Structural insights into Lewis acid- and F4TCNQ-doped conjugated polymers by solid-state magnetic resonance spectroscopy

Dixon, Alana L.; Vezin, Hervé; Nguyen, Thuc‐Quyen; Reddy, G. N. Manjunatha

doi:10.1039/d1mh01574e

Cited by 18 publications

(13 citation statements)

References 74 publications

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“…Solid-state NMR spectroscopy probes information on inter- and intramolecular interactions at sub-nanometer to nanometer distances, making it a powerful tool to understand local structure, molecular conformation, and self-assembly by probing close proximity interactions between donor and acceptor molecules in OSC BHJs. ,− A priori, signal component analysis of model compounds and neat donor polymers provides key insight into the conformational differences in the backbone and side chain structure. Here, we first examine 1 H, 13 C and 19 F sites in a model PTQ10 discrete molecule, PTQ10, and PTQ10 90:10 using 1D and 2D ssNMR techniques. − The model PTQ10 molecule was designed as a single PTQ10 segment and consists of a quinoxaline ring flanked with thiophene units capped with methyl groups in the thiophene five position. It is important to note that the alkoxy side chain is shorter, 2-ethylhexyloxy, on the discrete molecule to ensure it was a solid.…”

Section: Resultsmentioning

confidence: 99%

Insights into the Local Bulk-Heterojunction Packing Interactions and Donor–Acceptor Energy Level Offsets in Scalable Photovoltaic Polymers

Jones

Schneider

et al. 2022

Chem. Mater.

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An energy level offset in organic solar cells (OSCs) is necessary for efficient charge generation and separation. To date, there are several polymer donor−non-fullerene acceptor (NFA) bulk-heterojunction (BHJ) systems with a negligible ionization energy (IE) level offset achieving high power conversion efficiencies (PCEs) over 15%. Although these donor−acceptor pairs perform well in solar cells, there is little understanding on why some systems can achieve this phenomenon, and therefore, many of these BHJs are discovered through a trial-and-error process. Here, we investigate how OSC efficiencies can be modulated by adjusting the IE level offset in a series of PTQ10 n:m random terpolymer donors by means of solar cell performance (open circuit voltage (V OC ) and short-circuit current (J SC )) when paired with Y6 and IDIC acceptors. PTQ10's IE level was adjusted through a copolymerization of thiophene (n), bithiophene (m), and quinoxaline monomer units in different ratios, whereby 10% bithiophene leads to a 0.05 eV decrease in the polymer's IE. The incorporation of 10% bithiophene (PTQ10 90:10) led to a 1.3 ± 0.5 mA/cm 2 increase in J SC when paired with Y6 (PCE = 13.8 ± 0.4%) in conjunction with an incremental decrease in V OC and fill factor (FF) when compared to PTQ10 (PCE = 14.7 ± 0.1%). Increasing the bithiophene content to 20% (PTQ10 80:20) exacerbated the decrease in V OC and FF further without the benefit of increased J SC . The drop in FF with increasing bithiophene incorporation correlated with increasing edge-on orientation in the neat polymer and polymer:Y6 BHJ blend films, shown by grazing-incidence wide-angle X-ray scattering measurements. High-field solidstate (ss)NMR spectroscopy analysis of single component PTQ10, Y6, and PTQ10:Y6 BHJ blends provides a complementary insight into how a low IE level offset system (PTQ10:Y6) imparts high performance. By resolving inter-and intramolecular packing interactions at sub-nanometer distances, ssNMR results offer key insights into the changes in local structures and conformations in the vicinity of the alkoxy PTQ10 side chains and in the Y6 end group in BHJ blends when compared to the neat compounds. Despite the changes in local structures, the BHJ morphology maintains pure D-A domains and preserves the microstructure, which correlates with the high-performing solar cells. A synergic combination of chemical design, multiscale morphology characterization, and device physics shown in this study provides an excellent strategy to investigate the BHJ and its role in organic solar cell performance.

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Section: Resultsmentioning

confidence: 99%

Insights into the Local Bulk-Heterojunction Packing Interactions and Donor–Acceptor Energy Level Offsets in Scalable Photovoltaic Polymers

Jones

Schneider

et al. 2022

Chem. Mater.

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“…The SSNMR results indeed establish the molecular origins for the different optoelectronic properties, which are due to the different degrees of D‐A intermix and local domain separation for the PM2:ITIC‐Th and PM2:PC 61 BM blends, consistently with the recent SSNMR studies of organic semiconductors and BHJ blends. [ 45,65–67 ]…”

Section: Discussionmentioning

confidence: 99%

Low Voltage‐Loss Organic Solar Cells Light the Way for Efficient Semitransparent Photovoltaics

Luginbuhl

Ran

et al. 2022

Solar RRL

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Organic solar cells that are transparent to visible light are highly desirable for applications such as window treatments or solar greenhouse panels. A key challenge is to simultaneously transmit most photons between 400 and 700 nm while retaining a high short‐circuit current and power conversion efficiency (PCE). Here, organic bulk heterojunction (BHJ) solar cells consisting of a donor polymer (PM2) is reported and the non‐fullerene acceptor ITIC‐Th achieves a PCE of 9.3%, and the BHJ thin films exhibit an average visible transmittance over 40%. This value is achieved primarily due to a very high open‐circuit voltage (VOC) of 0.93 V, which represents a voltage loss of only 0.50 V relative to the material optical bandgap, Eopt. In PM2:PC61BM devices, this voltage loss increases to 0.62 V (VOC = 0.82 V). It is found that this difference in VOC is due to higher nonradiative recombination in the fullerene‐based solar cell, suggesting that non‐fullerene acceptors may lead to better performance in semi‐transparent devices. The optoelectronic properties associated with PM2:ITIC‐Th and PM2:PC61BM blends are further corroborated by different morphological features and local structures at the donor‐acceptor interfaces characterized by atomic force microscopy, X‐ray scattering, and solid‐state NMR spectroscopy techniques.

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“…The presence of excess dopants and dopant aggregates unduly disrupts the nanostructure of the semiconductor, which tends to negatively affect the electrical properties. 9 − 11 …”

Section: Introductionmentioning

confidence: 99%

“…The ionization efficiency is reduced to less than 100% in the case that only partial charge transfer occurs, if there is an unfavorable energetic offset between EA dopant and IE semiconductor or if the dopant molecules aggregate. The presence of excess dopants and dopant aggregates unduly disrupts the nanostructure of the semiconductor, which tends to negatively affect the electrical properties. − …”

Section: Introductionmentioning

confidence: 99%

Double Doping of a Low-Ionization-Energy Polythiophene with a Molybdenum Dithiolene Complex

et al. 2022

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Doping of organic semiconductors is crucial for tuning the charge-carrier density of conjugated polymers. The exchange of more than one electron between a monomeric dopant and an organic semiconductor allows the polaron density to be increased relative to the number of counterions that are introduced into the host matrix. Here, a molybdenum dithiolene complex with a high electron affinity of 5.5 eV is shown to accept two electrons from a polythiophene that has a low ionization energy of 4.7 eV. Double p-doping is consistent with the ability of the monoanion salt of the molybdenum dithiolene complex to dope the polymer. The transfer of two electrons to the neutral dopant was also confirmed by electron paramagnetic resonance spectroscopy since the monoanion, but not the dianion, of the molybdenum dithiolene complex features an unpaired electron. Double doping allowed an ionization efficiency of 200% to be reached, which facilitates the design of strongly doped semiconductors while lessening any counterion-induced disruption of the nanostructure.

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Structural insights into Lewis acid- and F4TCNQ-doped conjugated polymers by solid-state magnetic resonance spectroscopy

Abstract: Molecular doping strategies facilitate orders of magnitudes enhancements in the charge carrier mobility of organic semiconductors (OSCs). Understanding the mechanisms of different doping strategies for OSCs and molecular-level constraints on...

Cited by 18 publications

References 74 publications

Insights into the Local Bulk-Heterojunction Packing Interactions and Donor–Acceptor Energy Level Offsets in Scalable Photovoltaic Polymers

Insights into the Local Bulk-Heterojunction Packing Interactions and Donor–Acceptor Energy Level Offsets in Scalable Photovoltaic Polymers

Low Voltage‐Loss Organic Solar Cells Light the Way for Efficient Semitransparent Photovoltaics

Double Doping of a Low-Ionization-Energy Polythiophene with a Molybdenum Dithiolene Complex

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