various characterization techniques, including atomic force microscopy, steady-state spectroscopy, transient absorption spectroscopy, spectroelectrochemistry, and electrical measurements, were employed to analyse the correlation between molecular structure and device performance. The results showed that the influence of fluorine substitution on both the exciton binding energy of the polymer and the carrier recombination dynamics in the ultrafast timescale on the polymer was weak. However, we found that the fluorine substitution could enhance the exciton lifetime in neat polymer film, and it also could increase the mobility of photogenerated charge. Moreover, it was found that the SOMO energy level distribution of the donor in a PTB7:PC71BM solar cell could facilitate hole transport from the donor/acceptor interface to the inner of the donor phase, showing a better advantage than the PBDTTT-E:PC71BM solar cell. Therefore, fluorine substitution played a critical role for high-efficiency polymer solar cells.

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Characterization and Distribution of Poly(3‐hexylthiophene) Phases in an Annealed Blend Film

Cited by 6 publications

References 47 publications

Inter‐Fullerene Electronic Coupling Controls the Efficiency of Photoinduced Charge Generation in Organic Bulk Heterojunctions

Inter‐Fullerene Electronic Coupling Controls the Efficiency of Photoinduced Charge Generation in Organic Bulk Heterojunctions

Quantitative Comparison of Organic Photovoltaic Bulk Heterojunction Photostability Under Laser Illumination

Charge Photogeneration and Recombination in Fluorine-Substituted Polymer Solar Cells

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