Triplet Tellurophene‐Based Acceptors for Organic Solar Cells

Yang, Lei; Gu, Wenxing; Lv, Lei; Chen, Yu‐Sheng; Yang, Yufei; Ye, Pan; Wu, Jianfei; Lei, Hong; Peng, Aidong; Huang, Hui

doi:10.1002/anie.201712011

Cited by 134 publications

(83 citation statements)

References 60 publications

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“…During charge migration, nongeminate (NG) or bimolecular recombination may occur; [ 6,7 ] this leads to the formation of CT excitons, with either singlet ( S CT) or triplet ( T CT) character in a 1:3 ratio following the spin statistics. [ 8 ] These nearly energetically degenerate S CT and T CT excitons will recombine or separate again into FC. The recombination of S CT to the ground state (S0) can be effectively suppressed because of the high enough S CT energy ( E CT ), according to the energy‐gap law (Figure S1a, Supporting Information).…”

Section: Figurementioning

confidence: 99%

Reducing the Singlet−Triplet Energy Gap by End‐Group π−π Stacking Toward High‐Efficiency Organic Photovoltaics

Han

2020

Advanced Materials

108

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S CT) or triplet ( T CT) character in a 1:3 ratio following the spin statistics. [8] These nearly energetically degenerate S CT and T CT excitons will recombine or separate again into FC. The recombination of S CT to the ground state (S0) can be effectively suppressed because of the high enough S CT energy (E CT ), according to the energygap law ( Figure S1a, Supporting Information). [9−12] Although the recombination from T CT to S0 is spin-forbidden, T CT can relax to the lower-lying triplet state (T1) on the material with lower S1 excitation energy (E S1 , which determines optical gap of the device, E g ) via back electron transfer (BET). [13−18] The singlet−triplet energy gap (ΔE ST = E S1 -E T1 , where E T1 is the T1 excitation energy) is usually very large (≈0.7 eV) in the organic π-conjugated molecules and polymers with strong optical absorption and emission. [19−21] If the CT driving force (ΔE CT = E S1 -E CT ) is small (as required to maximize open-circuit voltage, V OC ), the speed of T1 to thermalize back into T CT will be limited due to the large difference between E CT and E T1 (ΔE BET = E CT -E T1 , Figure S1b, Supporting Information); the decay of T1 to S0 via intersystem crossing (ISC) and tripletcharge annihilation can thus constitute a major terminal loss channel of photocurrent. [13−18] Therefore, in order to reduce both voltage loss and NG recombination, the ΔE ST needs to be minimized ( Figure 1b). [22,23] Here, we have investigated the critical role of end-group π−π stacking in reducing ΔE ST in the state-of-the-art narrowbandgap nonfullerene (NF) acceptors (ITIC, IT-4F, and Y6, [24−26] Figure 2a) by means of (time-dependent) density functional theory (TD)DFT calculations in combination with molecular dynamics (MD) simulations (see Supporting Information for details). Owing to a modest degree of intramolecular push−pull effect, these acceptors show moderate ΔE ST while large oscillator strength ( f, ≈3) in the isolated molecules. Importantly, the ΔE ST is further reduced to 0.3−0.4 eV in the end-group π−π stacking dimers that are frequently present in the films. Such small ΔE ST proves to be able to suppress the T1 decay even in the case of very low ΔE CT of 0.1−0.2 eV. Accordingly, high J SC (>20 mA cm −2 ) and fill factor (FF, 75-80%) as well as low ΔV OC (≈ 0.6 V) have been achieved simultaneously, leading to high power conversion efficiencies (PCEs) of 13-18% in the OPVs based on these acceptors. [25−40] In principle, the ΔE ST value is determined by the electron exchange energy. Normally, the S1 and T1 states are both To improve the power conversion efficiencies for organic solar cells, it is necessary to enhance light absorption and reduce energy loss simultaneously. Both the lowest singlet (S1) and triplet (T1) excited states need to energertically approach the charge-transfer state to reduce the energy loss in exciton dissociation and by triplet recombination. Meanwhile, the S1 energy needs to be decreased to broaden light absorption. Therefore, it is imperative to reduce the...

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Section: Figurementioning

confidence: 99%

Reducing the Singlet−Triplet Energy Gap by End‐Group π−π Stacking Toward High‐Efficiency Organic Photovoltaics

Han

2020

Advanced Materials

108

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“…[26] The tellurophene-based molecule S15c showed the maximum field-effect hole mobility of 1.8 cm 2 V À 1 s À 1 , demonstrating the great potential for OFET applications. [29] The transient photoluminescence spectra showed S17, S18, and S19 possessed different lifetime of 2.9 ms, 11.6 ms, and 24.4 ms, respectively, suggesting the efficient intersystem crossing due to the large spin orbital coupling. [27] It was observed that the optical bandgap narrowed down from DPP2T(BTh) 2 (S16a) to DPP2T (BSe) 2 (S16b) to DPP2T(BTe) 2 (S16c).…”

Section: Applications Of Tellurophene-based Small Moleculesmentioning

confidence: 93%

The Synthesis and Optoelectronic Applications for Tellurophene‐Based Small Molecules and Polymers

et al. 2019

ChemPhysChem

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Tellurophene-based small molecules and polymers have received great attentions owing to their applications in thin-film transistors, solar cells, and sensors. This article reviews the current progress of the synthesis and applications of tellurophene-based small molecules and polymers. The physico-chemical properties and optoelectronic applications of tellurophene-based materials are summarized and discussed. In the end, the challenges and outlook of tellurophene-based materials are presented.[a] X.

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“…The first triplet tellurophene-PDI based acceptor (BFPTP) possessed long exciton lifetime and diffusion distances for efficient exciton dissociation rather than recombination. Thus, the PBDB-T: BFPTP blended films delivered a PCE of 7.52% (Yang et al, 2018a ). A fused and twisted PDI derivative with twisted thieno[2,3-b]thiophene (TT) as linker (cis-PBI) was reported.…”

Section: Pdi Based Small Molecule Electron Acceptorsmentioning

confidence: 99%

Small-Molecule Electron Acceptors for Efficient Non-fullerene Organic Solar Cells

et al. 2018

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The development of organic electron acceptor materials is one of the key factors for realizing high performance organic solar cells. Compared to traditional fullerene acceptor materials, non-fullerene electron acceptors have attracted much attention due to their better optoelectronic tunabilities and lower cost as well as higher stability. Non-fullerene organic solar cells have recently experienced a rapid increase with power conversion efficiency of single-junction devices over 14% and a bit higher than 15% for tandem solar cells. In this review, two types of promising small-molecule electron acceptors are discussed: perylene diimide based acceptors and acceptor(A)-donor(D)-acceptor(A) fused-ring electron acceptors, focusing on the effects of structural modification on absorption, energy levels, aggregation and performances. We strongly believe that further development of non-fullerene electron acceptors will hold bright future for organic solar cells.

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Triplet Tellurophene‐Based Acceptors for Organic Solar Cells

Cited by 134 publications

References 60 publications

Reducing the Singlet−Triplet Energy Gap by End‐Group π−π Stacking Toward High‐Efficiency Organic Photovoltaics

Reducing the Singlet−Triplet Energy Gap by End‐Group π−π Stacking Toward High‐Efficiency Organic Photovoltaics

The Synthesis and Optoelectronic Applications for Tellurophene‐Based Small Molecules and Polymers

Small-Molecule Electron Acceptors for Efficient Non-fullerene Organic Solar Cells

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