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End-cap Group Engineering of a Small Molecule Non-Fullerene Acceptor: The Influence of Benzothiophene Dioxide

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... Cao et al. and our group have reported two NFAs with sulfonyl-based ending groups. 38,39 However, the device efficiency is lower than that of the ketone-based counterpart. In this work, we combine the sulfonyl-based ending groups with a 2,1,3-benzothiadiazolebased core to obtain a new NFA, BTP-IS. ...
... We also mentioned that the reported sulfonyl-based NFA (ITBC), which adopts an indacenodithieno[3,2-b]-thiophene (IDTT) core, exhibited very low electron mobility. 38 Compared to IDTT, the 2,1,3benzothiadiazole-based core has larger conjugated system and better planarity. Thus, the 2,1,3-benzothiadiazole-based core is beneficial to attenuate the steric hindrance of the sulfonyl groups. ...
... The balance charge transport should be vital in the OSCs with sulfonyl-based NFAs since the low-efficiency ITBC device exhibited a very poor balance in charge transport. 38 We then tested the J−V curves under different light intensities to assess the charge recombination. Generally, the relationship between J SC and light intensity (P) obeys a power law, J SC ∝ P α , where the exponent α value is related to bimolecular recombination. ...
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Ending groups play a vital role in regulating the band gap and energy level of low-band gap nonfullerene acceptors (NFAs). In this work, a novel NFA, BTP-IS, is synthesized by adopting sulfonyl-based ending groups. Compared to the ketone counterpart BTP-IC, BTP-IS exhibits a red-shift in absorption spectra with lower lowest unoccupied molecular orbital level. More importantly, the BTP-IS-based organic solar cells with PM6 as donor present a high power conversion efficiency (PCE) of 12.79%, which is much higher than that of the BTP-IC device (PCE of 7.54%). The efficient charge transfer between the polymer donor and NFA acceptor, the balance charge transport, and the fine photoactive morphology bear on the effective exciton dissociation and charge collection in the BTP-IS device, which induces high short circuit current (JSC) and fill factor (FF) values. This research has shed light on designing novel NFAs from the perspective of ending groups.
... In this investigation, femtosecond ND2PA spectroscopy (ND2PAS) is used to simultaneously obtain changes in ND2PA spectra and their respective magnitudes for all compounds (Figure 2) 34 and ITBC. 39 Steady-State Absorption Spectroscopy. UV−vis-NIR measurements were performed on a Shimadzu UV3101-PC dual arm spectrometer using 1 cm quartz cuvettes. ...
... 1−10 μM) for seven-ring, indacene-based compounds ITIC, ITIC3, F7IC, and ITBC are plotted in Figure 6. The reported reduction potentials for films of these compounds shift to increasingly reducing (more negative) potential in the order ITIC 31 < ITIC3 34 < F7IC 33 < ITBC, 39 suggesting that the acceptor strength of the end groups increases in the same order. Previous studies of quadrupolar A-D-A chromophores 10,48 show bathochromic shifts of the 1PA band with increasing acceptor strength; the successively bathochromically shifted 1PA and concomitantly increased M ge values in the present series, as summarized in Table 3, is consistent with this behavior and with the acceptor strength implied by the reduction potentials. ...
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The two-photon absorption (2PA) properties are investigated for two series of organic, π-conjugated, fused-ring, quadrupolar A-π-D-π-A chromophores of the type originally developed as non-fullerene acceptors for organic photovoltaics. These molecules are found to exhibit large nondegenerate two-photon absorption (ND2PA) cross-sections (ca. 6-27 × 10³ GM) in the near infrared (NIR). In the first series, involving molecules of varying core size, ND2PA spectra and cross-sections characterized by femtosecond ND2PA spectroscopy in chloroform solutions reveal that increases in core size, and thus conjugation length, leads to substantially red-shifted and enhanced 2PA. In a second series, variation of the strength of the terminal acceptor (A) with constant core size (7 rings, indacene-based) led to less dramatic variation in the 2PA properties. Among the two core types studied, compounds in which the donor has a thieno[3,2-b]thiophene center demonstrate larger 2PA cross-sections than their indacene-centered counterparts, due to the greater electron-richness of their cores amplifying intramolecular charge transfer. Excited-state absorption (ESA) contributions to nonlinear absorption measured by open-aperture Z-scans are deduced for some of the compounds by analyzing the spectral overlap between 2PA bands and NIR ESA transitions obtained by ND2PA and transient absorption measurements, respectively. ESA cross-sections extracted from transient absorption and irradiance-dependent open-aperture Z-scans are in reasonable agreement and their moderate magnitudes (ca. 10⁻²¹ m²) suggest that, although ESA contributions are non-negligible, the effective response is predominantly instantaneous 2PA.
... Synthesis of 2,5-Di(2-triisopropylsilylselenopheno[3,2-b]thiophen-5-yl)terephthalic Acid Diethyl Ester (7). To a two-neck flask were added 6 (15.8 g, 25 mmol), 2,5-dibromoterephthalic acid diethyl ester (4.56 g, 12 mmol), PdCl 2 (PPh 3 ) 2 (505 mg, 6 mol %), and anhydrous toluene (50 mL) under an argon atmosphere. ...
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A hexacyclic carbon-oxygen-bridged ladder-type unit, COi6, was developed. Three nonfullerene acceptors (COi6IC, COi6FIC and COi6DFIC) based on COi6 were prepared. They present low optical bandgaps of 1.31-1.37 eV and strong absorbance in the near-infrared region. A 9.12% power conversion efficiency was achieved from the solar cells based on COi6FIC and a wide-bandgap copolymer donor (FTAZ).
Article
Organic solar cells (OSCs) have been dominated by donor:acceptor blends based on fullerene acceptors for over two decades. This situation has changed recently, with non-fullerene (NF) OSCs developing very quickly. The power conversion efficiencies of NF OSCs have now reached a value of over 13%, which is higher than the best fullerene-based OSCs. NF acceptors show great tunability in absorption spectra and electron energy levels, providing a wide range of new opportunities. The coexistence of low voltage losses and high current generation indicates that new regimes of device physics and photophysics are reached in these systems. This Review highlights these opportunities made possible by NF acceptors, and also discuss the challenges facing the development of NF OSCs for practical applications.
Article
Bulk-heterojunction organic photovoltaic materials containing nonfullerene acceptors (NFAs) have seen remarkable advances in the past year, finally surpassing fullerenes in performance. Indeed, acceptors based on indacenodithiophene (IDT) have become synonymous with high power conversion efficiencies (PCEs). Nevertheless, NFAs have yet to achieve fill factors (FFs) comparable to those of the highest-performing fullerene-based materials. To address this seeming anomaly, this study examines a high efficiency IDT-based acceptor, ITIC, paired with three donor polymers known to achieve high FFs with fullerenes, PTPD3T, PBTI3T, and PBTSA3T. Excellent PCEs up to 8.43% are achieved from PTPD3T:ITIC blends, reflecting good charge transport, optimal morphology, and efficient ITIC to PTPD3T hole-transfer, as observed by femtosecond transient absorption spectroscopy. Hole-transfer is observed from ITIC to PBTI3T and PBTSA3T, but less efficiently, reflecting measurably inferior morphology and nonoptimal energy level alignment, resulting in PCEs of 5.34% and 4.65%, respectively. This work demonstrates the importance of proper morphology and kinetics of ITIC → donor polymer hole-transfer in boosting the performance of polymer:ITIC photovoltaic bulk heterojunction blends.
Article
We compared indacenodithiophene(IDT)-based fused-ring electron acceptor IDIC1 with its counterpart IHIC1 in which the central benzene unit is replaced by naphthalene unit, and investigated effects of benzene/naphthalene core on optical and electronic properties as well as performance of organic solar cells (OSCs). Compared with benzene-cored IDIC1, naphthalene-cored IHIC1 has a larger π-conjugation with stronger intermolecular π-π stacking. Relative to benzene-cored IDIC1, naphthalene-cored IHIC1 shows a higher lowest unoccupied molecular orbital energy level (IHIC1: −3.75 eV, IDIC1: –3.81 eV) and a higher electron mobility (IHIC1: 3.0 × 10−4 cm2 V−1 s−1, IDIC1: 1.5 × 10−4 cm2 V−1 s−1). When paired with the polymer donor FTAZ that has matched energy levels and complementary absorption spectrum, IHIC1-based OSCs show higher values in open-circuit voltage, short-circuit current density, fill factor and power conversion efficiency relative to the IDIC1-based control devices. These results demonstrate that extending benzene in IDT to naphthalene is a promising approach to upshift energy levels, enhance electron mobility, and finally achieve higher efficiency in nonfullerene acceptor-based OSCs.
Article
The post-fullerene indacenodithiophene acceptor ITIC is a highly effective n-type component of high-performance bulk-heterojunction (BHJ) polymer solar cells (PSCs) for reasons that are not well-understood. Here, the impact of the ITIC alkyl sub-stituent architecture on PSC active layer film morphology, charge transport, and photovoltaic (PV) performance is investigated with the donor polymers PBDB-T and PBDB-TF. On progressing from n-propyl to n-hexyl to n-nonyl ITIC substituents, PSC power conversion efficiency (PCE) increases from <0.1 % to 9.31% to 10.24%, respectively. BHJ blend morphology, carrier recombina-tion dynamics, and PV performance with both donor polymers as probed by AFM, XRD, GIWAXS, and light intensity dependence correlate with marked differences in ITIC acceptor crystallinity. The DSC cold crystallization temperatures of the n-hexyl and n-nonyl-functionalized acceptors are found to closely track the anneal-ing temperatures for optimum PSC performance. These results identify a promising strategy for optimizing the performance of post-fullerene acceptor PSCs.
Article
Naphtho[1,2-b:5,6-b′]dithiophene is extended to a fused octacyclic building block, which is end capped by strong electron-withdrawing 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile to yield a fused-ring electron acceptor (IOIC2) for organic solar cells (OSCs). Relative to naphthalene-based IHIC2, naphthodithiophene-based IOIC2 with a larger π-conjugation and a stronger electron-donating core shows a higher lowest unoccupied molecular orbital energy level (IOIC2: −3.78 eV vs IHIC2: −3.86 eV), broader absorption with a smaller optical bandgap (IOIC2: 1.55 eV vs IHIC2: 1.66 eV), and a higher electron mobility (IOIC2: 1.0 × 10−3 cm2 V−1 s−1 vs IHIC2: 5.0 × 10−4 cm2 V−1 s−1). Thus, IOIC2-based OSCs show higher values in open-circuit voltage, short-circuit current density, fill factor, and thereby much higher power conversion efficiency (PCE) values than those of the IHIC2-based counterpart. In particular, as-cast OSCs based on FTAZ: IOIC2 yield PCEs of up to 11.2%, higher than that of the control devices based on FTAZ: IHIC2 (7.45%). Furthermore, by using 0.2% 1,8-diiodooctane as the processing additive, a PCE of 12.3% is achieved from the FTAZ:IOIC2-based devices, higher than that of the FTAZ:IHIC2-based devices (7.31%). These results indicate that incorporating extended conjugation into the electron-donating fused-ring units in nonfullerene acceptors is a promising strategy for designing high-performance electron acceptors.
Article
Donor polymer fluorination has proven to be an effective method to improve the power conversion efficiency of fullerene-based polymer solar cells (PSCs). However, this fluorine effect has not been well-studied in systems containing new, non-fullerene acceptors (NFAs). Here, we investigate the impact of donor polymer fluorination in NFA-based solar cells by fabricating devices with either a fluorinated conjugated polymer (FTAZ) or its non-fluorinated counterpart (HTAZ) as the donor polymer and a small molecule NFA (ITIC) as the acceptor. We found that, similar to fullerene-based devices, fluorination leads to an increased open circuit voltage (Voc) from the lowered HOMO level and improved fill factor (FF) from the higher charge carrier mobility. More importantly, donor polymer fluorination in this NFA-based system also led to a large increase in short circuit current (Jsc), which stems from the improved charge transport and extraction in the fluorinated device. This study demonstrates that fluorination is also advantageous in NFA-based PSCs and may improve performance to a higher extent than in fullerene-based PSCs. In the context of other recent reports on demonstrating higher photovoltaic device efficiencies with fluorinated materials, fluorination appears to be a valuable strategy in the design and synthesis of future donors and acceptors for PSCs.
Article
A fused-ring thiophene-thieno[3,2-b]thiophene-thiophene (4T)-based low-band gap electron acceptor, 4TIC, has been designed and synthesized for non-fullerene solar cells. The utilization of the 4T center core enhances the charge mobility of 4TIC and extends its absorption band edge to 900 nm, which facilitates its function as a very efficient low-band gap electron acceptor. The rigid, conjugated framework of 4T also offers a lower reorganization energy to facilitate lower VOC energy loss. Femtosecond transient spectroscopy showed a level of polaron generation in 4TIC results in the more efficient transfer of energetic carriers higher than that seen with the benchmarked molecule, ITIC. Film morphology analysis has also shown that 4TIC has structural order that is more prominent than that of ITIC with a multiscale phase separation in the blend with donor polymer PTB7-Th. As a result, solar cells based on PTB7-Th and 4TIC exhibit a high power conversion efficiency of 10.43% and a relatively low non-ideal photon energy loss of 0.33 V. The low band gap and small energy loss make 4TIC suitable for tandem solar cells as a back-cell to reduce the transmission loss. As a demonstration, we fabricated series connection tandem solar cells incorporating 4TIC, which exhibts a high device performance of 12.62%.
Article
Fullerene-free OSCs employing n-type small molecules or polymers as the acceptors have recently experienced a rapid rise with efficiencies exceeding 12%. Owing to the good optoelectronic and morphological tunabilities, non-fullerene acceptors exhibit great potential for realizing high-performance and practical OSCs. In this Review, recent exciting progress made in developing highly efficient non-fullerene acceptors is summarized, mainly correlating factors like absorption, energy loss and morphology of new materials to their correspondent photovoltaic performance.
Article
Side group of ITIC-like small molecular acceptor (SMA) plays a critical role in crystallization property. In this article, two new SMAs with n-hexylthienyl and n-hexylselenophenyl as side chain, namely ITCPTC-Th and ITCPTC-Se, are designed and synthesized by employing newly developed thiophene-fused ending group (CPTCN). And thiophene and selenophene side group substituted effects of SMA-based fullerene-free polymer solar cells (PSCs) are investigated. A stronger σ-inductive effect between selenophene side group and electron-donating backbone endows ITCPTC-Se with better optical absorption and higher LUMO level, ITCPTC-Th-based PSCs deliver a higher power conversion efficiency of 10.61%. Charge transport and collection, recombination loss mechanism, and morphology of blend films are intensively studied. These results confirm that side group substituted effects of SMAs are multiple and thiophene is a superior option to selenophene as aromatic side group of ITIC-like SMAs.
Article
A A new small molecule, ITTC, bearing indacenodithieno[3,2-b]thiophene core and 2-(6-oxo-5,6-dihydro-4H-cyclopenta[c]thiophen-4-ylidene)malononitrile end group, was designed, synthesized and characterized as non-fullerene electron acceptor. The ITTC possesses strong and broad light absorption, high and balanced charge mobility and nanoscale interpenetrating morphology when blending with a recently synthesized hexafluoroquinoxaline based polymer donor-HFQx-T. HFQx-T was obtained from a Stille coupling copolymerization of 2, 6-bis(trimethyltin)-4,8-bis(5-(2-ethylhexyl)thiophene-2-yl)benzo[1,2-b:4,5-b’]dithiophene electron donating unit and hexafluoroquinoxaline based electron accepting unit. The device employing HFQx-T as donor and ITTC as acceptor delivered a power conversion efficiency (PCE) of 8.19% without any post-treatment. After thermal annealing, an impressive PCE of 10.4% was obtained. This performance is among the highest PCEs reported for fullerene-free polymer solar cells up to date. This study demonstrates the great potential of ITTC as n-type material for organic electronics.
Article
The past decade has witnessed significant advances in the field of organic solar cells (OSCs). Ongoing improvements in the power conversion efficiency of OSCs have been achieved, which were mainly attributed to the design and synthesis of novel conjugated polymers with different architectures and functional moieties. Among various conjugated polymers, the development of wide-bandgap (WBG) polymers has received less attention than that of low-bandgap and medium-bandgap polymers. Here, we briefly summarize recent advances in WBG polymers and their applications in organic photovoltaic (PV) devices, such as tandem, ternary, and non-fullerene solar cells. Addtionally, we also dissuss the application of high open-circuit voltage tandem solar cells in PV-driven electrochemical water dissociation. We mainly focus on the molecular design strategies, the structure-property correlations, and the photovoltaic performance of these WBG polymers. Finally, we extract empirical regularities and provide invigorating perspectives on the future development of WBG photovoltaic materials.
Article
Development of high-performance donor–acceptor (D–A) copolymers is vital in the research of polymer solar cells (PSCs). In this work, a lowbandgap D–A copolymer based on dithieno[3,2-b:2′,3′-d]pyridin-5(4H)-one unit (DTP), PDTP4TFBT, is developed and used as the donor material for PSCs with PC71BM or ITIC as the acceptor. PDTP4TFBT:PC71BM and PDTP4TFBT:ITIC solar cells give power conversion efficiencies (PCEs) up to 8.75% and 7.58%, respectively. 1,8-Diiodooctane affects film morphology and device performance for fullerene and nonfullerene solar cells. It inhibits the active materials from forming large domains and improves PCE for PDTP4TFBT:PC71BM cells, while it promotes the aggregation and deteriorates performance for PDTP4TFBT:ITIC cells. The ternary-blend cells based on PDTP4TFBT:PC71BM:ITIC (1:1.2:0.3) give a decent PCE of 9.20%.
Article
A new acceptor–donor–acceptor-structured nonfullerene acceptor ITCC (3,9-bis(4-(1,1-dicyanomethylene)-3-methylene-2-oxo-cyclopenta[b]thiophen)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d′:2,3-d′]-s-indaceno[1,2-b:5,6-b′]-dithiophene) is designed and synthesized via simple end-group modification. ITCC shows improved electron-transport properties and a high-lying lowest unoccupied molecular orbital level. A power conversion efficiency of 11.4% with an impressive V OC of over 1 V is recorded in photovoltaic devices, suggesting that ITCC has great potential for applications in tandem organic solar cells.
Article
The device efficiency of polymer:fullerene bulk heterojunction solar cells has recently surpassed 11%, as a result of synergistic efforts among chemists, physicists, and engineers. Since polymers are unequivocally the "heart" of this emerging technology, their design and synthesis have consistently played the key role in the device efficiency enhancement. In this article, the first focus is a discussion on molecular engineering (e.g., backbone, side chains, and substituents), then the discussion moves on to polymer engineering (e.g., molecular weight). Examples are primarily selected from the authors contributions; yet other significant discoveries/developments are also included to put the discussion in a broader context. Given that the synthesis, morphology, and device physics are inherently related in explaining the measured device output parameters (Jsc , Voc and FF), we will attempt to apply an integrated and comprehensive approach (synthesis, morphology, and device physics) to elucidate the fundamental, underlying principles that govern the device characteristics, in particular, in the context of disclosing structure-property correlations. Such correlations are crucial to the design and synthesis of next generation materials to further improve the device efficiency.
Article
Low bandgap n-type organic semiconductor (n-OS) ITIC has attracted great attention for the application as acceptor with medium bandgap p-type conjugated polymer as donor in non-fullerene polymer solar cells (PSCs) because of its attractive photovoltaic performance. Here we report a modification on the molecular structure of ITIC by side chain isomerization with meta-alkyl-phenyl substitution, m-ITIC, to further improve its photovoltaic performance. Compared with its isomeric counterpart ITIC with para-alkyl-phenyl substitution, m-ITIC shows a higher film absorption coefficient, a larger crystalline coherence and higher electron mobility. These inherent advantages of m-ITIC resulted in a higher power conversion efficiency (PCE) of 11.77% for the non-fullerene PSCs with m-ITIC as acceptor and a medium bandgap polymer J61 as donor, which is significantly improved over that (10.57%) of the corresponding devices with ITIC as acceptor. To the best of our knowledge, the PCE of 11.77% is one of the highest values reported in literatures to date for non-fullerene PSCs. More importantly, m-ITIC-based device shows less thickness-dependent photovoltaic behavior than ITIC-based devices in the active-layer thickness range of 80~360 nm, which is beneficial for large area device fabrication. These results indicate that m-ITIC is a promising low bandgap n-OS for the application as acceptor in PSCs and the side chain isomerization could be an easy and convenient way to further improve the photovoltaic performance of the donor and acceptor materials for high efficiency PSCs.
Article
Herein, we design and synthesize a perylene diimide derivative with a fully fused backbone, FITP, which possesses an elevated lowest unoccupied molecular orbital level and high electron mobility. Consequently, polymer solar cells with FITP as the acceptor can provide the best efficiency of 7.33% with a high voltage of 0.99 V.
Article
From hybrid perovskites to semiconducting polymer/fullerene blends for organic photovoltaics, many new materials being explored for energy harvesting and storage exhibit performance characteristics that depend sensitively on their nanoscale morphology. At the same time, rapid advances in the capability and accessibility of scanning probe microscopy methods over the past decade have made it possible to study processing/structure/function relationships ranging from photocurrent collection to photocarrier lifetimes with resolutions on the scale of tens of nanometers or better. Importantly, such scanning probe methods offer the potential to combine measurements of local structure with local function, and they can be implemented to study materials in situ or devices in operando to better understand how materials evolve in time in response to an external stimulus or environmental perturbation.
Article
A nonfullerene-based polymer solar cell (PSC) which significantly outperforms fullerene-based PSCs with respect to the power-conversion efficiency is demonstrated for the first time. An efficiency >11%, which is among the top values in the PSC field, and excellent thermal stability is obtained using PBDB-T and ITIC as donor and acceptor, respectively.
Article
We develop an efficient fused-ring electron acceptor (ITIC-Th) based on indacenodithieno[3,2-b]thiophene core and thienyl side-chains for organic solar cells (OSCs). Relative to its counterpart with phenyl side-chains (ITIC), ITIC-Th shows lower energy levels (ITIC-Th: HOMO = -5.66 eV, LUMO = -3.93 eV; ITIC: HOMO = -5.48 eV, LUMO = -3.83 eV) due to the σ-inductive effect of thienyl side-chains, which can match with high-performance narrow-bandgap polymer donors and wide-bandgap polymer donors. ITIC-Th has higher electron mobility (6.1 X 10-4 cm2 V-1 s-1) than ITIC (2.6 X 10-4 cm2 V-1 s-1) due to enhanced intermolecular interaction induced by sulfur-sulfur interaction. We fabricate OSCs by blending ITIC-Th acceptor with two different low-bandgap and wide-bandgap polymer donors. In one case a power conversion efficiency of 9.57% was observed, which rivals some of the highest efficiencies for single junction OSCs based on fullerene acceptors.
Article
Non-fullerene organic solar cells (NF-OSCs), in which an n-type organic molecule instead of a fullerene derivative is utilized as the electron-acceptor material, have recently emerged as a new topic in the field of organic solar cells. Replacement of the traditional fullerene acceptor in the photoactive layer of a normal organic solar cell with the organic acceptor gives rise to several advantages, like light absorption and energy level tunability, diversity of donor-to-acceptor combination, and large-scale production of acceptor materials. Studies on NF-OSCs can be traced back to 1986, when the first bilayered organic solar cell was proposed. Unfortunately, they has been advancing very slowly and the power-conversion-efficiency (PCE) was only approaching or exceeding 2% up to 2012. Fast advances have been driven forward since 2013, when the PCE value first broke through 4%, and the reported PCE value has now reached about 8% after a short period of 3 years. If we turn to natural systems such as the photosynthesis systems I and II, in which Nature utilizes organic molecules to accomplish high-efficiency solar-to-chemical energy conversion through the cascade unidirectional electron-hole transfer paths, we can rationally expect an even higher PCE and a convincing future for NF-OSCs. In this review, we will address recent new progress in this sub-branch of organic solar cells.
Article
In the past two years, non-fullerene acceptors including polymers and small molecules have become the focus of many research efforts. Fullerene-free organic solar cells (OSCs) have shown efficiencies of up to 6.8% for solution-processed devices, and even up to 8.4% for vacuum-deposited devices, which have been significantly improved relative to those disclosed 2 years ago (generally <4%). Non-fullerene acceptor materials are a new focus in the OSC field. Tailoring extended fused-rings with electron-deficient groups is an effective strategy for design of acceptors. Here, very recent developments in several systems of fused ring-based electron acceptors, such as halogenated (sub or subna)phthalocyanine, imide-functionalized rylene, and linear fused-rings end capped with electron deficient blocks, are reviewed.
Article
The study emphasizes the correlation between chemical structures, physical properties, and resulting device performance of the solution-processed polymers/small molecules, and tries to provide a comprehensive understanding from materials design to a variety of device applications. To achieve near-IR absorbing/emitting abilities, strong donor-acceptor interaction and stabilization of the quinoid resonant structure are required. However, due to the smaller one-dimensional quantum well length, bandgap lowering is more difficult and normally requires very strong donor or acceptor units in the case of small molecules. Anthopoulos and Patil showed that the triethylene glycol side chain can enhance molecular self-assembly and increase the FET mobility for DPP-based polymers. Gong applied PS-TPD-PFCB, a commonly used electron-blocking material in light-emitting diodes, in a novel IR photodetector and realized very low dark current and high detection sensitivity. Yang and Li's recent work shows a clear link between the polymers' molecular compatibility (preferred orientations) and the resulting multidonor system morphology, which has a profound impact on the carrier transport and device efficiency.
Article
A novel non-fullerene electron acceptor (ITIC) that overcomes some of the shortcomings, for example, weak absorption in the visible spectral region and limited energy level variability, of fullerene acceptors is designed and synthesized. Fullerene-free polymer solar cells (PSCs) based on the ITIC acceptor are demonstrated to exhibit power conversion efficiencies of up to 6.8%, a record for fullerene-free PSCs. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Article
A new push–pull molecule, containing an (alkylamino)thiophene as electron donor and 1,3-bis(dicyanomethylidene)-2-indenylindene as electron acceptor, has been synthesized and characterized in the solid state by X-ray crystallography, in solution by UV/Vis and NMR spectroscopy and by theoretical calculations. The quinoidal zwitterionic form of this compound was underscored both in the solid state and in moderately polar solvents. Experimental and theoretical analyses were also performed on two similar push–pull molecules, selectively chosen to vary basic chemical features such as the resonance energy of the aromatic group and the steric hindrance of the attractor. Comparative analysis of the three compounds has shown that steric hindrance, resonance energy and the polarity of the environment play a significant role in stabilizing one limiting resonance form over the other. By varying these chemical variables, fine tuning of the electronic ground state of a push–pull molecule, from the neutral aromatic form to the charge-separated zwitterion, passing through a form in which the two limiting forms contribute almost equally (the cyanine limit), can be achieved.
Article
Different strategies for the synthesis of 2′-hydroxy-4′-methylsulfonylacetophenone are reported in the present paper. This compound is considered as a key synthon for the synthesis of new flavonoid derivatives designed as potential cyclooxygenase-2 inhibitors. The retrosynthetic approach via 3′-methylsulfonylacetophenone, which included three synthetic pathways, did not allow us to obtain the expected compound. However, a synthesis from 3-mercaptophenol led to the desired acetophenone in three steps: thiophenol methylation, Friedel–Crafts acetylation and oxidation of the sulphide to the corresponding sulfone. The desired compound, 2′-hydroxy-4′-methylsulfonylacetophenone, will be used as a synthon for the preparation of novel flavonoid derivatives, such as 2′-hydroxychalcones, flavanones, flavones, and flavonols.
Article
Careful selection of processing solvents to tune optimal active layer morphology in a donor-acceptor copolymer blend [PTB7:P(NDI2OD-T2)] yields bulk heterojunction microstructures with intradomain percolative pathways and enhanced charge transport. Such microstructures afford all-polymer solar cells with power conversion efficiencies as high as 2.7%.
Article
The synthesis of a series of bright deeply colored styryl dyes derived from the title compounds and various aromatic and heteroaromatic aldehydes is described. Some of the dyes were subjected to oxidative cyanation to obtain the cyanated analogues. The absorption-emission spectra of the dyes were recorded and the dyeing properties on polyester of some of the dyes was studied.
Article
Second-order non-linear optical (NLO) poly(phenylquinoxalines) with high glass transition temperatures were prepared by reaction of bis(1,2-diketone)chromophore monomer and a tetramine at room temperature. Glass transition temperatures in the range of 187–260 °C were obtained. Thin spincoated films of the polymers were corona-poled and analysed by second-harmonic generation (SHG). Second-order susceptibility values d33(ω) up to 114 pm/V were obtained. Poled order stability measurements over a period of 750 h resulted in up to 91% of remaining NLO-response at 125 °C.