Naphthalene-Diimide-Based Ionenes as Universal Interlayers for Efficient Organic Solar Cells

Fluorinated Naphthalene Diimides as Buried Electron Transport Materials Achieve Over 23% Efficient Perovskite Solar Cells

Naphthalene diimides (NDI) are widely serving as the skeleton to construct electron transport materials (ETMs) for optoelectronic devices. However, most of the reported NDI-based ETMs suffer from poor interfaces with the perovskite which deteriorates the carrier extraction and device stability. Here, a representative design concept for editing the peripheral groups of NDI molecules to achieve multifunctional properties is introduced. The resulting molecule 2,7-bis(2,2,3,3,4,4,4-heptafluorobutyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (NDI-C4F) incorporated with hydrophobic fluorine units contributes to the prevention of excessive molecular aggregation, the improvement of surface wettability and the formation of strong chemical coordination with perovskite precursors. All these features favor retarding the perovskite crystallization and achieving superior buried interfaces, which subsequently promote charge collection and improve the structural compatibility between perovskite and ETMs. The corresponding PSCs based on low-temperature processed NDI-C4F yield a record efficiency of 23.21%, which is the highest reported value for organic ETMs in n-i-p PSCs. More encouragingly, the unencapsulated devices with NDI-C4F demonstrate extraordinary stability by retaining over 90% of their initial PCEs after 2600 h in air. This work provides an alternative molecular strategy to engineer the buried interfaces and can trigger further development of organic ETMs toward reliable PSCs.

Interface Engineering for Highly Efficient Organic Solar Cells

Organic solar cells (OSCs) have made dramatic advancements during the past decades owing to the innovative material design and device structure optimization, with power conversion efficiencies surpassing 19% and 20% for single-junction and tandem devices, respectively. Interface engineering, by modifying interface properties between different layers for OSCs, has become a vital part to promote the device efficiency. It is essential to elucidate the intrinsic working mechanism of interface layers, as well as the related physical and chemical processes that manipulate device performance and long-term stability. In this article, the advances in interface engineering aimed to pursue high-performance OSCs are reviewed. The specific functions and corresponding design principles of interface layers are summarized first. Then, the anode interface layer, cathode interface layer in single-junction OSCs, and interconnecting layer of tandem devices are discussed in separate categories, and the interface engineering-related improvements on device efficiency and stability are analyzed. Finally, the challenges and prospects associated with application of interface engineering are discussed with the emphasis on large-area, high-performance, and low-cost device manufacturing.

Novel Polyelectrolytes Based on Naphthalene Diimide with Different Counteranions for Cathode Interlayers in Polymer Solar Cells

We synthesized novel polyelectrolytes based on naphthalene diimide with quaternary amine featuring hydroxyl groups at the side chain, along with different counteranions (PF-NDIN-Br-OH and PF-NDIN-I-OH) for polymer solar cell (PSC) application as the interlayer. The polyelectrolytes establish a beneficial interface dipole through the ionic moieties and synergistic effects arising from the hydroxyl groups located at the side chain. Incorporating polyelectrolytes as the cathode interlayer resulted in an enhancement of the power conversion efficiency (PCE). The PCE of the device with PF-NDIN-Br-OH increased from 8.96% to 9.51% compared to the ZnO-only device. The best PCE was obtained with the device based on PF-NDIN-I-OH, up to 9.59% resulting from the Jsc enhancement. This outcome implies a correlation between the performance of the device and the synergistic effects observed in polyelectrolytes containing hydroxyl groups in the side chain, along with larger anions when employed in PSCs.

Solution-Processed Semiconductor Materials as Cathode Interlayers for Organic Solar Cells

Cathode interlayers (CILs) play a crucial role in improving the photovoltaic efficiency and stability of OSCs. CILs generally consists of two kinds of materials, interfacial dipole-based CILs and SPS-based CILs. With good charge transporting ability, excellent compatibility with large-area processing methods, and highly tunable optoelectronic properties, the SPS-based CILs exhibit remarkable superiorities to their interfacial dipole-based counterparts in practical use, making them promising candidate in developing efficient CILs for OSCs. This mini-review highlights the great potential of SPS-based CILs in OSC applications and elucidates the working mechanism and material design strategy of SPS materials. Afterward, the SPS-based CIL materials are summarized and discussed in four sections, including organic small molecules, conjugated polymers, nonconjugated polymers, and TMOs. The structure-property-performance relationship of SPS-based CIL materials is revealed, which may provide readers new insight into the molecular design of SPS-based CILs. The mechanisms to endow SPS-based CILs with thickness insensitivity, resistance to environmental erosion, and photo-electric conversion ability are also elucidated. Finally, after a brief summary, the remaining issues and the prospects of SPS-based CILs are suggested.

Cathode Interlayer Based on Naphthalene Diimide: A Modification Strategy for Zinc-Oxide-Free Inverted Organic Solar Cells

Perylene diimide with ammonium oxide as a terminal group (named PDIN-O) is a well-known cathode interlayer in conventional-type organic solar cells (OSCs). Since naphthalene diimide exhibits a lower LUMO level than perylene diimide, we chose it as a core to further control the LUMO level of the materials. Small molecules (SMs) produce a beneficial interfacial dipole by the end of ionic functionality at the side chain of naphthalene diimide. With the active layer based on a nonfullerene acceptor (PM6:Y6BO), the power conversion efficiency (PCE) is enhanced by utilizing SMs as cathode interlayers. We discovered that the inverted-type OSC with naphthalene diimide with oxide as a counteranion (NDIN-O) shows poor thermal stability, which can cause irreversible damage to the interlayer-cathode contact, leading to poor PCE (11.1%). To overcome the disadvantage, we introduce NDIN-Br and NDIN-I with a higher decomposition temperature. An excellent PCE of 14.6% was achieved with the device based on NDIN-Br as an interlayer, which is almost the same as the PCE of the ZnO-based device (15.0%). The device based on NDIN-I without the ZnO layer exhibits an improved PCE of 15.4%, which is slightly higher than the ZnO-based device. The result offers a replacement of the ZnO interlayer, which is necessary to carefully manage the sol-gel transition by annealing temperatures as high as 200 °C and leading to low-cost manufacture of OSCs.

Self-Doping Naphthalene Diimide Conjugated Polymers for Flexible Unipolar n-Type OTFTs

The development of high-performance organic thin-film transistor (OTFT) materials is vital for flexible electronics. Numerous OTFTs are so far reported but obtaining high-performance and reliable OTFTs simultaneously for flexible electronics is still challenging. Herein, it is reported that self-doping in conjugated polymer enables high unipolar n-type charge mobility in flexible OTFTs, as well as good operational/ambient stability and bending resistance. New naphthalene diimide (NDI)-conjugated polymers PNDI2T-NM17 and PNDI2T-NM50 with different contents of self-doping groups on their side chains are designed and synthesized. The effects of self-doping on the electronic properties of resulting flexible OTFTs are investigated. The results reveal that the flexible OTFTs based on self-doped PNDI2T-NM17 exhibit unipolar n-type charge-carrier properties and good operational/ambient stability thanks to the appropriate doping level and intermolecular interactions. The charge mobility and on/off ratio are fourfold and four orders of magnitude higher than those of undoped model polymer, respectively. Overall, the proposed self-doping strategy is useful for rationally designing OTFT materials with high semiconducting performance and reliability.

A low-cost naphthaldiimide based organic cathode for rechargeable lithium-ion batteries

Recently, the development of cathode materials is becoming an important issue for lithium-ion batteries (LIBs). Compared with inorganic cathodes, the organic cathodes are developing rapidly, ascribing to their distinct merits in light weight, low cost, massive organic resources and high capacity. In this paper, a cost-efficiency naphthaldiimide (NDI) based derivative, 2,7-bis(2-((2-hydroxyethyl) amino) ethyl) benzo[lmn] [3,8] phenanthroline-1,3,6,8(2H, 7H)-tetraone (NDI-NHOH), was used as organic cathode in LIBs. The NDI-NHOH was synthesized easily via one-step process, and it showed very high thermal stability. Through mixing NDI-NHOH with acetylene black and polyvinylidene fluoride (weight ratio of 6:3:1) as composite cathode in lithium-metal based LIBs, the NDI-NHOH presented versatile electrochemical properties. From cyclic voltammetry (CV) test, it exhibited two reversible peaks for oxidation and reduction in the first cycle, respectively. Notably, the oxidation and reduction peaks were located at 2.54, 3.22 and 2.14, 2.32 V vs. Li+/Li, respectively. By employing NDI-NHOH as cathode, it demonstrated a specific capacity of about 80 mAh g-1 in the range of 1.5-3.5 V, where the batteries retained a capacity retention of 50% over 20 cycles. According to the LIBs study, it suggests that the NDI-NHOH-based derivative shows a potentially promising candidate as efficient organic cathode materials for high-performance metal-ions batteries.

Promoting the Efficiency and Stability of Nonfullerene Organic Photovoltaics by Incorporating Open-Cage [60]Fullerenes in the Nonfullerene Nanocrystallites

The device efficiency of PM6:Y6-based nonfullerene organic solar cells is fast advanced recently. To maintain organic solar cells (OSCs) with high power conversion efficiency over 16% in long-term operation, however, remains a challenge. Here, a novel non-volatile additive, an open-cage [60]fullerene (8OC₆₀Me), is incorporated into PM6:Y6-based OSCs for high-performance with high durability. With optimized addition of 1.0 wt % 8OC₆₀Me, the PCE value of PM6:Y6/8OC₆₀Me OSCs can be promoted to 16.5% from 15.0%. Most strikingly, such a high PCE performance can maintain nearly 100% for over 500 h at room temperature; at an elevated operation temperature of 80 °C, the PCE can be stabilized above 15.0% after 45 h of operation. Grazing incidence small- and wide- angle X-ray scattering studies reveal improved orientation and crystallinity of Y6 in a fractal-like network structure of PM6 in PM6:Y6/8OC₆₀Me films under in situ annealing, parallel to the enhanced electron mobility. Analysis of charge distributions lines up possible van der Waals interaction between the thienyl/carbonyl moiety of 8OC₆₀Me and difluorophenyl-based FIC-end groups of Y6. This result is of great contrast to those devices with the best-selling PC₆₁BM as the additives─8OC₆₀Me might be of interest to be incorporated into future Y6-based OSCs for concomitantly improved PCE and excellent stability.

Comparison of Constituents and Antioxidant Activity of Above-Ground and Underground Parts of Dryopteris crassirhizoma Nakai Based on HS-SPME-GC-MS and UPLC/Q-TOF-MS

Dryopteris crassirhizoma Nakai is a Chinese traditional medicinal fern plant for heat-clearing and detoxifying, promoting blood circulation and dissipating blood stasis. Previous researches showed that many factors could influence the components of medicinal plants, and the plant part is one of the main factors. So far, only the underground part of D. crassirhizoma, called “Mianma Guanzhong”, has been widely sold in the market. However, the above-ground part was usually at low utilization, resulting in a waste of medicinal resources. In order to further develop and utilize the medicinal resources of D. crassirhizoma, the constituents, total flavonoid contents and antioxidant activity of the above-ground and underground parts of D. crassirhizoma were tentatively analyzed and compared based on HS-SPME-GC-MS and UPLC/Q-TOF-MS. The results showed that (1) the volatile components were mainly focused in the above-ground part of D. crassirhizoma, including 3-carene, isoledene, ionene, 4-amino-1-naphthol and furfural. (2) Nonvolatile components of the underground part of D. crassirhizoma contained phenolic acid, flavonoids, phloroglucinol and less fatty acid. (3) The common compounds of the above-ground and underground parts of D. crassirhizoma were phenolic acid and flavaspidic acid AB. (4) Antioxidant activity of the underground part was stronger than that of the above-ground part of D. crassirhizoma. In conclusion, both the above-ground and underground parts of D. crassirhizoma are important medicinal resources worthy of further development.

Achieving the low interfacial tension by balancing crystallization and film-forming ability of the cathode interlayer for organic solar cells

A series of molecules with imide units bridged by the core of thiophene-based groups, namely N-dimethylaminopropyl-4-thiophene-1,8- naphthalimide (NT), bis(N-dimethylaminopropyl)-4-thiophene-1,8-naphthalimide (NTN), and bis(N-dimethylaminopropyl)-4-bithiophene-1,8-naphthalimide (N2TN), have been reported as cathode interfacial materials (CIMs) to realize low interfacial tension with the blend in organic solar cells (OSCs). We evaluated the Ohmic contact between the active layer and these cathode interlayers basedon various characterizations, which is of great significance for further understanding these imide-based interlayers. It turned out that the homogeneous and continuous NTN interlayer as a CIM balanced the factors of crystallization and film-forming property, and broke through the limitation of poor conductivity and high aggregation in our previous work. Moreover, compared with NT and N2TN, the NTN interlayer achieve a combination of good solubility in methanol, efficient electron mobility, and aligned work function. These advantages of NTN are conducive to the realization of high-efficient interfacial electron collection and transfer, thus improving the short-circuit current density (J_SC) and filling factor (FF) of devices. Therefore, the binary OSCs (PM6:Y6) based on NTN engineered aluminium-cathode with excellent stability demonstrate a maximum power conversion efficiency (PCE) of 16.56 %, which is higher than NT (PCE = 1.34 %) and N2TN (PCE = 13.90 %). The enhanced performance is ascribed to the improvement of JSC and FF, which is originated from the outstanding conductivity and high-quality interface of NTN. Surprisingly, the PM6:Y6-based semitransparent device with NTN obtain a PCE of 13.43 % with an average visible transmittance of 17.79 %, which is better than traditional PDINO. This study highlights a potential strategy for enhancing the performance of OSCs by the interface engineering via decreasing the interfacial intension.

Combining ZnO and PDINO as a Thick Cathode Interface Layer for Polymer Solar Cells

Cathode interface layers (CILs) are important for electron extraction in polymer solar cells (PSCs). Currently, the thickness of CILs is often below 15 nm due to their low electron mobility, which is not favorable for large-scale fabrication. Herein, we report a thick CIL for efficient PSCs by modifying the ZnO nanocrystals (NCs) film with perylene diimides functionalized with amino oxide (PDINO). The combined ZnO NCs/PDINO CIL inherits the high electron mobility of ZnO NCs and dense morphology of PDINO, affording higher power conversion efficiencies (PCEs) of its devices than the sole component controls. The PSCs with the ZnO NCs/PDINO CIL also exhibit good tolerance to the CIL thickness, and the PM6:Y6 and PM6:BTP-eC9 devices can achieve high PCEs of over 15% at the CIL thickness of 70 nm. Further, the ZnO NCs/PDINO devices show better stability than those with sole ZnO NCs or PDINO. Our results provide a new way to construct potential CILs for high performance PSCs.

Polymerized naphthalimide derivatives as remarkable electron-transport layers for inverted organic solar cells

Two polymerized naphthalimide derivatives, named as N-TBHOB and N-DBH, have been prepared by quaternization, which exhibit excellent performance as electron-transport layers (ETLs) in inverted organic solar cells (i-OSCs). The results indicate N-TBHOB with a reticulated structure owns a superior performance on electron extraction, electron transport, thickness tolerance and less carrier recombination compared with N-DBH with linear structure. The i-OSCs based on N-TBHOB with PTB7-Th:PC₇₁ BM as the active layer achieve PCEs of 10.72% and 10.03% under the thickness of 11 and 48 nm respectively, which indicates N-TBHOB possesses better thickness tolerance than most of organic ETLs in i-OSCs. N-TBHOB also shows more competent performance than N-DBH and ZnO in non-fullerene i-OSCs for comprehensively improved J_sc , V_oc and FF values. Its i-OSC with PM6:Y6 blend presents a high PCE of 16.78%. The study provides an efficient strategy to prepare ETLs by combining conjugated and nonconjugated backbone with a reticulated structure for high-performance i-OSCs. This article is protected by copyright. All rights reserved.

Electroactive Ionenes: Efficient Interlayer Materials in Organic Photovoltaics

ConspectusOrganic photovoltaics (OPVs) have the advantages of being lightweight, mechanically flexible, and solution-processable over large areas, and for decades, they have been the focus of the academic and industrial communities. Recent progress in the design of high-performance organic semiconductors and device optimization has promoted solar cell efficiencies of up to 19%, showing great promise for commercialization. Optimally designed OPVs are achieved using a bicontinuous interpenetrating network of donor and acceptor materials in between two charge-collecting electrodes. Charge extraction and transport between metal electrodes and organic semiconductors are crucial to device operation. The energy-level mismatch when metal electrodes and organic semiconductors are in contact usually induces additional energy barriers and resultant inefficient charge transport and collection, leading to charge carrier recombination at the interface and inferior device performance. To align energy levels at the interface, interlayer materials and their integration into devices have emerged as a widely used strategy to promote the performance of solar cell devices. Interlayer materials have the ability to modify the work functions (WFs) of metal electrodes, holding the potential to enhance the built-in electrostatic field (V_bi) of the devices and suppress the charge recombination loss, which is beneficial to improving the open circuit voltage (V_OC), short circuit current density (J_SC), and fill factor (FF) of the solar cells.Organic interlayer materials have recently come into focus for fundamental study and practical development because of their diverse molecular design and superior solution processability. Tremendous effort has been devoted to exploring novel organic interlayer materials to achieve all-solution-processed multilayer solar cells. Such interlayer materials usually have orthogonal solubilities relative to the photoactive layer materials, working as multifunctional interfacial layers to manipulate the mechanical and electrical contacts in solar cell devices. Ionenes are a unique class of polyelectrolytes wherein the ionic species reside within the polymer backbone rather than as pendant groups. In ionenes, the charge density is high in comparison to that of other polyelectrolytes, and the periodicity of the charges is easily controlled, providing a tunable density of dipole moments. Ionenes can be readily synthesized from 3° diamines and α,ω-dihaloalkanes to generate polymer chains of ammonium cations connected by flexible hydrocarbon linkages with mobile anions. However, the requisite building blocks of ionenes are not limited to such molecules. Recent advances in combining ionenes with conjugated molecules to generate electroactive ionenes have catalyzed a great amount of interest in such polymers for organic electronic devices.In this Account, we first introduce the molecular design and synthesis of electroactive ionenes. Following this, we will discuss the mechanism and effect of ionenes on the modification of metal electrodes. We then review the strategies for controlling the morphology of ionene interlayers. Finally, we compare the doping effect, conductivity, and charge transport of some representative ionenes and their performance as interlayers in solar cell devices. We present our current understanding based on recent progress and outstanding issues of interlayer materials in OPVs and to propose future directions and opportunities.

Revival of Insulating Polyethylenimine by Creatively Carbonizing with Perylene into Highly Crystallized Carbon Dots as the Cathode Interlayer for High-Performance Organic Solar Cells

The development of new electron transporting layer (ETL) materials to improve the charge carrier extraction and collection ability between cathode and the active layer has been demonstrated to be an effective approach to enhance the photovoltaic performance of organic solar cells (OSCs). Herein, water-soluble carbon dots (CDs) as ETL material have been creatively synthesized by a vigorous chemical reaction between polyethylenimine (PEI) and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) via a simple one-step hydrothermal method. Taking full advantage of the high electron transfer property of PTCDA and the work function (W_F) reduction ability of PEI, CD gained high electron mobility due to its large π-conjugated area and reduced the W_F of indium tin oxide (ITO) by 0.75 eV. As for the photovoltaic performance of devices, inverted OSCs based on CDs have achieved a high power conversion efficiency (PCE) of 17.35%, exhibiting no burn-in effect with no reduction in PCE after more than 4000 h of storage. The successful application of CDs in OPV has developed a new avenue for designing efficient ETL materials that benefits the photovoltaic performance of OSCs.

A novel naphthalene diimide-based conjugated polymer as an electron transport material for non-fullerene organic solar cells

The only aliphatic amino side chains at the N-position of naphthalene diimide endow novel electron transport materials with good film-forming and interface modification properties, which improves the device efficiency and stability.

Gamma-aminobutyric acid-functionalized naphthalene diimide for aqueous organic flow batteries

Gamma-aminobutyric acid-functionalized naphthalene diimide (GABA-NDI) was synthesized and cycled in a flow battery coupled with ferrocyanide. The battery demonstrated a coulombic efficiency of 99.96% and an energy efficiency of 80.9% at 60 mA cm−2.

Aminonaphthalimide-Based Molecular Cathode Interlayers for As-Cast Organic Solar Cells

A series of imide-based small molecules, namely NA, NAA, and NEA with simple structures, were designed and synthesized by introducing different amine side-chains into the benzene unit of imide, which were used as cathode interfacial materials in organic solar cells (OSCs). The amine side-chain substitution positions were systematically investigated with these small-molecule imides. Compared with NA without amide chains-NAA, and NEA, with 3-dimethylaminopropylamine and ethylenediamine chains, respectively-show bathochromic shifts in absorption, decreased band gaps, and higher highest occupied molecular orbital (HOMO) energy levels. A power conversion efficiency (PCE) of 15.04 % was obtained with the NEA-based as-cast OSCs with a high open-circuit voltage and fill factor for PM6 : Y6 blend and the maximum PCE of 15.80 % was reached for as-cast PM6 : Y6 : IT-M ternary OSCs. NEA exhibits better conductivity, higher electron mobility, and stronger the capability of lower work function of cathode among three molecules, affording OSCs with better photovoltaic performance. Additionally, these three molecules show excellent thermal stability both in solution and in films at 150 °C. The results indicate that imide-based small molecules are promising cathode interfacial materials for commercial OSCs.

Boosting the Efficiency of Non-fullerene Organic Solar Cells via a Simple Cathode Modification Method

This work demonstrates a simple yet effective method to significantly improve the power conversion efficiency (PCE) of highly efficient non-fullerene organic solar cells by mixing two electron transport materials. The new electron transport layer shows an energy level better aligned with the active layer and an improved morphology that could reduce the active layer-electrode contact. These improvements lead to enhanced charge extraction, better charge selectivity, suppressed exciton recombination, and finally a boosted PCE in the PM6:Y6-based solar cells. When applied in conjunction with the non-halogenated solvent-processed PM6:PY-IT-based active layer, the mixed ETL also gives rise to a leading result for binary all-polymer solar cells (PCE of >16%) with a concurrent increase in V_OC, J_SC, and FF.

N-Type Self-Doped Hyperbranched Conjugated Polyelectrolyte as Electron Transport Layer for Efficient Nonfullerene Organic Solar Cells

The electron transport layer (ETL) exerts a dramatic influence on the power conversion efficiency (PCE) of the nonfullerene organic solar cells (NOSCs). Currently, the majority of the organic ETLs possess a relatively poor conductivity, which is not conducive to carrier transport and collection. Herein, we design and develop a novel hyperbranched conjugated polyelectrolyte (CPE) based on n-type perylene diimide (PDI) as the center core and quaternary ammonium salt as the side polar groups. The lone pair electrons of the nitrogen atoms can transfer to the electron deficient PDI core and endow the molecule with an efficient n-type self-doping effect. Moreover, the hyperbranched structure makes the molecule functionalized with more side polar groups, favoring forming more dipoles and stronger dipole moments. Therefore, the CPE PTPAPDINO possesses a high conductivity and can notably decrease the work function (WF) of the electrode, contributing to the carrier transport and collection of the device. The NOSC with PTPAPDINO as ETL delivers an excellent PCE of 15.62%, which is even superior to the device using the classical PDINO ETL. Moreover, the PCE can retain 82.6% of the optimal device when the thickness has been increased to 28 nm. These results manifest that it is a feasible strategy to design an n-type self-doping hyperbranched CPE as efficient ETL, and PTPAPDINO is a promising alternative ETL for high performance NOSCs.

Conductive Ionenes Promote Interfacial Self-Doping for Efficient Organic Solar Cells

Conductive ionenes were synthesized by integrating the electron donor dialkoxynaphthalene (DAN) with the electron acceptor naphthalene diimide (NDI) using the Menshutkin reaction. The crystallinity and morphology of the films of these polymers can be optimized by varying the DAN-to-NDI ratio. These ionenes show strong charge transfer from DAN to NDI, though absent conjugated backbones, affording self-doping polymers with enhanced π-π interactions and excellent electronic properties. This is the first example where an electron donor can dope the electron acceptor in nonconjugated polymers, opening a new avenue for designing efficient interlayer materials. These ionenes markedly modify the electrode interface and promote efficient interfacial self-doping to boost the performance of fullerene-based, non-fullerene-based, and ternary organic solar cells, affording high power conversion efficiencies over a wide range of interlayer thicknesses, from ∼8 to ∼40 nm, with a maximum efficiency of 17.05%.

Designing and theoretical study of fluorinated small molecule donor materials for organic solar cells

A recently synthesized photoactive donor named fluorinated thienyl-substituted benzodithiophene (DRTB-FT), modified with four novel end capped acceptor molecules, has been investigated through different electrical, quantum, and spectrochemical techniques for its enhanced electro-optical and photovoltaic properties. DRTB-FT was connected to 2-methylenemalononitrile (D-1), 2-methylene-3-oxobutanenitrile (D-2), 2-(2-methylene-3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile (D-3), and 3-methyl-5methylene-2-thioxothiazolidin-4-one (D-4) as terminal acceptor moieties. The architectural D-1 and D-3 molecules owe reduced optical band gap of 2.45 and 2.28 eV benefited from A-D-A configuration and have broaden maximum absorption band (λ_max) at 617 and 602 nm in polar organic solvent (chloroform). Reduced optical band gap sets the ease for enhanced absorption. Reorganization energy of electron (λ_e) of D-3 molecule (0.00397 eV) was smaller among all which disclosed its greater mobility of conducting electrons (ICT). Larger values of dipole moment (μ) of D-1 (5.939 Debye) and D-3 (3.661 Debye) molecules in comparison to R indicated greater solubilities of the targeted molecules. Among the tailored molecules, D-3 showed the lowest binding energy of 0.25 eV in solvent phase and 0.08 eV in gaseous phase. The voltaic strength of the designed molecules was examined with respect to fullerene derivative (PC₆₁BM) which exposed that D-1 is the best choice for achieving higher PCE. TDM (transition density matrix), DOS (density of states) analysis, and binding energies all were estimated at MPW1PW91/6-31G (d, p) level of DFT (density functional theory). All the architecture molecules show reduced band gap and high electron transfer rate due to the lowest reorganization energy (RE) of electron. The results show that there is greater contribution of acceptor and conjugated donor core towards the total absorption into the visible region of the spectrum. When tailored molecules D-1, D-2, D-3, and D-4 were blended with fullerene derivative polymer (PC₆₁BM), they give high values of voltage at zero current level (V_oc) compared to R.

Push or Pull Electrons: Acetoxy and Carbomethoxy-Substituted Isomerisms in Organic Solar Cell Acceptors

Isomerism is a major factor affecting the properties of materials. Herein, two isomeric acceptors based on acetoxy and methyl ester end group substituents, BTIC-OCOMe and BTIC-COOMe are reported. When blended with PBDB-TF, devices based on BTIC-OCOMe achieve an inferior (8.32%) power conversion efficiency (PCE) while the BTIC-COOMe material has a superior PCE of 13.25%. We investigated the reasons why these two devices, which differ only in the isomeric substituents on the terminal site, have such a large difference in photovoltaic performance. Our investigation conducted theoretical calculations and examined UV-vis absorption, energy levels, exciton dissociation and bimolecular recombination, mobilities tests, photoluminescence, and packing modes. It is found that the energy levels of the materials are fine-tuned, the absorption spectra are adjusted, and the energy loss is regulated. Our studies explored the reasons for the properties of materials differing, and the acetoxy and carbomethoxy substitutions provided some useful information concerning high-performance acceptor materials.

An N-type Naphthalene Diimide Ionene Polymer as Cathode Interlayer for Organic Solar Cells

Polymer solar cells (PSCs) based on non-fullerene acceptors have the advantages of synthetic versatility, strong absorption ability, and high thermal stability. These characteristics result in impressive power conversion efficiency values, but to further push both the performance and the stability of PSCs, the insertion of appropriate interlayers in the device structure remains mandatory. Herein, a naphthalene diimide-based cathode interlayer (NDI-OH) is synthesized with a facile three-step reaction and used as a cathode interlayer for fullerene and non-fullerene PSCs. This cationic polyelectrolyte exhibited good solubility in alcohol solvents, transparency in the visible range, self-doping behavior, and good film forming ability. All these characteristics allowed the increase in the devices’ power conversion efficiencies (PCE) both for fullerene and non-fullerene-based PSCs. The successful results make NDI-OH a promising cathode interlayer to apply in PSCs.