17 Sep 15:32
Chem. Sci., 2019, 10,8348-8353
DOI: 10.1039/C9SC03504D, Edge Article
Open Access
Ruiping Zhang, Yuling Xu, Yi Zhang, Hyeong Seok Kim, Amit Sharma, Jing Gao, Guangfu Yang, Jong Seung Kim, Yao Sun
Theranostic nanoprobes (SYL NPs) prepared from a newly designed NIR-II fluorophore and FDA approved DSPE-mPEG5000 were well tolerated and exhibited multifunctional potential in diagnosis (photoacoustic & fluorescence imaging) and phototherapy in animal models.
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12 Aug 03:50
by Xiaopeng Xu,
Kui Feng,
Zhaozhao Bi,
Wei Ma,
Guangjun Zhang,
Qiang Peng
A platinum(II) complexation strategy is developed to regulate the crystallinity of a newly designed s‐tetrazine‐containing wide‐bandgap copolymer donor PSFTZ, and optimize the morphology of the PSFTZ:Y6 active blend film, which boosts successfully the power conversion efficiency of the resulting nonfullerene polymer solar cells (NF‐PSCs) from 13.03% to 16.35%. 16.35% is the new record for single‐junction NA‐PSCs at present.
Abstract
A new strategy of platinum(II) complexation is developed to regulate the crystallinity and molecular packing of polynitrogen heterocyclic polymers, optimize the morphology of the active blends, and improve the efficiency of the resulting nonfullerene polymer solar cells (NF‐PSCs). The newly designed s‐tetrazine (s‐TZ)‐containing copolymer of PSFTZ (4,8‐bis(5‐((2‐butyloctyl)thio)‐4‐fluorothiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐3,6‐bis(4‐octylthiophen‐2‐yl)‐1,2,4,5‐tetrazine) has a strong aggregation property, which results in serious phase separation and large domains when blending with Y6 ((2,2′‐((2Z,2′Z)‐((12,13‐bis(2‐ethylhexyl)‐3,9‐diundecyl‐12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2‐g]thieno[2′,3′:4,5]thieno[3,2‐b]indole‐2,10‐diyl)bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile)), and produces a power‐conversion efficiency (PCE) of 13.03%. By adding small amount of Pt(Ph)2(DMSO)2 (Ph, phenyl and DMSO, dimethyl sulfoxide), platinum(II) complexation would occur between Pt(Ph)2(DMSO)2 and PSFTZ. The bulky benzene ring on the platinum(II) complex increases the steric hindrance along the polymer main chain, inhibits the polymer aggregation strength, regulates the phase separation, optimizes the morphology, and thus improves the efficiency to 16.35% in the resulting devices. 16.35% is the highest efficiency for single‐junction PSCs reported so far.
08 Aug 05:54
by Saghar Masoomi‐Godarzi,
Maning Liu,
Yasuhiro Tachibana,
Valerie D. Mitchell,
Lars Goerigk,
Kenneth P. Ghiggino,
Trevor A. Smith,
David J. Jones
Liquid crystallinity is used in self‐assembly of materials designed to support intramolecular singlet fission (SF). Amorphous thin films of FHBC(TDPP)2 show no long‐range order, however, 150% triplet yields are measured. Triplet yields are increased to 170% in hexagonally packed discotic liquid crystalline films formed after thermal annealing. The thienyl substituted diketopyrrolopyrrole (TDPP) triplet hosts show no local order.
Abstract
Solution and solution‐deposited thin films of the discotic liquid crystalline electron acceptor–donor–acceptor (A‐D‐A) p‐type organic semiconductor FHBC(TDPP)2, synthesized by coupling thienyl substituted diketopyrrolopyrrole (TDPP) onto a fluorenyl substituted hexa‐peri‐hexabenzocoronene (FHBC) core, are examined by ultrafast and nanosecond transient absorption spectroscopy, and time‐resolved photoluminescence studies to examine their ability to support singlet fission (SF). Grazing incidence wide‐angle X‐ray (GIWAX) studies indicate that as‐cast thin films of FHBC(TDPP)2 are “amorphous,” while hexagonal packed discotic liquid crystalline films evolve during thermal annealing. SF in as‐cast thin films is observed with an ≈150% triplet generation yield. Thermally annealing the thin films improves SF yields up to 170%. The as‐cast thin films show no long‐range order, indicating a new class of SF material where the requirement for local order and strong near neighbor coupling has been removed. Generation of long‐lived triplets (µs) suggests that these materials may also be suitable for inclusion in organic solar cells to enhance performance.
03 Aug 11:06
by Jia-An Lin†?, Shu-Wei Li†?, Zong-Ying Liu†?, Deng-Gao Chen†, Chun-Ying Huang†, Yu-Chen Wei†, Yi-Yun Chen†, Zheng-Hua Tsai‡, Chun-Yuan Lo†, Wen-Yi Hung*‡, Ken-Tsung Wong*†§, and Pi-Tai Chou*†
Chemistry of Materials
DOI: 10.1021/acs.chemmater.9b02712
02 Aug 07:42
by Patrick E. Schneider, Fabijan Pavos?evic´, and Sharon Hammes-Schiffer*
The Journal of Physical Chemistry Letters
DOI: 10.1021/acs.jpclett.9b01803
30 Jul 03:49
by Francis Lin†‡, Lijian Zuo‡, Ke Gao‡, Ming Zhang§, Sae Byeok Jo‡, Feng Liu*§, and Alex K.-Y. Jen*†‡?
Chemistry of Materials
DOI: 10.1021/acs.chemmater.9b01242
27 Jul 16:26
by Zhenyin Hai*†‡, Mohammad Karbalaei Akbari†‡, Zihan Wei†‡, Jasper Zuallaert§?, Wesley De Neve§?, Chenyang Xue?, Hongyan Xu#, Francis Verpoort¶?, and Serge Zhuiykov*†‡
ACS Applied Materials & Interfaces
DOI: 10.1021/acsami.9b06555
27 Jul 16:26
by Junwoo Lee,
Jae Won Kim,
Sang Ah Park,
Sung Yun Son,
Kyoungwon Choi,
Woojin Lee,
Minjun Kim,
Jin Young Kim,
Taiho Park
When crosslinking and nonfullerene acceptors are introduced in organic photovoltaics, the burn‐in loss due to thermal aging and light soaking is dramatically suppressed because of the frozen morphology and high miscibility of the acceptor. The resulting crosslinked device shows 9.4% power conversion efficiency, which is the highest value reported to date for crosslinked active materials, in the first green processing approach.
Abstract
This work deals with the investigation of burn‐in loss in ternary blended organic photovoltaics (OPVs) prepared from a UV‐crosslinkable semiconducting polymer (P2FBTT‐Br) and a nonfullerene acceptor (IEICO‐4F) via a green solvent process. The synthesized P2FBTT‐Br can be crosslinked by UV irradiation for 150 s and dissolved in 2‐methylanisole due to its asymmetric structure. In OPV performance and burn‐in loss tests performed at 75 °C or AM 1.5G Sun illumination for 90 h, UV‐crosslinked devices with PC71BM show 9.2% power conversion efficiency (PCE) and better stability against burn‐in loss than pristine devices. The frozen morphology resulting from the crosslinking prevents lateral crystallization and aggregation related to morphological degradation. When IEICO‐4F is introduced in place of a fullerene‐based acceptor, the burn‐in loss due to thermal aging and light soaking is dramatically suppressed because of the frozen morphology and high miscibility of the nonfullerene acceptor (18.7% → 90.8% after 90 h at 75 °C and 37.9% → 77.5% after 90 h at AM 1.5G). The resulting crosslinked device shows 9.4% PCE (9.8% in chlorobenzene), which is the highest value reported to date for crosslinked active materials, in the first green processing approach.
26 Jul 12:31
by Olle Ingana¨s*
Chemistry of Materials
DOI: 10.1021/acs.chemmater.9b01220
26 Jul 12:31
by Hua Geng†‡, Lingyun Zhu?, Yuanping Yi*‡, Daoben Zhu‡, and Zhigang Shuai*§‡
Chemistry of Materials
DOI: 10.1021/acs.chemmater.9b01545
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26 Jul 12:31
by Qisheng Tu†‡, Yunlong Ma†, Xiaobo Zhou§, Wei Ma§, and Qingdong Zheng*†
Chemistry of Materials
DOI: 10.1021/acs.chemmater.9b02355
26 Jul 12:03
by Lijian Zuo,
Xueliang Shi,
Weifei Fu,
Alex K.‐Y. Jen
A semitransparent photovoltaic (ST‐PV) with a tandem architecture and selective absorption in invisible regions is designed. By developing highly efficient active layers that selective absorb in the UV and near‐infrared regions and designing an appropriate interconnecting layer and transparent electrode, the resulting tandem ST‐PV device exhibits light utilization efficiency of 5.7% with averaged visible transmittance (AVT) of 52.9% and power conversion efficiency up to 10.7%.
Abstract
Semitransparent (ST) photovoltaics (PVs) with selective absorption in the UV or/and near‐infrared (NIR) range(s) and reduced energy losses, are critical for high‐efficiency solar‐window applications. Here, a high‐performance tandem ST‐PV with selected absorption in the desirable regions of the solar spectrum is demonstrated. An ultralarge‐bandgap perovskite film (FAPbBr2.43Cl0.57, E
g ≈ 2.36 eV) is first developed to fulfil efficient selective absorption in the UV region. After optimization, the corresponding ST single junction (SJ) PV exhibits an averaged transmittance (AVT) of ≈68% and an efficiency of ≈7.5%. By sequentially reducing the visible absorbing component in a low‐bandgap organic bulk‐heterojunction layer, an ST‐PV with selective absorption in the NIR is achieved with a power conversion efficiency (PCE) of 5.9% and a high AVT of 62%. The energy loss associated with the SJ ST‐PVs is further reduced with a tandem architecture, which affords a high PCE of 10.7%, an AVT of 52.91%, and a light utilization efficiency up to 5.66%. These results represent the best balance of AVT and PCE among all ST‐PVs reported so far, and this design should pave the road for solar windows of high performance.
25 Jul 15:47
by Xiaofu Wu†, Weijie Wang†‡, Hao Hang†§, Hua Li†‡, Yonghong Chen†§, Qian Xu?, Hui Tong*†‡, and Lixiang Wang*†‡
ACS Applied Materials & Interfaces
DOI: 10.1021/acsami.9b08017
25 Jul 01:33
by Joachim Vollbrecht,
Viktor V. Brus,
Seo‐Jin Ko,
Jaewon Lee,
Akchheta Karki,
David Xi Cao,
Kilwon Cho,
Guillermo C. Bazan,
Thuc‐Quyen Nguyen
A comprehensive analytical model capable of quantifying bimolecular, bulk and surface trap‐assisted contributions to the overall nongeminate recombination losses in organic solar cells is reported. Common techniques such as light intensity‐dependent current density–voltage characteristics, capacitance spectroscopy, and open‐circuit voltage decay yield the necessary experimental data to successfully apply this analytical model.
Abstract
In this study, a comprehensive analytical model to quantify the total nongeminate recombination losses, originating from bimolecular as well as bulk and surface trap‐assisted recombination mechanisms in nonfullerene‐based bulk heterojunction organic solar cells is developed. This proposed model is successfully employed to obtain the different contributions to the recombination current of the investigated solar cells under different illumination intensities. Additionally, the model quantitatively describes the experimentally measured open‐circuit voltage versus light intensity dependence. Most importantly, it is possible to calculate the experimental results with the same fitting parameter values from the presented model. The validity of this model is also proven by a combination of other independent, steady‐state, and transient experimental techniques. This new powerful analytical tool will enable researchers in the photovoltaic community to take into account the synergetic contribution from all relevant types of nongeminate recombination losses in different optoelectronic systems and target their analysis of recombination dynamics at any operating voltage.
25 Jul 01:32
by Katie D. Rosenthal,
Michael P. Hughes,
Benjamin R. Luginbuhl,
Niva A. Ran,
Akchheta Karki,
Seo‐Jin Ko,
Huawei Hu,
Ming Wang,
Harald Ade,
Thuc‐Quyen Nguyen
This work reports a strategy that ensures the degree of nonradiative recombination can be measured accurately in low‐energetic‐offset organic photovoltaic systems and reports key observations on the relationship between the nonradiative recombination loss and properties of the donor/acceptor interface, including an observed correlation between high domain purity and high nonradiative recombination loss.
Abstract
Open‐circuit voltage (V
OC) losses in organic photovoltaics (OPVs) inhibit devices from reaching V
OC values comparable to the bandgap of the donor–acceptor blend. Specifically, nonradiative recombination losses (∆V
nr) are much greater in OPVs than in silicon or perovskite solar cells, yet the origins of this are not fully understood. To understand what makes a system have high or low loss, an investigation of the nonradiative recombination losses in a total of nine blend systems is carried out. An apparent relationship is observed between the relative domain purity of six blends and the degree of nonradiative recombination loss, where films exhibiting relatively less pure domains show lower ∆V
nr than films with higher domain purity. Additionally, it is shown that when paired with a fullerene acceptor, polymer donors which have bulky backbone units to inhibit close π–π stacking exhibit lower nonradiative recombination losses than in blends where the polymer can pack more closely. This work reports a strategy that ensures ∆V
nr can be measured accurately and reports key observations on the relationship between ∆V
nr and properties of the donor/acceptor interface.
25 Jul 01:32
by Kun Li,
Yishi Wu,
Yabing Tang,
Ming‐Ao Pan,
Wei Ma,
Hongbing Fu,
Chuanlang Zhan,
Jiannian Yao
A ternary material system–enabled 16.5% efficiency fullerene‐free organic photovoltaic cell is designed with a structurally similar higher‐LUMO‐level guest nonfullerene acceptor. The homogeneous fine morphology and the π–π stacking pattern enable the two acceptors to synergize, obtaining increased open‐circuit voltage, short‐circuit current, and fill factor.
Abstract
Ternary approaches to solar cell design utilizing a small bandgap nonfullerene acceptor as the near infrared absorber to increase the short‐circuit current density always decreases the open‐circuit voltage. Herein, a highly efficient polymer solar cell with an impressive efficiency of 16.28 ± 0.20% enabled by an effective voltage‐increased ternary blended fullerene‐free material approach is reported. In this approach, the structural similarity between the host and the higher‐LUMO‐level guest enables the two acceptors to be synergized, obtaining increased open‐circuit voltage and fill factor and a small increase of short‐circuit current density. The same beneficial effects are demonstrated by using two host binary systems. The homogeneous fine film morphologies and the π–π stacking patterns of the host blend are well maintained, while larger donor and acceptor phases and increased lamellar crystallinity, increased charge mobilities, and reduced monomolecular recombination can be achieved upon addition of the guest nonfullerene acceptor. The increased charge mobilities and reduced monomolecular recombination not only contribute to the improved fill factor but also enable the best devices to be fabricated with a relatively thicker ternary blended active layer (110 vs 100 nm). This, combined with the absorption from the added guest acceptor, contribute to the increased short‐circuit current.
25 Jul 01:30
by E´tienne Rochette*, Vincent Desrosiers, Yashar Soltani, and Fre´de´ric-Georges Fontaine*
Journal of the American Chemical Society
DOI: 10.1021/jacs.9b04305
24 Jul 03:25
by Zong Cheng, Zhiqiang Li, Yincai Xu, Jixiong Liang, Chunhui Lin, Jinbei Wei*, and Yue Wang*
ACS Applied Materials & Interfaces
DOI: 10.1021/acsami.9b07820
24 Jul 03:25
by Ya Liu†‡, Kepeng Chen§, Songqiu Yang†, Daoyuan Zheng†‡, Guanghua Ren†‡, Yang Yang†, Jianzhang Zhao§, Donghui Wei?, and Keli Han*†?
The Journal of Physical Chemistry Letters
DOI: 10.1021/acs.jpclett.9b01454
23 Jul 12:33
by Safakath Karuthedath,
Yuliar Firdaus,
Ru‐Ze Liang,
Julien Gorenflot,
Pierre M. Beaujuge,
Thomas D. Anthopoulos,
Frédéric Laquai
Energy and charge transfer in ternary organic solar cells (OSC) are investigated by transient spectroscopy. Depending on the excitation wavelength, either exclusive charge transfer or a competition between energy and charge transfer is observed. The presence of PC71BM in the ternary OSC increases the absorption in the UV spectral region and indirectly enhances the electron mobility of ICC6 in the blend.
Abstract
Ternary organic solar cells (OSCs) are among the best‐performing organic photovoltaic devices to date, largely due to the recent development of nonfullerene acceptors. However, fullerene molecules still play an important role in ternary OSC systems, since, for reasons not well understood, they often improve the device performance, despite their lack of absorption. Here, the photophysics of a prototypical ternary small‐molecule OSC blend composed of the donor DR3, the nonfullerene acceptor ICC6, and the fullerene derivative PC71BM is studied by ultrafast spectroscopy. Surprisingly, it is found that after excitation of PC71BM, ultrafast singlet energy transfer to ICC6 competes efficiently with charge transfer. Subsequently, singlets on ICC6 undergo hole transfer to DR3, resulting in free charge generation. Interestingly, PC71BM improves indirectly the electron mobility of the ternary blend, while electrons reside predominantly in ICC6 domains as indicated by fast spectroscopy. The improved mobility facilitates charge carrier extraction, in turn leading to higher device efficiencies of the ternary compared to binary solar cells. Using the (photo)physical parameters obtained from (transient) spectroscopy and charge transport measurements, the device's current–voltage characteristics are simulated and it is demonstrated that the parameters accurately reproduce the experimentally measured device performance.
23 Jul 12:32
by Kun Li,
Yishi Wu,
Yabing Tang,
Ming‐Ao Pan,
Wei Ma,
Hongbing Fu,
Chuanlang Zhan,
Jiannian Yao
A ternary material system–enabled 16.5% efficiency fullerene‐free organic photovoltaic cell is designed with a structurally similar higher‐LUMO‐level guest nonfullerene acceptor. The homogeneous fine morphology and the π–π stacking pattern enable the two acceptors to synergize, obtaining increased open‐circuit voltage, short‐circuit current, and fill factor.
Abstract
Ternary approaches to solar cell design utilizing a small bandgap nonfullerene acceptor as the near infrared absorber to increase the short‐circuit current density always decreases the open‐circuit voltage. Herein, a highly efficient polymer solar cell with an impressive efficiency of 16.28 ± 0.20% enabled by an effective voltage‐increased ternary blended fullerene‐free material approach is reported. In this approach, the structural similarity between the host and the higher‐LUMO‐level guest enables the two acceptors to be synergized, obtaining increased open‐circuit voltage and fill factor and a small increase of short‐circuit current density. The same beneficial effects are demonstrated by using two host binary systems. The homogeneous fine film morphologies and the π–π stacking patterns of the host blend are well maintained, while larger donor and acceptor phases and increased lamellar crystallinity, increased charge mobilities, and reduced monomolecular recombination can be achieved upon addition of the guest nonfullerene acceptor. The increased charge mobilities and reduced monomolecular recombination not only contribute to the improved fill factor but also enable the best devices to be fabricated with a relatively thicker ternary blended active layer (110 vs 100 nm). This, combined with the absorption from the added guest acceptor, contribute to the increased short‐circuit current.
23 Jul 02:47
by Leonardo Evaristo de Sousa†, Fernando Teixeira Bueno‡, Luciano Ribeiro†, Luiz Anto^nio Ribeiro Junior‡§, Deme´trio Anto^nio da Silva Filho*‡§, and Pedro Henrique de Oliveira Neto‡
Chemistry of Materials
DOI: 10.1021/acs.chemmater.9b01281
21 Jul 15:09
by Haohao Feng,
Xin Song,
Zhuohan Zhang,
Renyong Geng,
Jiangsheng Yu,
Linqiang Yang,
Derya Baran,
Weihua Tang
A meta‐alkoxylphenylated dithieno[3,2‐b:2′,3′‐d]pyrrol‐fused nonfullerene acceptor, featuring predominant face‐on orientation in films, enables high‐efficiency as‐cast thick organic solar cells (OSCs). Binary blends with PBDB‐T contributes to a 12.1% power conversion efficiency. Addition of 15 wt% PC71BM renders an efficiency of 14%, among the records for as‐cast single‐junction OSCs. All devices exhibit thickness insensitivity in an active layer thickness window of 82–202 nm.
Abstract
Molecular orientation and π–π stacking of nonfullerene acceptors (NFAs) determine its domain size and purity in bulk‐heterojunction blends with a polymer donor. Two novel NFAs featuring an indacenobis(dithieno[3,2‐b:2ʹ,3ʹ‐d]pyrrol) core with meta‐ or para‐alkoxyphenyl sidechains are designed and denoted as
m‐INPOIC or
p‐INPOIC, respectively. The impact of the alkoxyl group positioning on molecular orientation and photovoltaic performance of NFAs is revealed through a comparison study with the counterpart (INPIC‐4F) bearing para‐alkylphenyl sidechains. With inward constriction toward the conjugated backbone,
m‐INPOIC presents predominant face‐on orientation to promote charge transport. The as‐cast organic solar cells (OSCs) by blending
m‐INPOIC and PBDB‐T as active layers exhibit a power conversion efficiency (PCE) of 12.1%. By introducing PC71BM as the solid processing‐aid, the ternary OSCs are further optimized to deliver an impressive PCE of 14.0%, which is among the highest PCEs for as‐cast single‐junction OSCs reported in literature to date. More attractively, PBDB‐T:
m‐INPOIC:PC71BM based OSCs exhibit over 11% PCEs even with an active layer thickness over 300 nm. And the devices can retain over 95% of PCE after storage for 20 days. The outstanding tolerance to film thickness and outstanding stability of the as‐cast devices make
m‐INPOIC a promising candidate NFA for large‐scale solution‐processable OSCs.
21 Jul 15:08
by Ahmed Ali Said,
Jian Xie,
Yang Wang,
Zongrui Wang,
Yu Zhou,
Kexiang Zhao,
Wei‐Bo Gao,
Tsuyoshi Michinobu,
Qichun Zhang
The sp2‐nitrogen positions in the n‐type (D–A1–D–A2) conjugated polymers have a significant impact on the photovoltaic properties of p–i–n perovskite solar cells when they are used as an electron transporting layer. pBTTz with the HOMO and LUMO levels well‐matched with the valence and conduction bands of the perovskite layer, respectively, shows excellent power conversion efficiency and high stability.
Abstract
It is highly desirable to employ n‐type polymers as electron transporting layers (ETLs) in inverted perovskite solar cells (PSCs) due to their good electron mobility, high hydrophobicity, and simplicity of film forming. In this research, the capability of three n‐type donor–acceptor1–donor–acceptor2 (D–A1–D–A2) conjugated polymers (pBTT, pBTTz, and pSNT) is first explored as ETLs because these polymers possess electron mobilities as high as 0.92, 0.46, and 4.87 cm2 (Vs)−1 in n‐channel organic transistors, respectively. The main structural difference among pBTT, pBTTz, and pSNT is the position of sp2‐nitrogen atoms (sp2‐N) in the polymer main chains. Therefore, the effect of different substitution positions on the PSC performances is comprehensively studied. The as‐fabricated p–i–n PSCs with pBTT, pBTTz, and pSNT as ETLs show the maximum photoconversion efficiencies of 12.8%, 14.4%, and 12.0%, respectively. To be highlighted, pBTTz‐based device can maintain 80% of its stability after ten days due to its good hydrophobicity, which is further confirmed by a contact angle technique. More importantly, the pBTTz‐based device shows a neglected hysteresis. This study reveals that the n‐type polymers can be promising candidates as ETLs to approach solution‐processed highly‐efficient inverted PSCs.
20 Jul 06:16
by Guo-Zhu Zhu, Ling Fung Cheung, Yuan Liu, Chen-Hui Qian, and Lai-Sheng Wang*
The Journal of Physical Chemistry Letters
DOI: 10.1021/acs.jpclett.9b01743
19 Jul 01:09
by Shimin Hu†?, Jiajie Zeng†?, Xiangyu Zhu†, Jingjing Guo†, Shuming Chen‡, Zujin Zhao*†, and Ben Zhong Tang†§
ACS Applied Materials & Interfaces
DOI: 10.1021/acsami.9b06995
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19 Jul 01:09
by Daokun Zhong†, Yue Yu†§, Dongdong Song†, Xiaolong Yang†, Yindi Zhang†, Xi Chen†, Guijiang Zhou*†, and Zhaoxin Wu*‡
ACS Applied Materials & Interfaces
DOI: 10.1021/acsami.9b05950
19 Jul 01:08
by Patrycja Stachelek*†, Jonathan S. Ward‡, Paloma L. dos Santos†, Andrew Danos†, Marco Colella†, Nils Haase§?, Samuel J. Raynes‡, Andrei S. Batsanov‡, Martin R. Bryce*‡, and Andrew P. Monkman*†
ACS Applied Materials & Interfaces
DOI: 10.1021/acsami.9b06364
18 Jul 11:06
by Yahui Liu,
Miao Li,
Jinjin Yang,
Wenyue Xue,
Shiyu Feng,
Jinsheng Song,
Zheng Tang,
Wei Ma,
Zhishan Bo
Steric hindrance of side chains is purposely introduced in the design of planar nonfullerene acceptors. Compared with IDTT2F bearing bare thiophene bridge unit, IDTCN‐C, IDTCN‐O, and IDTCN‐S with alkyl, alkoxyl, and alkylthio substituted thiophene bridge units, all display favorable face‐on orientation and strong crystallinity. An excellent power conversion efficiency of 13.28% based on PBDB‐T:IDTCN‐O is achieved without any additives or annealing treatments.
Abstract
A series of alkyl, alkoxyl, and alkylthio substituted A–π–D–π–A type nonfullerene acceptors (NFAs) IDTCN‐C, IDTCN‐O, and IDTCN‐S are designed and synthesized. The introduction of a lateral side chain at the outer position of the π bridge unit can endow the terminal moiety with a confined planar conformation due to the steric hindrance. Thus, compared with nonsubstituted NFA (IDTT2F), these acceptors tend to form favorable face‐on orientation and exhibit strong crystallinity as verified with grazing‐incidence wide‐angle X‐ray scattering measurement. Moreover, the variation of side chain can significantly change the lowest unoccupied molecular orbital (LUMO) energy level of acceptors. As state‐of‐the‐art NFAs, a power conversion efficiency of 13.28% (V
oc = 0.91 V, J
sc = 19.96 mA cm−2, and FF = 73.2%) is obtained for the as‐cast devices based on IDTCN‐O, which is among the highest value reported in literature. The excellent photovoltaic performance for IDTCN‐O can be attributed to its slightly up‐shifted LUMO level and more balanced charge transport. This research demonstrates side chain engineering is an effective way to achieve high efficiency organic solar cells.
16 Jul 13:07
by Weixuan Zeng,
Tao Zhou,
Weimin Ning,
Cheng Zhong,
Jiawei He,
Shaolong Gong,
Guohua Xie,
Chuluo Yang
Solution‐processed red fluorescent organic light‐emitting diodes (OLEDs) with external quantum efficiencies of up to 22.5% are fabricated using a synergistic strategy of molecular engineering and host selection with thermally activated delayed‐fluorescence emitters. With this strategy, a good balance of the critical photophysical parameters is realized by effectively fine tuning the excited states of the emitters, which is verified to support the record‐high efficiency reported.
Abstract
Developing high‐efficiency solution‐processable thermally activated delayed‐fluorescence (TADF) emitters, especially in longer wavelength regions, is a formidable challenge. Three red TADF emitters, namely NAI_R1, NAI_R2, and NAI_R3, are developed by phenyl encapsulation and tert‐butyl substitution on a prototypical 1,8‐naphthalimide‐acridine hybrid. This design strategy not only grants these molecules high solubility, excellent thermal stability, and good film‐forming ability, but also pulls down their charge‐transfer (CT) energy levels excited states. Furthermore, dispersing these emitters into two different host materials of mCP and mCPCN finely tailors their CT‐state energy levels. More importantly, a synergistic combination of molecular engineering and host selection can effectively manipulate the competition between the radiative and nonradiative decay rates of the CT singlet states of these emitters and the reverse intersystem crossing from their triplet to singlet states. Consequently, the optimal combination of NAI_R3 emitter and mCP host successfully results in a state‐of‐the‐art external quantum efficiency (EQE) of 22.5% for solution‐processed red TADF organic light‐emitting diodes (OLEDs) with an emission peak above 620 nm. This finding demonstrates that a synergistic strategy of molecular engineering and host selection with TADF emitters could provide a new pathway for developing efficient solution‐processable TADF systems.
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