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24 Mar 16:29

Relating Frontier Orbital Energies from Voltammetry and Photoelectron Spectroscopy to the Open‐Circuit Voltage of Organic Solar Cells

by Robin E. M. Willems, Christ H. L. Weijtens, Xander Vries, Reinder Coehoorn, René A. J. Janssen
Advanced Energy Materials Relating Frontier Orbital Energies from Voltammetry and Photoelectron Spectroscopy to the Open‐Circuit Voltage of Organic Solar Cells

To predict the open‐circuit voltage (V oc) of polymer–fullerene solar cells, three independent methods, square‐wave voltammetry (SWV), ultraviolet photoelectron spectroscopy, and density functional theory, are compared. For 19 diketopyrrolopyrrole polymers, SWV gives the best correlation. Remarkably, the slope of V oc with the blend's electrochemical gap is less than unity and possible reasons for this result are discussed.


Abstract

For 19 diketopyrrolopyrrole polymers, the highest occupied molecular orbital (HOMO) energies are determined from i) the oxidation potential with square‐wave voltammetry (SWV), ii) the ionization potential using ultraviolet photoelectron spectroscopy (UPS), and iii) density functional theory (DFT) calculations. The SWV HOMO energies show an excellent linear correlation with the open‐circuit voltage (V oc) of optimized solar cells in which the polymers form blends with a fullerene acceptor ([6,6]‐phenyl‐C61‐butyl acid methyl ester or [6,6]‐phenyl‐C71‐butyl acid methyl ester). Remarkably, the slope of the best linear fit is 0.75 ± 0.04, i.e., significantly less than unity. A weaker correlation with V oc is found for the HOMO energies obtained from UPS and DFT. Within the experimental error, the SWV and UPS data are correlated with a slope close to unity. The results show that electrochemically determined oxidation potentials provide an excellent method for predicting the V oc of bulk heterojunction solar cells, with absolute deviations less than 0.1 V.

24 Mar 16:28

Reduced Energy Loss Enabled by a Chlorinated Thiophene‐Fused Ending‐Group Small Molecular Acceptor for Efficient Nonfullerene Organic Solar Cells with 13.6% Efficiency

by Zhenghui Luo, Tao Liu, Yiling Wang, Guangye Zhang, Rui Sun, Zhangxiang Chen, Cheng Zhong, Jingnan Wu, Yuzhong Chen, Maojie Zhang, Yang Zou, Wei Ma, He Yan, Jie Min, Yongfang Li, Chuluo Yang
Advanced Energy Materials Reduced Energy Loss Enabled by a Chlorinated Thiophene‐Fused Ending‐Group Small Molecular Acceptor for Efficient Nonfullerene Organic Solar Cells with 13.6% Efficiency

The ITC‐2Cl‐based device yields an excellent power conversion efficiency of 13.6% with a low E loss of 0.67 eV, which is superior to those of the devices based on ITCPTC, IT‐4F, and IT‐4Cl.


Abstract

Generally, highly efficient organic solar cells require both a high open‐circuit voltage (V OC) and a high short‐circuit current density (J SC). Reducing the energy loss (E loss) is an effective way to achieve a high V OC without compromising the photocurrent, which is ideal for enhancing the power conversion efficiencies (PCEs). Herein, a new chlorinated nonfullerene acceptor (ITC‐2Cl) with chlorinated thiophene‐fused end groups is developed. In comparison with the unchlorinated counterpart (ITCPTC), the introduction of Cl improves not only the electronic properties by redshifting the absorption spectra and deepening the lowest unoccupied molecular orbital energy levels, but also the molecular packing and thus thin‐film morphology. The PM6:ITC‐2Cl‐based device yields a significantly higher PCE (13.6%) with a lower E loss (0.67 eV) than the ITCPTC‐based device (PCE of 12.3% with E loss of 0.70 eV). More importantly, compared to the archetypal nonfullerene acceptors such as IT‐4F (PCE of 12.9% with E loss of 0.73 eV) and IT‐4Cl (PCE of 12.7% with E loss of 0.76 eV), the ITC‐2Cl‐based device shows a higher PCE and a lower E loss. These results demonstrate that the chlorinated thiophene‐fused end group is a promising candidate for a high‐performance nonfullerene acceptors with low energy loss.

24 Mar 16:27

15% Efficiency Tandem Organic Solar Cell Based on a Novel Highly Efficient Wide‐Bandgap Nonfullerene Acceptor with Low Energy Loss

by Gongchu Liu, Jianchao Jia, Kai Zhang, Xiao'e Jia, Qingwu Yin, Wenkai Zhong, Li Li, Fei Huang, Yong Cao
Advanced Energy Materials 15% Efficiency Tandem Organic Solar Cell Based on a Novel Highly Efficient Wide‐Bandgap Nonfullerene Acceptor with Low Energy Loss

A novel wide‐bandgap nonfullerene acceptor TfIF‐4FIC is synthesized. PBDB‐T‐2F:TfIF‐4FIC‐based organic solar cell acquires a power conversion efficiency (PCE) of 13.1%, a high open‐circuit voltage of 0.98 V, which is the best performed device with bandgap larger than 1.60 eV. When using PBDB‐T‐2F:TfIF‐4FIC as front cell and PTB7‐Th:PCDTBT:IEICO‐4F as back cell to construct tandem device, PCE of 15% is achieved.


Abstract

A tandem organic solar cell (OSC) is a valid structure to widen the photon response range and suppress the transmission loss and thermalization loss. In the past few years, the development of low‐bandgap materials with broad absorption in long‐wavelength region for back subcells has attracted considerable attention. However, wide‐bandgap materials for front cells that have both high short‐circuit current density (J SC) and open‐circuit voltage (V OC) are scarce. In this work, a new fluorine‐substituted wide‐bandgap small molecule nonfullerene acceptor TfIF‐4FIC is reported, which has an optical bandgap of 1.61 eV. When PBDB‐T‐2F is selected as the donor, the device offers an extremely high V OC of 0.98 V, a high J SC of 17.6 mA cm−2, and a power conversion efficiency of 13.1%. This is the best performing acceptor with such a wide bandgap. More importantly, the energy loss in this combination is 0.63 eV. These properties ensure that PBDB‐T‐2F:TfIF‐4FIC is an ideal candidate for the fabrication of tandem OSCs. When PBDB‐T‐2F:TfIF‐4FIC and PTB7‐Th:PCDTBT:IEICO‐4F are used as the front cell and the back cell to construct tandem solar cells, a PCE of 15% is obtained, which is one of best results reported to date in the field of organic solar cells.

24 Mar 16:26

High‐Performance Perovskite Solar Cells with Excellent Humidity and Thermo‐Stability via Fluorinated Perylenediimide

by Jia Yang, Cong Liu, Chunsheng Cai, Xiaotian Hu, Zengqi Huang, Xiaopeng Duan, Xiangchuan Meng, Zhongyi Yuan, Licheng Tan, Yiwang Chen
Advanced Energy Materials High‐Performance Perovskite Solar Cells with Excellent Humidity and Thermo‐Stability via Fluorinated Perylenediimide

Fluorinated perylenediimide (F‐PDI) is first introduced to optimize photovoltaic performance and stability of perovskite solar cells. Conductive F‐PDI effectively passivates defects and promotes charge transfer. The hydrophobicity of F‐PDI preventing moisture penetration as well as the strong hydrogen bonding immobilizing methylamine ions, thereby, endow excellent moisture and thermal stability with nearly 70% efficiency retention after thermal treatment at 100 °C.


Abstract

The notoriously poor stability of perovskite solar cells is a crucial issue restricting commercial applications. Here, a fluorinated perylenediimide (F‐PDI) is first introduced into perovskite film to enhance the device's photovoltaic performance, as well as thermal and moisture stability simultaneously. The conductive F‐PDI molecules filling at grain boundaries (GBs) and surface of perovskite film can passivate defects and promote charge transport through GBs due to the chelation between carbonyl of F‐PDI and noncoordinating lead. Furthermore, an effective multiple hydrophobic structure is formed to protect perovskite film from moisture erosion. As a result, the F‐PDI‐incorporated devices based on MAPbI3 and Cs0.05 (FA0.83MA0.17)0.95 Pb (Br0.17I0.83)3 absorber achieve champion efficiencies of 18.28% and 19.26%, respectively. Over 80% of the initial efficiency is maintained after exposure in air for 30 days with a relative humidity (RH) of 50%. In addition, the strong hydrogen bonding of F···H‐N can immobilize methylamine ion (MA+) and thus enhances the thermal stability of device, remaining nearly 70% of the initial value after thermal treatment (100 °C) for 24 h at 50% RH condition.

24 Mar 14:23

[ASAP] Semiconducting Properties and Geometry-Directed Self-Assembly of Heptacyclic Anthradithiophene Diimide-Based Polymers

by Jianyao Huang, Zhihui Chen, Jie Yang, Huanxin Ju, Weifeng Zhang, Gui Yu

TOC Graphic

Chemistry of Materials
DOI: 10.1021/acs.chemmater.8b05353
24 Mar 14:22

[ASAP] Chiral Bidentate Boryl Ligand Enabled Iridium-Catalyzed Asymmetric C(sp2)–H Borylation of Diarylmethylamines

by Xiaoliang Zou, Haonan Zhao, Yinwu Li, Qian Gao, Zhuofeng Ke, Senmiao Xu

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Journal of the American Chemical Society
DOI: 10.1021/jacs.8b13756
19 Mar 09:22

[ASAP] Polymer Side-Chain Variation Induces Microstructural Disparity in Nonfullerene Solar Cells

by Long Ye, Wanbin Li, Xia Guo, Maojie Zhang, Harald Ade

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Chemistry of Materials
DOI: 10.1021/acs.chemmater.9b00174
19 Mar 09:22

[ASAP] Multiarm and Substituent Effects on Charge Transport of Organic Hole Transport Materials

by Kun-Han Lin, Antonio Prlj, Liang Yao, Nikita Drigo, Han-Hee Cho, Mohammad Khaja Nazeeruddin, Kevin Sivula, Clémence Corminboeuf

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Chemistry of Materials
DOI: 10.1021/acs.chemmater.9b00438
19 Mar 09:21

[ASAP] Fused Heptacyclic-Based Acceptor–Donor–Acceptor Small Molecules: N-Substitution toward High-Performance Solution-Processable Field-Effect Transistors

by Guobing Zhang, Yao Zhao, Boseok Kang, Sangsik Park, Jiufu Ruan, Hongbo Lu, Longzhen Qiu, Yunsheng Ding, Kilwon Cho

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Chemistry of Materials
DOI: 10.1021/acs.chemmater.8b05054
14 Mar 16:03

[ASAP] Organic Semiconducting Alloys with Tunable Energy Levels

by Jin-Hu Dou, Zhi-Ao Yu, Jun Zhang, Yu-Qing Zheng, Ze-Fan Yao, Zeyi Tu, Xinchang Wang, Shiliang Huang, Chengwen Liu, Junliang Sun, Yuanping Yi, Xiaoyu Cao, Yiqin Gao, Jie-Yu Wang, Jian Pei

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Journal of the American Chemical Society
DOI: 10.1021/jacs.8b13471
14 Mar 16:02

[ASAP] Analytical Platform To Characterize Dopant Solution Concentrations, Charge Carrier Densities in Films and Interfaces, and Physical Diffusion in Polymers Utilizing Remote Field-Effect Transistors

by Hyun-June Jang, Justine Wagner, Hui Li, Qingyang Zhang, Tushita Mukhopadhyaya, Howard E. Katz

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Journal of the American Chemical Society
DOI: 10.1021/jacs.8b13026
12 Mar 02:17

Regulating Bulk‐Heterojunction Molecular Orientations through Surface Free Energy Control of Hole‐Transporting Layers for High‐Performance Organic Solar Cells

by Jianqiu Wang, Zhong Zheng, Dongyang Zhang, Jianqi Zhang, Jiyu Zhou, Jingchong Liu, Shenkun Xie, Yong Zhao, Yuan Zhang, Zhixiang Wei, Jianhui Hou, Zhiyong Tang, Huiqiong Zhou
Advanced Materials Regulating Bulk‐Heterojunction Molecular Orientations through Surface Free Energy Control of Hole‐Transporting Layers for High‐Performance Organic Solar Cells

The molecular orientation and charge extraction of PEDOT:PSS‐based hole‐transporting layers are effectively modulated through fine tuning of the surface energy by introducing poly(styrene sulfonic acid) sodium salts or nickel formate dihydrate, which boosts the fill factor and eventual efficiency of organic solar cells based on fullerene and nonfullerene acceptors.


Abstract

Interface properties are of critical importance for high‐performance bulk‐heterojunction (BHJ) organic solar cells (OSCs). Here, a universal interface approach to tune the surface free energy (γS) of hole‐transporting layers (HTLs) in a wide range through introducing poly(styrene sulfonic acid) sodium salts or nickel formate dihydrate into poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is reported. Based on the optimal γS of HTLs and thus improved face‐on molecular ordering in BHJs, enhanced fill factor and power conversion efficiencies in both fullerene and nonfullerene OSCs are achieved, which is attributed to the increased charge carrier mobility and sweepout with reduced recombination. It is found that the face‐on orientation‐preferred BHJs (PBDB‐TF:PC71BM, PBDB‐T:PC71BM, and PBDB‐TF:IT‐4F) favor HTLs with higher γS while the edge‐on orientation‐preferred BHJs (PDCDT:PC71BM, P3HT:PC71BM and PDCBT:ITIC) are partial to HTLs with lower γS. Based on the surface property–morphology–device performance correlations, a suggestion to select a suitable HTL in terms of γS for a specific BHJ with favored molecular arrangement is provided. This work enriches the fundamental understandings on the interface characteristics and morphological control toward high‐efficiency OSCs based on a wide range of BHJ materials.

10 Mar 15:13

Control of Molecular Orientation in Organic Semiconductor Films using Weak Hydrogen Bonds

by Yuichiro Watanabe, Daisuke Yokoyama, Tomoyuki Koganezawa, Hiroshi Katagiri, Takashi Ito, Satoru Ohisa, Takayuki Chiba, Hisahiro Sasabe, Junji Kido
Advanced Materials Control of Molecular Orientation in Organic Semiconductor Films using Weak Hydrogen Bonds

Self‐complementary weak hydrogen bonds of oligopyridines can be used to control molecular orientation for designing horizontally oriented yet amorphous organic semiconductor films. Synergetic effects of disordered hydrogen bonds and planar anisotropic molecular shapes enhance horizontal molecular orientation and significantly increasing electron mobility. This molecular engineering methodology delivers a highly efficient and stable organic optoelectronic device as a proof‐of‐concept.


Abstract

Use of the intrinsic optoelectronic functions of organic semiconductor films has not yet reached its full potential, mainly because of the primitive methodology used to control the molecular aggregation state in amorphous films during vapor deposition. Here, a universal molecular engineering methodology is presented to control molecular orientation; this methodology strategically uses noncovalent, intermolecular weak hydrogen bonds in a series of oligopyridine derivatives. A key is to use two bipyridin‐3‐ylphenyl moieties, which form self‐complementary intermolecular weak hydrogen bonds, and which do not induce unfavorable crystallization. Another key is to incorporate a planar anisotropic molecular shape by reducing the steric hindrance of the core structure for inducing π–π interactions. These synergetic effects enhance horizontal orientation in amorphous organic semiconductor films and significantly increasing electron mobility. Through this evaluation process, an oligopyridine derivative is selected as an electron‐transporter, and successfully develops highly efficient and stable deep‐red organic light‐emitting devices as a proof‐of‐concept.

10 Mar 15:09

[ASAP] Spectroscopic Investigation of the Effect of Microstructure and Energetic Offset on the Nature of Interfacial Charge Transfer States in Polymer: Fullerene Blends

by S. D. Dimitrov, M. Azzouzi, J. Wu, J. Yao, Y. Dong, P. Shakya Tuladhar, B. C. Schroeder, E. R. Bittner, I. McCulloch, J. Nelson, J. R. Durrant

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Journal of the American Chemical Society
DOI: 10.1021/jacs.8b11484
06 Mar 06:01

A Novel Hybrid‐Layered Organic Phototransistor Enables Efficient Intermolecular Charge Transfer and Carrier Transport for Ultrasensitive Photodetection

by Yuanhong Gao, Ya Yi, Xinwei Wang, Hong Meng, Dangyuan Lei, Xue‐Feng Yu, Paul K. Chu, Jia Li
Advanced Materials A Novel Hybrid‐Layered Organic Phototransistor Enables Efficient Intermolecular Charge Transfer and Carrier Transport for Ultrasensitive Photodetection

A novel hybrid‐layered organic phototransistor, (HL‐OPT) architecture consisting of an organic semiconductor channel layer for fast carrier transport, a photoactive organic bulk‐heterojunction layer, and an ultrathin inorganic interlayer sandwiched in between is proposed. By combining the virtues of the charge‐trapping effect and efficient carrier transport simultaneously, significant enhancement in the photodetection performance is achieved from the fabricated HL‐OPT.


Abstract

The interfacial charge effect is crucial for high‐sensitivity organic phototransistors (OPTs), but conventional layered and hybrid OPTs have a trade‐off in balancing the separation, transport, and recombination of photogenerated charges, consequently impacting the device performance. Herein, a novel hybrid‐layered phototransistor (HL‐OPT) is reported with significantly improved photodetection performance, which takes advantages of both the charge‐trapping effect (CTE) and efficient carrier transport. The HL‐OPT consisting of 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene (C8‐BTBT) as conduction channel, C8‐BTBT:[6,6]‐phenyl‐C61‐butyric acid methyl ester (PC61BM) bulk heterojunction as photoactive layer, and sandwiched MoO3 interlayer as a charge‐transport interlayer exhibits outstanding photodetection characteristics such as a photosensitivity (I light/I dark) of 2.9 × 106, photoresponsivity (R) of 8.6 × 103 A W−1, detectivity (D*) of 3.4 × 1014 Jones, and external quantum efficiency of 3 × 106% under weak light illumination of 32 µW cm−2. The mechanism and strategy described here provide new insights into the design and optimization of high‐performance OPTs spanning the ultraviolet and near infrared (NIR) range as well as fundamental issues pertaining to the electronic and photonic properties of the devices.

06 Mar 06:00

[ASAP] Phytol-Derived Alkyl Side Chains for p-Conjugated Semiconducting Polymers

by Fanji Wang, Kyohei Nakano, Hiroshi Segawa, Keisuke Tajima

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Chemistry of Materials
DOI: 10.1021/acs.chemmater.8b05240
02 Mar 18:00

Twist and Degrade—Impact of Molecular Structure on the Photostability of Nonfullerene Acceptors and Their Photovoltaic Blends

by Joel Luke, Emily M. Speller, Andrew Wadsworth, Mark F. Wyatt, Stoichko Dimitrov, Harrison K. H. Lee, Zhe Li, Wing C. Tsoi, Iain McCulloch, Diego Bagnis, James R. Durrant, Ji‐Seon Kim
Advanced Energy Materials Twist and Degrade—Impact of Molecular Structure on the Photostability of Nonfullerene Acceptors and Their Photovoltaic Blends

Nonfullerene acceptors (NFAs) provide an exciting prospect for organic solar cells; however, their stability still lacks fundamental understanding. The promising high‐efficiency NFAs, IDTBR and IDFBR, show a three‐phase degradation mechanism, which involves a strong initial molecular conformational change prior to photodegradation under light and oxygen stress, indicating the important role of NFA molecular structure in solar cell stability.


Abstract

Nonfullerene acceptors (NFAs) dominate organic photovoltaic (OPV) research due to their promising efficiencies and stabilities. However, there is very little investigation into the molecular processes of degradation, which is critical to guiding design of novel NFAs for long‐lived, commercially viable OPVs. Here, the important role of molecular structure and conformation in NFA photostability in air is investigated by comparing structurally similar but conformationally different promising NFAs: planar O‐IDTBR and nonplanar O‐IDFBR. A three‐phase degradation process is identified: i) initial photoinduced conformational change (i.e., torsion about the core–benzothiadiazole dihedral), induced by noncovalent interactions with environmental molecules, ii) followed by photo‐oxidation and fragmentation, leading to chromophore bleaching and degradation product formation, and iii) finally complete chromophore bleaching. Initial conformational change is a critical prerequisite for further degradation, providing fundamental understanding of the relative stability of IDTBR and IDFBR, where the already twisted IDFBR is more prone to degradation. When blended with the donor polymer poly(3‐hexylthiophene), both NFAs exhibit improved photostability while the photostability of the polymer itself is significantly reduced by the more miscible twisted NFA. The findings elucidate the important role of NFA molecular structure in photostability of OPV systems, and provide vital insights into molecular design rules for intrinsically photostable NFAs.

02 Mar 18:00

Significant Effect of Fluorination on Simultaneously Improving Work Function and Transparency of Anode Interlayer for Organic Solar Cells

by Lili Lu, Qing Liao, Yunfei Zu, Ye Xu, Bowei Xu, Jianhui Hou
Advanced Energy Materials Significant Effect of Fluorination on Simultaneously Improving Work Function and Transparency of Anode Interlayer for Organic Solar Cells

Through the rational molecular design of fluorination, the work function of the conjugated polymer (CP) is enhanced from 4.83 to 5.00 eV. Consequently, the CP can be used to modify efficient active layers consisting of polymer donors with a deep HOMO level, such as PBDB‐T‐2F:IT‐4F, and an outstanding power conversion efficiency of 12.7% is achieved in the corresponding device without V oc loss.


Abstract

Since the highest occupied molecular orbital (HOMO) level of donors in organic solar cells (OSCs) is being constantly downshifted for achieving high open‐circuit voltage (V oc), a further enhancement of the anode work function (WF) is required. Herein, an effective approach of fluorination is demonstrated to simultaneously improve the WF and transparency for anode interlayer (AIL) material. By fluorination, in combination with the dialysis treatment in LiCl solution, the WF of PCP‐2F‐Li could be significantly enhanced from 4.86 to 5.0 eV, as compared to PCP‐Na. Meanwhile, the transparency of the polymer is also improved. As a result, PCP‐2F‐Li can be used to modify efficient active layers consisting of polymer donors with deep HOMO levels, such as PBDB‐T‐2F:IT‐4F, and an outstanding power conversion efficiency (PCE) of 12.7% is achieved in the corresponding device with a high V oc of 0.84 V. This result represents the highest efficiency for the OSCs using a solution‐processed pH‐neutral AIL, which is beneficial to the low‐cost fabrication of high‐performance OSCs with improved stability. More importantly, PCP‐2F‐Li could be processed by blade coating for making large‐area device of 1 cm2, and a PCE of 10.6% is achieved, bringing a promising prospect for the large‐area device fabrication.

27 Feb 06:22

[ASAP] Chemical Stabilities of the Lowest Triplet State in Aryl Sulfones and Aryl Phosphine Oxides Relevant to OLED Applications

by Huifang Li, Minki Hong, Annabelle Scarpaci, Xuyang He, Chad Risko, John S. Sears, Stephen Barlow, Paul Winget, Seth R. Marder, Dongwook Kim, Jean-Luc Brédas

TOC Graphic

Chemistry of Materials
DOI: 10.1021/acs.chemmater.8b04235
27 Feb 03:35

Achieving Over 15% Efficiency in Organic Photovoltaic Cells via Copolymer Design

by Yong Cui, Huifeng Yao, Ling Hong, Tao Zhang, Ye Xu, Kaihu Xian, Bowei Gao, Jinzhao Qin, Jianqi Zhang, Zhixiang Wei, Jianhui Hou
Advanced Materials Achieving Over 15% Efficiency in Organic Photovoltaic Cells via Copolymer Design

Organic solar cells achieve over 15% efficiency through the use of a copolymer donor, and simultaneously enhanced open‐circuit voltage and short‐circuit current density are obtained. High‐performance solar cells are adaptable for environment‐friendly solvents using a blade‐coating method, while showing better photostability than the corresponding ternary solar cells.


Abstract

Ternary blending and copolymerization strategies have proven advantageous in boosting the photovoltaic performance of organic solar cells. Here, 15% efficiency solar cells using copolymerization donors are demonstrated, where the electron‐withdrawing unit, ester‐substituted thiophene, is incorporated into a PBDB‐TF polymer to downshift the molecular energy and broaden the absorption. Copolymer‐based solar cells suitable for large‐area devices can be fabricated by a blade‐coating method from a nonhalogen and nonaromatic solvent mixture. Although ternary solar cells can achieve comparable efficiencies, they are not suitable for environment‐friendly processing conditions and show relatively low photostability compared to copolymer‐based devices. These results not only demonstrate high‐efficiency organic photovoltaic cells via copolymerization strategies but also provide important insights into their applications in practical production.

27 Feb 03:34

2D–Organic Hybrid Heterostructures for Optoelectronic Applications

by Jia Sun, Yongsuk Choi, Young Jin Choi, Seongchan Kim, Jin‐Hong Park, Sungjoo Lee, Jeong Ho Cho
Advanced Materials 2D–Organic Hybrid Heterostructures for Optoelectronic Applications

The hybridization of 2D materials and organic materials represents a promising domain for the realization of improved or unprecedented features in comparison to those of semiconductor devices. This comprehensive review focuses on emerging 2D–organic heterostructures (from their synthesis and fabrication to their state‐of‐the‐art optoelectronic applications) and highlights the future challenges and opportunities associated with these heterostructures.


Abstract

The unique properties of hybrid heterostructures have motivated the integration of two or more different types of nanomaterials into a single optoelectronic device structure. Despite the promising features of organic semiconductors, such as their acceptable optoelectronic properties, availability of low‐cost processes for their fabrication, and flexibility, further optimization of both material properties and device performances remains to be achieved. With the emergence of atomically thin 2D materials, they have been integrated with conventional organic semiconductors to form multidimensional heterostructures that overcome the present limitations and provide further opportunities in the field of optoelectronics. Herein, a comprehensive review of emerging 2D–organic heterostructures—from their synthesis and fabrication to their state‐of‐the‐art optoelectronic applications—is presented. Future challenges and opportunities associated with these heterostructures are highlighted.

27 Feb 03:33

Surface and Interface Properties in Thin‐Film Solar Cells: Using Soft X‐rays and Electrons to Unravel the Electronic and Chemical Structure

by Lothar Weinhardt, Dirk Hauschild, Clemens Heske
Advanced Materials Surface and Interface Properties in Thin‐Film Solar Cells: Using Soft X‐rays and Electrons to Unravel the Electronic and Chemical Structure

Electron and soft X‐ray spectroscopies are powerful techniques to study the chemical and electronic structure of surfaces and interfaces. In this progress report, these techniques are used to study solar devices and to unravel some of the most pertinent aspects of recent cutting‐edge developments (and world‐record efficiency improvements) in chalcopyrite thin‐film solar cells.


Abstract

Thin‐film solar cells have great potential to overtake the currently dominant silicon‐based solar cell technologies in a strongly growing market. Such thin‐film devices consist of a multilayer structure, for which charge‐carrier transport across interfaces plays a crucial role in minimizing the associated recombination losses and achieving high solar conversion efficiencies. Further development can strongly profit from a high‐level characterization that gives a local, electronic, and chemical picture of the interface properties, which allows for an insight‐driven optimization. Herein, the authors' recent progress of applying a “toolbox” of high‐level laboratory‐ and synchrotron‐based electron and soft X‐ray spectroscopies to characterize the chemical and electronic properties of such applied interfaces is provided. With this toolbox in hand, the activities are paired with those of experts in thin‐film solar cell preparation at the cutting edge of current developments to obtain a deeper understanding of the recent improvements in the field, e.g., by studying the influence of so‐called “post‐deposition treatments”, as well as characterizing the properties of interfaces with alternative buffer layer materials that give superior efficiencies on large, module‐sized areas.

27 Feb 03:31

Recent Advances in n‐Type Polymers for All‐Polymer Solar Cells

by Zewdneh Genene, Wendimagegn Mammo, Ergang Wang, Mats R. Andersson
Advanced Materials Recent Advances in n‐Type Polymers for All‐Polymer Solar Cells

The rapid development of n‐type polymers has boosted the efficiency of all‐polymer solar cells, which has improved from 2% to 10 % in only seven years. There is a strong need to summarize the design criteria, synthesis, structure–property relationships and recent advances of n‐type polymers, which is addressed in this review. Moreover, the challenges and prospects for further development of all‐PSCs are briefly discussed.


Abstract

All‐polymer solar cells (all‐PSCs) based on n‐ and p‐type polymers have emerged as promising alternatives to fullerene‐based solar cells due to their unique advantages such as good chemical and electronic adjustability, and better thermal and photochemical stabilities. Rapid advances have been made in the development of n‐type polymers consisting of various electron acceptor units for all‐PSCs. So far, more than 200 n‐type polymer acceptors have been reported. In the last seven years, the power conversion efficiency (PCE) of all‐PSCs rapidly increased and has now surpassed 10%, meaning they are approaching the performance of state‐of‐the‐art solar cells using fullerene derivatives as acceptors. This review discusses the design criteria, synthesis, and structure–property relationships of n‐type polymers that have been used in all‐PSCs. Additionally, it highlights the recent progress toward photovoltaic performance enhancement of binary, ternary, and tandem all‐PSCs. Finally, the challenges and prospects for further development of all‐PSCs are briefly considered.

25 Feb 13:09

[ASAP] Achieving Balanced Charge Transport and Favorable Blend Morphology in Non-Fullerene Solar Cells via Acceptor End Group Modification

by Minghui Hao, Tao Liu, Yiqun Xiao, Lik-Kuen Ma, Guangye Zhang, Cheng Zhong, Zhanxiang Chen, Zhenghui Luo, Xinhui Lu, He Yan, Lei Wang, Chuluo Yang

TOC Graphic

Chemistry of Materials
DOI: 10.1021/acs.chemmater.8b05327
25 Feb 13:08

[ASAP] New Design Paradigm for Color Control in Anodically Coloring Electrochromic Molecules

by Dylan T. Christiansen, Aimée L. Tomlinson, John R. Reynolds

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Journal of the American Chemical Society
DOI: 10.1021/jacs.9b01507
18 Feb 08:07

[ASAP] Carrier Dynamics and Morphology Regulated by 1,8-Diiodooctane in Chlorinated Nonfullerene Polymer Solar Cells

by Hui Chen, Jianfei Qu, Longzhu Liu, Wei Chen, Feng He

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The Journal of Physical Chemistry Letters
DOI: 10.1021/acs.jpclett.9b00063
18 Feb 08:06

Predicting Operational Stability for Organic Light‐Emitting Diodes with Exciplex Cohosts

by Zhiheng Wang, Mengke Li, Lin Gan, Xinyi Cai, Binbin Li, Dongcheng Chen, Shi‐Jian Su
Advanced Science Predicting Operational Stability for Organic Light‐Emitting Diodes with Exciplex Cohosts

By proposing a lifetime prediction method via coordinating dissociated activation energy description with exciton density as a function of time, exciplex cohost molecular stability and dominated dissociation mechanism are successfully predicted. The strong chemical bond for the hole transport moieties and rapid reactive exciton relaxation provide the managing strategies to access long‐lived exciplex cohosts.


Abstract

Organic light‐emitting diodes (OLEDs) employing exciplex cohosts have gained attractive interest due to the promising high efficiency, low driving voltage, and potential low cost in future solid‐state lighting sources and full‐color displays. However, their device lifetime is still the most challenging weakness and rarely studied, which is regarded as a time consuming and complicated work. Therefore, a simplified but effective and comprehensive approach is demonstrated to give prediction for the exciplex cohosts operating lifespan and analyze their possible degradation mechanisms by considering molecular dissociated activation energy with internal exciton dynamics correlations. As a consequence, strong chemical bond stability for the hole transport moieties and rapid reactive exciton relaxation have the intrinsic talent to access potentially long‐lived exciplex cohosts, achieving an extended lifetime of 10169 h for the predicted long‐lived exciplex cohost OLEDs. Degradation behaviors further confirm that the deteriorated source is attributed to the formation of exciton quenchers and hole traps from excited states and charged‐excited states, respectively. The current findings establish a universal technique to screen the stable exciplex cohost candidates with economic time consumption and expenses.

17 Feb 16:27

Energy-level engineering of the electron transporting layer for improving open-circuit voltage in dye and perovskite-based solar cells

Energy Environ. Sci., 2019, 12,958-964
DOI: 10.1039/C8EE03672A, Communication
Seong Sik Shin, Jae Ho Suk, Bong Joo Kang, Wenping Yin, Seon Joo Lee, Jun Hong Noh, Tae Kyu Ahn, Fabian Rotermund, In Sun Cho, Sang Il Seok
BaSnO3 is designed as an electron transport layer of high-efficiency perovskite and dye-sensitized solar cells by fine-tuning energy levels through substitution of specific amounts of Sr ions.
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17 Feb 16:26

Recent Progress of Singlet‐Exciton‐Harvesting Fluorescent Organic Light‐Emitting Diodes by Energy Transfer Processes

by Sung Yong Byeon, Dong Ryun Lee, Kyoung Soo Yook, Jun Yeob Lee
Advanced Materials Recent Progress of Singlet‐Exciton‐Harvesting Fluorescent Organic Light‐Emitting Diodes by Energy Transfer Processes

Recent progress regarding thermally activated delayed fluorescence (TADF) sensitized fluorescent organic light‐emitting diodes (OLEDs) is discussed, based on both external quantum efficiency, reported by material, and device engineering.


Abstract

The external quantum efficiency (EQE) of organic light‐emitting diodes (OLEDs) has been dramatically improved by developing highly efficient organic emitters such as phosphorescent emitters and thermally activated delayed fluorescent (TADF) emitters. However, high‐EQE OLED technologies suffer from relatively poor device lifetimes in spite of their high EQEs. In particular, the short lifetimes of blue phosphorescent and TADF OLEDs remain a big hurdle to overcome. Therefore, the high‐EQE approach harvesting singlet excitons of fluorescent emitters by energy transfer processes from the host or sensitizer has been explored as an alternative for high‐EQE OLED strategies. Recently, there has been a big jump in the EQE and device lifetime of singlet‐exciton‐harvesting fluorescent OLEDs. Recent progress on the materials and device structure is discussed herein.

17 Feb 16:25

High‐Performance All‐Polymer Solar Cells Enabled by an n‐Type Polymer Based on a Fluorinated Imide‐Functionalized Arene

by Huiliang Sun, Yumin Tang, Chang Woo Koh, Shaohua Ling, Ruizhi Wang, Kun Yang, Jianwei Yu, Yongqiang Shi, Yingfeng Wang, Han Young Woo, Xugang Guo
Advanced Materials High‐Performance All‐Polymer Solar Cells Enabled by an n‐Type Polymer Based on a Fluorinated Imide‐Functionalized Arene

Ring fusion and backbone fluorination yield a novel ladder‐type building block f‐FBTI2, a desirable “stronger acceptor” for enabling n‐type electron‐acceptor polymers. The resulting polymer semiconductor f‐FBTI2‐T shows an excellent power conversion efficiency of 8.1% with a very small energy loss of 0.53 eV in all‐polymer solar cell devices.


Abstract

A novel imide‐functionalized arene, di(fluorothienyl)thienothiophene diimide (f‐FBTI2), featuring a fused backbone functionalized with electron‐withdrawing F atoms, is designed, and the synthetic challenges associated with highly electron‐deficient fluorinated imide are overcome. The incorporation of f‐FBTI2 into polymer affords a high‐performance n‐type semiconductor f‐FBTI2‐T, which shows a reduced bandgap and lower‐lying lowest unoccupied molecular orbital (LUMO) energy level than the polymer analog without F or with F‐functionalization on the donor moiety. These optoelectronic properties reflect the distinctive advantages of fluorination of electron‐deficient acceptors, yielding “stronger acceptors,” which are desirable for n‐type polymers. When used as a polymer acceptor in all‐polymer solar cells, an excellent power conversion efficiency of 8.1% is achieved without any solvent additive or thermal treatment, which is the highest value reported for all‐polymer solar cells except well‐studied naphthalene diimide and perylene diimide‐based n‐type polymers. In addition, the solar cells show an energy loss of 0.53 eV, the smallest value reported to date for all‐polymer solar cells with efficiency > 8%. These results demonstrate that fluorination of imide‐functionalized arenes offers an effective approach for developing new electron‐deficient building blocks with improved optoelectronic properties, and the emergence of f‐FBTI2 will change the scenario in terms of developing n‐type polymers for high‐performance all‐polymer solar cells.