Simultaneously Achieved High Open‐Circuit Voltage and Efficient Charge Generation by Fine‐Tuning Charge‐Transfer Driving Force in Nonfullerene Polymer Solar Cells

Tang, Ailing; Xiao, Bo; Wang, Yuming; Gao, Feng; Tajima, Kazuo; Bin, Haijun; Zhang, Zhiguo; Li, Yongfang; Wei, Zhixiang; Zhou, Erjun

doi:10.1002/adfm.201704507

Cited by 193 publications

(166 citation statements)

References 51 publications

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“…For homogeneous media, theory predicts a CT binding energy of around 400 meV, in clear contrast to the high external quantum efficiency (EQE) for photocurrent generation of many NFA‐containing devices. Several studies showed high EQE to be related to a larger driving force . This situation reminds of the “hot” dissociation model, where exciton dissociation creates a more loosely bound electronically/vibronically excited CT state .…”

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confidence: 72%

“…To determine the CT energy, we fitted the reduced EQE PV and EL spectra following the approach by Vandewal et al The resulting E CT = 1.41 eV is consistent with the value taken from the maximum of the derivative of the EQE PV curve, as also shown in Figure S4 (Supporting Information). Alternatively, we fitted only the low energy shoulder of the EL spectra using Marcus theory (as previously done in the work by Tang et al) which yields E CT = 1.29 eV. The singlet exciton energy of PM6 and Y6 were obtained from the crossing point of the absorption and photoluminescence (PL) spectra of the pristine films.…”

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confidence: 99%

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Barrierless Free Charge Generation in the High‐Performance PM6:Y6 Bulk Heterojunction Non‐Fullerene Solar Cell

et al. 2020

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Organic solar cells are currently experiencing a second golden age thanks to the development of novel non‐fullerene acceptors (NFAs). Surprisingly, some of these blends exhibit high efficiencies despite a low energy offset at the heterojunction. Herein, free charge generation in the high‐performance blend of the donor polymer PM6 with the NFA Y6 is thoroughly investigated as a function of internal field, temperature and excitation energy. Results show that photocurrent generation is essentially barrierless with near‐unity efficiency, regardless of excitation energy. Efficient charge separation is maintained over a wide temperature range, down to 100 K, despite the small driving force for charge generation. Studies on a blend with a low concentration of the NFA, measurements of the energetic disorder, and theoretical modeling suggest that CT state dissociation is assisted by the electrostatic interfacial field which for Y6 is large enough to compensate the Coulomb dissociation barrier.

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confidence: 72%

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confidence: 99%

Barrierless Free Charge Generation in the High‐Performance PM6:Y6 Bulk Heterojunction Non‐Fullerene Solar Cell

et al. 2020

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“…[10][11][12][13][14][15] Key and fundamental strategies for designing high-effciency nonfullerene PSC devices are absorption spectrum and energy level. [18,19] In addition, the most difficult and complicated problem is how to precisely modulate the microstructure of the blending system. [16,17] The matching energy levels are crucial for donor and acceptor to ensure efficient driving force of exciton dissociation, to minimize voltage loss and thus to guarantee high V OC .…”

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confidence: 99%

A Maverick Asymmetrical Backbone with Distinct Flanked Twist Angles Modulating the Molecular Aggregation and Crystallinity for High Performance Nonfullerene Solar Cells

Wang

Dou

et al. 2018

Advanced Energy Materials

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energy source. [1][2][3][4] The past few years have witnessed the rapid progress of nonfullerene n-type acceptors and the PCE of nonfullerene-based PSCs devices have already surpassed 13% for single-junction devices. [5][6][7][8][9] To achieve efficient nonfullerene PSCs and mature fully from research into cost effective products, it is of critical importance not only to design high-performance small molecular acceptors (SMAs), but also to develop matching donor polymers, as well as to deeply understand the mechanism of the coordinated microstructure interactions between donor and acceptor components. [10][11][12][13][14][15] Key and fundamental strategies for designing high-effciency nonfullerene PSC devices are absorption spectrum and energy level. The donor and acceptor components should possess complementary absorptions and high extinction coefficient to enhance light harvesting to achieve high J SC . [16,17] The matching energy levels are crucial for donor and acceptor to ensure efficient driving force of exciton dissociation, to minimize voltage loss and thus to guarantee high V OC . However, the troublesome tradeoff between high V OC and J SC is inevitable which is the big challenge for further improving the PSCs performance. [18,19] In addition, the most difficult and complicated problem is how to precisely modulate the microstructure of the blending system. The donor should exhibit good morphology compatibility with the acceptor, including suitable crystallinity, appropriate aggregation, face-on orientation, and moderate domain size, and thus to achieve excellent charge transport and high fill factor (FF). [20][21][22] Therefore, establishing universal and general guideline of rational designing compatible D/A structure is extremely urgent and important for nonfullerene PSCs.Benzo[1,2-b:4,5-b′]dithiophene (BDT) and dithieno[2,3d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene (DTBDT) are the dominant backbones for donor polymers because of their planar framework, showing the most high performance in PSCs. [23][24][25][26][27][28][29][30] Most researchers focus on the side chain engineering of BDT-and DTBDT-based polymers and demonstrate that optimized side-chain can easily control polymer packing In this work, a new asymmetrical backbone thienobenzodithiophene (TBD) containing four aromatic rings is designed, and then four polymers PTBD-BZ, PTBD-BDD, PTBD-FBT, and PTBD-Tz are synthesized. The planar and high degree of π-conjugation configuration can guarantee effective charge carrier transport and the distinct flanked dihedral angles between the TBD core and conjugated side chain can subtly regulate the molecular aggregation and crystallinity. The four polymer/3,9-bis(2-methylene-(3-(1,1dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]-dithiophene (ITIC) blending films exhibit predominantly face-on orientation. The photovoltaic devices based on wide bandgap polymers PTBD-BZ and PTBD-BDD achieve power conversion efficiencies (PCEs) as high as 12.02% and...

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“…Efficient charge separation is encouraged by having a small energetic offset (≈0.3 eV) between the LUMO of the ED and EA (Δ E LUMO in Figure a) and between HOMO of EA and ED (Δ E HOMO in Figure a). Conversely, some recent reports indicate that the HOMO/LUMO offset might not be necessary for FREA‐based OSCs and may also reduce charge transfer energy losses …”

Section: Osc Parameters and Architecturementioning

confidence: 94%

Recent Progress in Molecular Design of Fused Ring Electron Acceptors for Organic Solar Cells

Dey

2019

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135

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The quest for sustainable energy sources has led to accelerated growth in research of organic solar cells (OSCs). A solution‐processed bulk‐heterojunction (BHJ) OSC generally contains a donor and expensive fullerene acceptors (FAs). The last 20 years have been devoted by the OSC community to developing donor materials, specifically low bandgap polymers, to complement FAs in BHJs. The current improvement from ≈2.5% in 2013 to 17.3% in 2018 in OSC performance is primarily credited to novel nonfullerene acceptors (NFA), especially fused ring electron acceptors (FREAs). FREAs offer unique advantages over FAs, like broad absorption of solar radiation, and they can be extensively chemically manipulated to tune optoelectronic and morphological properties. Herein, the current status in FREA‐based OSCs is summarized, such as design strategies for both wide and narrow bandgap FREAs for BHJ, all‐small‐molecule OSCs, semi‐transparent OSC, ternary, and tandem solar cells. The photovoltaics parameters for FREAs are summarized and discussed. The focus is on the various FREA structures and their role in optical and morphological tuning. Besides, the advantages and drawbacks of both FAs and NFAs are discussed. Finally, an outlook in the field of FREA‐OSCs for future material design and challenges ahead is provided.

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Simultaneously Achieved High Open‐Circuit Voltage and Efficient Charge Generation by Fine‐Tuning Charge‐Transfer Driving Force in Nonfullerene Polymer Solar Cells

Cited by 193 publications

References 51 publications

Barrierless Free Charge Generation in the High‐Performance PM6:Y6 Bulk Heterojunction Non‐Fullerene Solar Cell

Barrierless Free Charge Generation in the High‐Performance PM6:Y6 Bulk Heterojunction Non‐Fullerene Solar Cell

A Maverick Asymmetrical Backbone with Distinct Flanked Twist Angles Modulating the Molecular Aggregation and Crystallinity for High Performance Nonfullerene Solar Cells

Recent Progress in Molecular Design of Fused Ring Electron Acceptors for Organic Solar Cells

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