Active Layer Material Research Articles

Semicrystalline Cathode Interlayer Based on Morphology Control Additives Using Nonconjugated Small‐Molecule Zwitterions for Efficient Organic Solar Cells

The cathode interlayer (CIL) has significant impact on the performance of organic solar cells (OSCs), including the abilities to align energy levels, form ohmic contacts between the active layer and the electrode, and promote the electron extraction and transportation. However, the developments of CILs are still far behind the rapid explosion of active layer materials, especially for these nonfullerene acceptors (NFAs). This research provides a brand‐new CIL optimization approach by applying the nonconjugated small‐molecule zwitterion (NSMZ) as the morphology control additives (MCAs). Two novel NSMZs, 4‐(1‐methyl piperidin‐1‐ium‐1‐yl)butane‐1‐sulfonate (MPBS) and 3‐(1‐methylpiperidin‐1‐ium‐1‐yl)‐propane‐1‐sulfonate, are developed as MCAs for the improvements of short‐circuit current, fill factor, and power conversion efficiency (PCE) in various solar cell systems of the classic active layers and CILs. The interaction mechanism is systematically investigated. With the reduced energy barrier and suppressed electron recombination, a champion PCE of 18.65% on binary NFA–OSCs is achieved by incorporating the zwitterion of MPBS into the cathode interlayer as the additive, which is among the highest efficiency of the reported binary OSCs. The application of the zwitterion as MCAs for the cathode interlayer opens a novel avenue for highly efficient OSCs.

The nature of excitons in PPDT2FBT:PCBM solar cells: Role played by PCBM

In organic semiconductor-based bulk heterojunction solar cells, the presence of an acceptor increases the formation of charge-transfer (CT) excitons, thereby leading to higher exciton dissociation probabilities. In this work we used steady-state electroabsorption (EA) measurements to probe the change in the nature of excitons as the blend composition of the solar cell active layer material was varied. We investigated blends of poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-[1,2,5]thiadiazole)] (PPDT2FBT) and (6,6)-phenyl C71 butyric acid methyl ester (PCBM). Analysis of the EA spectra showed that in the presence of a fullerene-based acceptor, like PCBM, CT characteristics of the excitons were modified, though no new CT signature was observed in the blend. Enhancement in the CT characteristics in the blend was reflected in photoluminescence (PL) measurements of the blends, where PL quenching of ∼63% was observed for 1% PCBM. The quenching reaches saturation at about 20% PCBM. However, efficiency of the device increased with a PCBM percentage beyond 20%. Maximum efficiency was obtained for the blend with 50% PCBM, among the blend compositions studied in this work, indicating the optimum concentration of PCBM for best power conversion efficiency to be around that value. When we compared the experimental results with simulations, the variation of the device efficiency with PCBM percentage was shown to arise from multiple factors, such as an increase in the polarizability and dipole moment of excitons, and the efficiency of the carrier collection from the bulk of the active layer.

Synergistic high efficiency and low energy loss of all-small-molecule organic solar cells based on benzotriazole-based π-bridge unit

Reducing energy loss (Vloss) is one of the most crucial challenges in organic photovoltaic cells. The Vloss, determined by the differences between the optical band gap (Eg) of the active layer material and the open-circuit voltage (Voc) of the device, is generally alleviated by lowering the energy difference between the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) level of the donor (D) and acceptor (A). In this work, we synthesized two A-π-D-π-A-type small-molecule donors (SMDs) SM-benzotriazole (BTz)-1 and SM-BTz-2 by introducing a BTz π-bridge unit and terminal regulation. The BTz π-bridge unit significantly lowers the HOMO energy level of SMDs, resulting in high Voc and high mobility, achieving a balance of low energy loss (<0.5 eV) and high efficiency. Ultimately, the organic solar cells based on SM-BTz-2 as the donor and Y6 as the acceptor obtain a high Voc of 0.91 V, Jsc of 22.8 mA cm−2, fill factor of 68%, and power conversion efficiency (PCE) of 14.12%, which is one of the highest efficiencies based on the SMDs with triazole π-bridges to date. What’s more, the BTz π-bridge unit is a potential unit that can improve mobility and reduce energy loss.

Investigation on the parameter dependency of the perforation process of graphite based lithium-ion battery electrodes using ultrashort laser pulses

Perforation of lithium-ion battery electrodes has recently become an increasing interest in science and industry. Perforated electrodes have shown improved electrochemical properties compared to conventional, nonperforated electrodes. It has been demonstrated that through perforation, the fast-charging capability and the lifetime of these batteries can be significantly improved. The electrodes for lithium-ion batteries consist of a copper foil onto which the electrode material is applied as a porous layer. This layer is mainly composed of active material particles, which are bound together by a binder phase. Here, synthetic graphite was used as an active material. Up to now, it has been shown that an advantageous and precise perforation geometry can be produced by ultrashort laser pulse ablation. Since the ablation volumes during perforation of the porous electrode material with ultrashort laser pulses are unusually high compared to solids, this work investigates the parameter dependency on the ablation mechanisms in detail. For this purpose, in particular, single-pulse ablation was investigated with respect to the ablation thresholds at different pulse durations. The pulse durations were varied over a large range from 400 fs to 20 ps. By varying the number of pulses per perforation up to 50 and the single-pulse energy up to 45 μJ, it could be shown that a homogeneous ablation down to the conductor foil through the 63 μm thick active material layer can be achieved.

Mechanism Analysis and Highly Scaled Aluminum Nitride‐Based Self‐Rectifying Memristors

AbstractStorage‐class memory and advanced neuromorphic‐related applications place an urgent requirement on large‐scale, highly compacted memristor array. However, crosstalk issue constrains the addressing accuracy and effective data scale of current array‐level memristor, which is detrimental to the industrial realization. Herein, scalability and physical processes of Al/AlN/W self‐rectifying memristor are investigated. The devices exhibit improved rectification ratio from 94 to 2600, switching ratio from 286 to 6099, higher uniformity, reliability, and nonvolatility by scaling the size from 10 to 5 µm. The application of aluminum nitride as active layer material not only makes the electrical properties more sensitive to the external electric field, but also dominates the switching process by constructing nitrogen vacancy conducting filaments, as demonstrated by a combination of scalability and mechanistic analysis. The high‐scaled AlN‐based self‐rectifying memristor exhibits a maximum effective array size of N = 14 372, which is 53 times enhancement compared to 10 µm size cells. The Al/AlN/W self‐rectifying memristor is confirmed to have a strong ability to suppress sneak currents and has the potential to serve large‐scale array‐level applications.

Ambipolar Organic Field‐Effect Transistors and Complementary Circuits Based on Single Crystals with Alcohol Treatment

AbstractAmbipolar organic field‐effect transistors (OFETs) are promising candidates for compact organic complementary circuits. High and balanced ambipolar mobilities that facilitate high operation speed and simplifying layout designs, as well as symmetric electrodes that minimize fabrication complexity are critical integrities for state‐of‐art ambipolar OFETs. Organic single crystals with intrinsic ambipolar characteristics are ideal active layer materials because of the high molecular ordering and low density of defects, whereas the generally low electron mobility hindered their further implantation. In this work, the highly crystallized 6,13‐bis(triisopropylsilylethynyl) pentacene single crystals are employed and successfully unveiled the intrinsic high electron mobility by a facile alcohol treatment approach. The resulting ambipolar OFETs showed averaged hole and electron mobilities both higher than 1 cm2 V−1 s−1 by a single type of metal electrode. The presented ambipolar OFETs not only improved the static and dynamic performance of ambipolar OFET‐based complementary inverters and ring oscillators by showing a high voltage gain of 186 and a short stage delay time of 0.7 ms, but they also allowed one logic gate to show two logic functions and potentially benefit the design and functionalities of future OFET‐based complementary circuits as well.

MEMS based energy scavenger with interdigitated electrodes

MEMS-based energy scavengers have attracted industries and researchers as promising solutions to the energy crises which will certainly affect the present and future generations due to increased population and/or pollution. The capability of miniaturized energy scavengers to generate usable energy from ambient vibrations makes them a special and effective alternative to clean energy sources that can be used in many applications like point of care testing devices, and self-power micro-systems, low duty cycle applications, etc. MEMS-based energy scavenger using Zinc Oxide (ZnO) piezoelectric material for active layer is proposed here which can be used to drive the low power applications. The spin coating method with optimized speed was effectively used for ZnO deposition. Aluminum foil-based Interdigitated Electrodes (IDE) were used to ensure good flexibility, no internal defects, and crack-free movement during vibrations. The low-cost, easily available, flexible Polyethylene Terephthalate (PET) substrate used in the passive layer makes the scavenger suitable for energy harvesting from vibrations of many natural surface structures which are not flat such as clothes, human bodies, household equipment, industrial machines, etc. The MEMS-based Energy Scavenger with Interdigitated Electrodes (MEMS-ES-IDE) generated 3 V open-circuit voltage (OCV) at 60 Hz resonant frequency. Based on the obtained values of OCV, it was confirmed that the fabricated MEMS-ES-IDE would be used in a variety of low-duty cycle applications.

The use of machine learning, density functional theory, and molecular dynamics simulations for the designing and screening of efficient small molecule donors for organic solar cells

AbstractIndeed, a proper understanding of materials is necessary to get the full benefit from them. For this purpose, multiscale computational modeling is the ultimate need. For machine learning analysis, data is collected from the literature. Machine learning analysis is performed using molecular descriptors as independent parameters and power conversion efficiency (PCE) as dependent property. Various machine learning models are tried. The support vector machine (SVM) model has outperformed others. New donor materials that are small molecules are designed using both well‐known and new building blocks. Their PCE is predicted using a SVM model. The top 10 small molecule donors are further studied using density functional theory calculations. Their electronic behavior is studied. Reorganization energy, exciton binding energy and transfer integral are also calculated. Finally, the best three small molecule donors are selected for molecular dynamics simulations. Molecular packing and mixing of active layer materials is studied using radial distribution function. Our proposed framework has the ability to design potential donor materials in short time with marginal computational cost.

AIE Molecules UV‐Filtering Effect Improves the Photostability of Organic Solar Cells

AbstractDue to the poor stability of organic solar cells (OSCs), especially ultraviolet light (UV) stability, they are not yet up to the standard for commercial applications. Inverted devices based on the ZnO electron transport layer (ETL) are relatively thermal‐ and air‐stable, while their UV light stability is poor. Moreover, the active layer materials undergo severe degradation under UV light, which also causes the degradation of the device. Here, aggregation‐induced emission (AIE) molecules as an optical barrier layer are coated between ZnO‐ETL and active layer to fabricate efficient OSCs with excellent UV photostability. AIE molecules can avoid direct photodegradation of the active layer materials by absorbing UV light. At the same time, they can passivate the oxygen defects on the ZnO surface and prevent photocatalytic degradation of the active layer materials. Therefore, the ZnO/TPIZ‐based devices maintain 84% of the original power conversion efficiency (PCE) with continuous irradiation by 5 mW cm–2 UV light (365 nm) for 1500 h, and similarly T80 for more than 700 h under 20 mW cm–2 UV light exposure. Moreover, the ZnO/TPIZ‐based devices also preserve excellent thermal stability accompanying the upgrading of PCE.

(Digital Presentation) Fabrication of Conductive Carbon Composite Films for Freestanding Lib Anodes Using Cellulose Nanofiber Binder

Fig.1 Cycle performance and Coulomb efficiency of graphite/CNT/CNF composite electrodes Introduction Currently, lithium-ion batteries (LIBs) have been the primary power source for electric vehicles and portable devices. LIBs consist of anodes (e.g. graphite), cathodes (e.g. LiCoO2: LCO), and electrolytes,[1] and are dis-/ charged as Li+ de-/ intercalate between the electrodes. Since LIBs require expensive fluorinated polymer as binders (e.g. poly (vinylidene fluoride): PVDF) and a volatile and toxic organic solvent such as N-methyl pyrrolidone (NMP), cheaper and easier-to-handle materials are necessary. Furthermore, the metal substrates (Cu, Al foil, etc.) as the current collectors are heavy and reduce the weight energy density of electrodes. Therefore, providing alternatives to the conventional components of LIB electrodes is a key challenge. Developing functional nanocomposites using sustainable natural resources is one of the most importance strategies.[2] Conductive thin films of cellulose nanofibers (CNFs) combined with carbon nanotubes (CNTs) have been reported as novel carbon composites.[3] Environmentally friendly and only carbonaceous electrodes without PVDF and organic solvents, and graphite are normally used for anodes. As an allotrope of graphite, CNTs have been approved to be a suitable anode material due to their unique structure (one-dimensional cylindrical tubule of graphite sheet), high conductivity (106 Sm-1 at 300 K), low density, high rigidity (Young’s modulus 1 TPa), and high tensile strength (up to 60 GPa).[4] In this study, the free-standing carbon composite anodes were successfully fabricated by using ultrasonication of CNF/ CNT or graphite mixture and vacuum filtering. Graphite slurry as the active material layer was dispersed in DI-water as the solvent containing CNF binder. This composite film has a dual-layer structure consisting of graphite/CNF active materials layer and CNT/CNF layer; here, the CNT/CNF layer with a thickness of about 10 μm is utilized as a current collector replacing the conventional metal substrate. These fabricated electrodes were evaluated by structural evaluation and dis-/ charge measurements. Experimental method CNF gel (2 wt%, Rheocrysta, DKS Co. Ltd.) and functionalized (carboxylic acid) multi-walled CNT (f-MWCNT, Sigma-Aldrich) were suspended in DI-water and sonicated for 2 h. Synthetic graphite was dispersed in DI-water with 5 wt% CNF and 10 wt% Carbon Black (CB) as a conductive material and sonicated for 30 min. Nanocomposite dual-layer films were formed by vacuum-filtering the dispersion using PVDF (pore size: 0.1 μm) membrane filters. These films were characterized by scanning electron microscope (SEM), atomic force microscope (AFM), and Raman spectroscopy. The conductivity was measured by four probe method. The electrochemical properties of the free-standing electrode were measured using coin cells at room temperature. The coin cells were assembled in an argon-filled glovebox using Li as a counter electrode, glass fiber filter as a separator, and 1 M LiPF6 in a 1:1 (volume) mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) as the electrolyte. Charge-discharge characteristics were recorded from 0.01 to 3 V at charging speeds of 0.1 – 2 C. The electrochemical impedance spectra (EIS) were measured in the frequency range from 100 mHz to 100 kHz with a potential perturbation at 5 mV. Results CNF combined with CNT constructs a robust conductive fibrous network, and CNT linked with graphite builds electronic conductive paths to improve the electronic conductivity. Specific capacities of the electrode were 44 mAhg-1 at 2 C and 272 mAhg-1 at 0.5 C, respectively (Fig.1). The discharge capacity of the first cycle was 363 mAhg-1 at 0.1 C. After 125 cycles, the discharge capacity was 255 mAhg-1 at 0.5 C. The ratio of the charge and discharge capacities (Coulombic efficiency) suggests that the charge-discharge behavior is stable in the cycle measurement, indicating that the irreversible capacity was small. Other information obtained by cyclic voltammetry (CV), and EIS measurement and further results will be shown in the presentation. In summary, we successfully fabricated the graphite/CNT/CNF composite film as environmentally friendly and lightweight anodes for the first time. The present results indicate that graphite/CNT/CNF composite film is a good candidate of flexible free-standing anodes. This research focused on CNFs as a promising alternative to conventional battery materials, and CNFs were successfully used to fabricate electrodes without using expensive PVDF binders and toxic organic solvents. Moreover, the gravimetric energy density was improved by replacing the conventional heavy Cu foil with a lightweight and thin composite film of CNT/CNF.

Graphene as a hole transport layer for enhanced performance of P3HT: PCBM bulk heterojunction organic solar cell: a numerical simulation study

As sustainable and green energy technologies advance, academic and industrial researchers have been more interested in organic solar cells. Organic solar cells have some key advantages, such as lightweight, flexibility and cheapness that make them an ideal choice as an alternative to other types of solar cells. Bulk heterojunction solar cells combine the advantages of easier fabrication and higher conversion efficiency, making them the best structure currently. In this work P3HT: PCBM is used as the active layer material. PDINO and PFN-Br are used as the electron transport layers in this work. Graphene, which is taken as the hole transport layer in this work, is a unique material for future applications in organic photovoltaics due to its remarkable optical properties and excellent electron/hole transport properties. Corresponding to two different electron transport layers two different device configurations are studied in the work. Bulk hetero-junction organic solar cell simulation study is done using the solar cell capacitance simulator (SCAPS1D). The thickness, electron and hole mobilities, and defect density of the active layer are varied for each device configuration, and their effect on device output performance is analysed. A comparative study of device performance between the different configurations has been done.

Research progress of large-area organic solar cells

<p indent="0mm">In recent years, organic solar cells (OSCs) have been developed rapidly, and their power conversion efficiencies (PCEs) of small-area OSCs have exceeded 19%. However, the performance of large-area devices lags far behind the development of the small-area ones. In-depth research on the major challenges of large-area organic photovoltaic devices and the development of large-area printing technologies is of great significance for promoting the industrial application of organic solar cells. Compared with small-area devices, the film thickness tolerance of the active layer, the sheet resistance of the transparent electrode, and the processing method should be mainly concentrated. Although the preparation of the large-area and stable OSCs has made significant progress and how to fabricate efficient, stable, rigid/flexible and large-area solar cells still remains a great challenge. In this review, focused on rigid and flexible substrates of large-area solar cells, we briefly summarized the new active layer materials, coating process, cathode/anode materials, electrode materials, <italic>etc</italic>. Considering the current trend, we believe the high-efficiency large-area OSCs in the laboratory would very soon lead to the production of highly efficient large-scale organic devices on an industrial scale.

Modulating the nanoscale morphology on carboxylate-pyrazine containing terpolymer toward 17.8% efficiency organic solar cells with enhanced thermal stability

It had been commonly accepted in the organic photovoltaic (OPV) community that subtle variations in the molecular structure of active layer materials would cause profound impacts on their aggregating structure and blend morphology and therefore the performance of such polymer solar cells (PSCs). Herein, we employed an electron-deficient building block 3,6-dithiophenyl-2-carboxylate pyrazine (DTCPz) for constructing one series of promising donor terpolymers of PMZ1, PMZ2, and PMZ3, respectively, gaining their relatively lower-lying highest occupied molecular orbital (HOMO) energy levels, more closed π-π stacking and enhanced crystallinity in thin films, and lower miscibility with acceptor Y6, in comparison with their parent polymer counterpart (namely PM6). Reaching DTCPz moieties up to 20% (mol/mol%) in its terpolymer composition, the resulting polymer (PMZ2) achieved more favorable phase separation with improved exciton dissociation, and charge transport and extraction. As a result, an outstanding fill factor of 77.2% and a promising power conversion efficiency of 17.8 % was achieved. Moreover, the corresponding device shows better thermal stability over the PM6-based one. This work suggests a facile method for significantly improving the thin film morphology of the active-layer materials via fine-tuning the chemical structure of electron-deficient units on the backbone of the wide bandgap donor polymer, therefore achieving enhanced photovoltaic performance and thermal stability for practical applications.

Driftfusion: an open source code for simulating ordered semiconductor devices with mixed ionic-electronic conducting materials in one dimension

The recent emergence of lead-halide perovskites as active layer materials for thin film semiconductor devices including solar cells, light emitting diodes, and memristors has motivated the development of several new drift-diffusion models that include the effects of both electronic and mobile ionic charge carriers. In this work we introduce Driftfusion, a versatile simulation tool built for modelling one-dimensional ordered semiconductor devices with mixed ionic-electronic conducting layers. Driftfusion enables users to model devices with multiple, distinct, material layers using up to four charge carrier species: electrons and holes plus up to two ionic species. The time-dependent carrier continuity equations are coupled to Poisson’s equation enabling transient optoelectronic device measurement protocols to be simulated. In addition to material and device-wide properties, users have direct access to adapt the physical models for carrier transport, generation and recombination. Furthermore, a discrete interlayer interface approach circumvents the requirement for boundary conditions at material interfaces and enables interface-specific properties to be introduced.

Anion-Doped Thickness-Insensitive Electron Transport Layer for Efficient Organic Solar Cells.

In organic solar cells, interfacial materials play essential roles in charge extraction, transportation, and collection. Currently, highly efficient and thickness-insensitive interfacial materials are urgently needed in printable large area module devices. Herein, water/alcohol-soluble conjugated polyelectrolyte PFNBT-Br, with medium bandgap based on benzothiadiazole, are doped by two alkali metal sodium salts, NaH2 PO2 , Na2 C2 O4 with different counter anions, to pursue high efficiency and thickness-insensitive electron-transport layers. Results show that the doping of electron-transport material can effectively promote the performance of the devices. Moreover, electron-transport layers doped by these salts with different counter anions show different behaviors in performances. Among which, the salt with oxalate anion C2 O4 2- (also named Ox2- ) shows much better device performance than the salt with hypophosphite anion (H2 PO2 - ), especially under the thick film condition (e.g., 50 nm). The greatly enhanced performances of interfacial material doped by Ox2- are due to reduced series resistance between the active layer material and the electrode, reduced dark-current, improved charge transport, and extraction efficiency, and decreased charge recombination for the devices at thick-film condition. These results demonstrated that n-doping could be a great potential strategy for making thickness-insensitive interfacial layers, besides, the performances can be further improved by carefully selecting salts.

Upscalable ultra thick rayon carbon felt based hybrid organic‐inorganic electrodes for high energy density supercapacitors

AbstractLow weight, small footprint, and high performances are essential requisites for the implementation of energy storage devices within consumer electronics. One way to achieve these goals is to increase the thickness of the active material layer. In this work, carbonized and graphitized rayon felt, a cellulose‐derived material, is used as a three‐dimensional current collector scaffold to enable the incorporation of large amount of active energy storage materials and ionic liquid‐based gel electrolyte in the supercapacitor devices. PEDOT:PSS, alone or in combination with active carbon, has been used as the active material. Three‐dimensional supercapacitors with high per unit area capacitance (more than 1.1 F/cm2) have been achieved owing to the loading of large amount of active material in the felt matrix. Areal energy density of more than 101 μWh/cm2 and areal power density of more than 5.9 mW/cm2 have been achieved for 0.8 V operating voltage at a current density of 1 mA/cm2. A nanographite material was found to be beneficial in reducing the internal serial resistance of the supercapacitor to lower than 1.7 Ω. Furthermore, it was shown that even after 2000 times cycling test, the devices could still retain its performance with at least 88% coulombic efficiency for all the devices. All the materials are readily available commercially, environmentally sustainable and the process can potentially be upscaled with industrial process.

Mass-Producible 2D Nanocomposite-Based Temperature-Independent All-Printed Relative Humidity Sensor.

Relative humidity sensors are widely studied under the categories of both environmental and biosensors owing to their vast reaching applications. The research on humidity sensors is mainly divided into two concentration areas including novel material development and novel device structure. Another approach focuses on the development of printed sensors with performance comparable to the sensors fabricated via conventional techniques. The major challenges in the research on relative humidity sensors include the range of detection, sensitivity (especially at lower %RH), transient response time, and dependence on temperature. Temperature dependence is one of the least studied parameters in relative humidity sensor development. In this work, relative humidity sensors were fabricated using all-printed approaches that are also compatible with mass production, resulting in low cost and easy development. Laser-induced graphene (LIG)-based printed electrodes were used as the transducers, while the 2D MoS2 and graphene nanocomposite was used as the active layer material with the built-in property of temperature independence. The exfoliation process of 2D MoS2 was based on wet grinding, while graphene for the active layer was obtained by scratching the graphene grown on the polyimide (PI) surface via laser ablation. The resulting sensors showed an excellent output response for a full range of 0%RH to 100%RH, having no dependence on the surrounding temperature, and excellent response and recovery times of 4 and 2 s, respectively. The developed sensors can be confidently employed for a wide range of humidity sensing applications where the temperature of the surrounding environment is not constant.

Using 3.0eV Large Bandgap Conjugated Polymer as Host Donor to Construct Ternary Semi-Transparent Polymer Solar Cells: Increased Average Visible Transmittance and Modified Color Temperature.

Although optical engineering strategy has been utilized to optimize average visible transmittance (AVT) of semi-transparent organic solar cells (ST-OSCs), judicious selection of active layer materials should be more direct and basic. Herein, an efficient ternary active layer is constructed with a wide bandgap (3.0eV) fluorescent polymer FC-S1 as host donor, a middle bandgap polymer PM6 as guest donor, and a narrow bandgap non-fullerene Y6-BO as acceptor. Using FC-S1 as the host donor can allow more visible photons to penetrate the device. In the absence of optical engineering, the ternary ST-OSC with FC-S1:PM6:Y6-BO=1:0.3:1.5 active layer of 30nm thickness displays a much higher AVT of 49.28% than that of 32.34% for a PM6:Y6-BO=1.3:1.5 based binary ST-OSC. The ternary ST-OSC provides a good power conversion efficiency of 6.01%, only slightly lower than 7.15% for the binary ST-OSC. The ternary ST-OSC also demonstrates a color rendering index (CRI) of 87 and a correlated color temperature (CCT) of 6916K, all better than CRI of 80 and CCT of 9022K for the binary ST-OSC. Moreover, the backbone of FC-S1 is mainly composed by fluorene and carbazole, two easily-accessible aromatic rings, which would meet low-cost concern of ST-OSCs.

Layer-by-layer and non-halogenated solvent processing of benzodithiophene-free simple polymer donors for organic solar cells

High performance and easy-synthesis benzodithiophene (BDT)-free simple active layer materials, green non-halogen solvent processing and convenient device fabrication with batch-to-bath stability are all crucial to realize the industrial production of organic solar cells (OSCs) in the future. In this work, we develop two BDT-free polymer donors, PBTz-TC and PBTz-TTC, for green halogen-free solvent and layer-by-layer (LBL) processed high performance OSCs. The strong molecular aggregation of BTz units helps to improve the crystallinity and film-forming properties of the polymers, while the introduction of ester groups assists in enhancing the solubility of conjugated polymers in both halogen and non-halogen solvents and down-shifting the energy levels. The synergistic implementation of LBL method and orthogonal solvents can significantly reduce the scouring effect during the sequential deposition process, which is conducive to construct planar heterojunction. Due to the more planar conformation, PBTz-TTC possesses more robust film-forming property with superior corrosion resistance to the upper-layer than PBTz-TC. While, PBTz-TC better balances the independent film formation and moderate miscibility with IT-4F acceptor to favor stronger interaction at the donor/acceptor interfaces. Consequently, PBTz-TC shows much better performance than PBTz-TTC in both bulk heterojunction and LBL devices, ascribed to the better energy alignment, more favorable morphology and more efficient charge dynamic process. Notably, when treated with halogen-free solvent, an outstanding power conversion efficiency (PCE) of 12.81% with improved stability is achieved for PBTz-TC/IT-4F-based LBL device, which is the highest value of non-halogenated solvent processed devices based on benzodithiophene-free simple polymer donors. These findings provide a guideline for rational design of the environmental friendly simple polymer donor materials for further acceleration of the industrial production of OSCs.

Simultaneously Decreasing the Bandgap and Voc Loss in Efficient Ternary Organic Solar Cells

AbstractTernary architecture is a promising strategy to further boost the performance of organic solar cells (OSCs). Reducing the bandgap of the active layer materials not only widens the absorption wavelength range and enhances the short‐circuit current (Jsc) of the OSC, but also decreases the open‐circuit voltage (Voc) of the device, leading to a trade‐off situation for the optimization of the material system. Herein, a small‐molecule donor BTID‐2F, featuring a narrower bandgap than that of PM6, is introduced into a PM6:Y6 based system. The redshift in external quantum efficiency indicates the narrower bandgap and better aggregation in the ternary blends than those of binary ones. Interestingly, lower energy disorder and energy loss are also attained for the ternary devices, leading to higher Voc. Furthermore, owing to the suppressed recombination and morphological optimization, a simultaneous enhancement in the Jsc and fill factor boosts the power conversion efficiency (PCE) of ternary OSC to 17.9% compared to 16.62% for the binary device. Likewise, replacing the acceptor with the L8‐BO molecule further improves the ternary PCE to 18.52%. This work indicates an emerging approach for fabricating high‐performance ternary OSCs with a decreased bandgap and increased Voc.