The printing of large‐area organic solar cells (OSCs) has become a frontier for organic electronics and is also regarded as a critical step in their industrial applications. With the rapid progress ...in the field of OSCs, the highest power conversion efficiency (PCE) for small‐area devices is approaching 15%, whereas the PCE for large‐area devices has also surpassed 10% in a single cell with an area of ≈1 cm2. Here, the progress of this fast developing area is reviewed, mainly focusing on: 1) material requirements (materials that are able to form efficient thick active layer films for large‐area printing); 2) modular designs (effective designs that can suppress electrical, geometric, optical, and additional losses, leading to a reduction in the PCE of the devices, as a consequence of substrate area expansion); and 3) printing methods (various scalable fabrication techniques that are employed for large‐area fabrication, including knife coating, slot‐die coating, screen printing, inkjet printing, gravure printing, flexographic printing, pad printing, and brush coating). By combining thick‐film material systems with efficient modular designs exhibiting low‐efficiency losses and employing the right printing methods, the fabrication of large‐area OSCs will be successfully realized in the near future.
The rapid development in large‐area organic solar cells (OSCs) is reviewed. Materials requirements, modular designs, and printing methods for large‐area OSCs are discussed. By combining thick‐film material systems with efficient modular designs, and then by employing the right printing methods, the fabrication of large‐area OSCs will be successfully realized in the near future.
Ternary organic solar cells are promising candidates for bulk heterojunction solar cells; however, improving the power conversion efficiency (PCE) is quite challenging because the ternary system is ...complicated on phase separation behavior. In this study, a ternary organic solar cell (OSC) with two donors, including one polymer (PTB7-Th), one small molecule (p-DTS(FBTTH2)2), and one acceptor (PC71BM), is fabricated. We propose the two donors in the ternary blend forms an alloy. A notable averaged PCE of 10.5% for ternary OSC is obtained due to the improvement of the fill factor (FF) and the short-circuit current density (J sc), and the open-circuit voltage (V oc) does not pin to the smaller V oc of the corresponding binary blends. A highly ordered face-on orientation of polymer molecules is obtained due to the formation of an alloy structure, which facilitates the enhancement of charge separation and transport and the reduction of charge recombination. This work indicates that a high crystallinity and the face-on orientation of polymers could be obtained by forming alloy with two miscible donors, thus paving a way to largely enhance the PCE of OSCs by using the ternary blend strategy.
Organic solar cells (OSCs) with nonfullerene acceptors (NFAs) exhibit efficient charge generation under small interfacial energy offsets, leading to over 18 % efficiency for the single‐junction ...devices based on the state‐of‐the‐art NFA of Y6. Herein, to reveal the underlying charge generation mechanisms, we have investigated the exciton binding energy (Eb) in Y6 by a joint theoretical and experimental study. The results show that owing to strong charge polarization effects, Y6 has remarkable small Eb of −0.11–0.15 eV, which is even lower than perovskites in many cases. Moreover, it is peculiar that the photoluminescence is enhanced with temperature, and the energy barrier for separating excitons into charges is evidently lower than the thermal energy according to the temperature dependence of photoluminescence, manifesting direct photogeneration of charge carriers enabled by weak Eb in Y6. Thus, charge generation in NFA‐based OSCs shows little dependence on interfacial driving forces.
Direct photogeneration of free charge carriers enabled by remarkably low exciton binding energies is demonstrated in the state‐of‐the‐art nonfullerene acceptor of Y6 by a joint experimental and theoretical study. This results in efficient charge generation under small interfacial energy offsets in the high‐efficiency nonfullerene organic solar cells.
Reducing the driving force of exciton dissociation into charge-transfer states is one effective solution to minimize energy loss and thus to improve power conversion efficiencies for organic solar ...cells. Traditionally, the driving force should be larger than 0.3 eV to achieve efficient exciton dissociation. Recent experiments have shown that excitons can be effectively dissociated, whereas the energy offsets between donor and acceptor are extremely small, but the mechanisms are not understood yet. Here, we use system-optimized long-range corrected functional with solid-state electronic polarization to investigate exciton binding energies of 14 typical nonfullerene small molecule acceptors in organic solar cells. The results point to that the driving forces for dissociation of the acceptor excitons into charge-transfer states are linearly correlated to the exciton binding energies. The smaller the exciton binding energy, the lower driving force required. Moreover, primarily owing to the largest dielectric constants, IDT- or IDTT-based fused-ring acceptors have the smallest exciton binding energies with respect to other acceptors, i.e., DPP-, PDI-, and BFI-based systems. The influence of conjugation lengths, strengths of electron-donating and withdrawing units, and molecular volumes on the dielectric constants are analyzed in detail. Our work rationalizes the experimental observations and would be helpful for designing active materials to reduce energy loss for organic solar cells.
The variation of the vertical component distribution can significantly influence the photovoltaic performance of organic solar cells (OSCs), mainly due to its impact on exciton dissociation and ...charge‐carrier transport and recombination. Herein, binary devices are fabricated via sequential deposition (SD) of D18 and L8‐BO materials in a two‐step process. Upon independently regulating the spin‐coating speeds of each layer deposition, the optimal SD device shows a record power conversion efficiency (PCE) of 19.05% for binary single‐junction OSCs, much higher than that of the corresponding blend casting (BC) device (18.14%). Impressively, this strategy presents excellent universality in boosting the photovoltaic performance of SD devices, exemplified by several nonfullerene acceptor systems. The mechanism studies reveal that the SD device with preferred vertical components distribution possesses high crystallinity, efficient exciton splitting, low energy loss, and balanced charge transport, resulting in all‐around enhancement of photovoltaic performances. This work provides a valuable approach for high‐efficiency OSCs, shedding light on understanding the relationship between photovoltaic performance and vertical component distribution.
High‐performance binary photovoltaic devices based on D18 and L8‐BO are constructed via manipulating the vertical component distribution in a sequential deposition (SD) process. After tuning the spin‐coating speeds of film deposition, the optimal SD device affords a record power conversion efficiency of 19.05% (certified, 18.9%) for binary single‐junction organic solar cells, much higher than that of the corresponding blend casting device (18.14%).
Fine count two‐ply yarn supercapacitors are constructed from carbon nanotube yarns and polyaniline nanowires. The thread‐like supercapacitor possess excellent electrochemical capacity and are very ...strong and flexible. When being woven or knitted into wearable electronic devices, alone or in combination with conventional textile yarns, the two‐ply yarn supercapacitors can be flexed and stretched repeatedly without significant loss of capacitance.
Linear (fiber or yarn) supercapacitors have demonstrated remarkable cyclic electrochemical performance as power source for wearable electronic textiles. The challenges are, first, to scale up the ...linear supercapacitors to a length that is suitable for textile manufacturing while their electrochemical performance is maintained or preferably further improved and, second, to develop practical, continuous production technology for these linear supercapacitors. Here, we present a core/sheath structured carbon nanotube yarn architecture and a method for one-step continuous spinning of the core/sheath yarn that can be made into long linear supercapacitors. In the core/sheath structured yarn, the carbon nanotubes form a thin surface layer around a highly conductive metal filament core, which serves as current collector so that charges produced on the active materials along the length of the supercapacitor are transported efficiently, resulting in significant improvement in electrochemical performance and scale up of the supercapacitor length. The long, strong, and flexible threadlike supercapacitor is suitable for production of large-size fabrics for wearable electronic applications.
Polymer/small molecule/fullerene based ternary solar cells have made great progress and have attracted considerable attention in recent years. The addition of small molecules can effectively ...compensate for the disadvantages of polymer solar cells, such as increasing the light‐harvesting ability, providing cascade energy levels, and tuning the morphology. Thus, polymer/small molecule/fullerene based ternary solar cells are promising candidates to obtain further improvements in photovoltaic performance for organic solar cells. This article summarizes the developments of ternary solar cells with small molecules as third components, and represents the possible photo‐physics process in the ternary blends. In addition, the challenges and perspectives for ternary solar cells are discussed.
Ternary solar cells have made great progress in recent years. The state of polymer/small molecule/PCBM (fullerene acceptor) ternary systems is reviewed, with a focus on 1) the functions of small molecules, such as improving the light‐harvesting ability, 2) the photo‐physics process occurring in ternary systems, and 3) the influence of the small molecule on the crystallinity of the host polymer and the morphology of the active layer.
Vertically aligned conducting polymer nanowire arrays have great potential applications in supercapacitor electrode materials. In this paper, we report a facial one-step template-free approach to ...synthesize large arrays of vertically aligned polyaniline (PANI) nanowires on various conducting substrates by using a galvanostatic current method. The as-prepared large arrays of PANI nanowires had very narrow diameters and were oriented perpendicular to the substrate, which was a benefit to the ion diffusion when being used as the supercapacitor electrode. The highest specific capacitance of PANI nanowire arrays was measured as 950 F·g−1 and kept as high as 780 F·g−1 at a large charge−discharge current density (40 A·g−1). Furthermore, the capacitances in several different electrolytes, including HClO4, lithium bis(trifluoromethane sulfonyl) (LiTFSI) aqueous solution and nonsolvent electrolyte ionic liquid, were investigated. The results indicated that the orientation of nanostructures could dramatically enhance the electrochemical performance of functional nanomaterials.
Broadening the optical absorption of organic photovoltaic (OPV) materials by enhancing the intramolecular push-pull effect is a general and effective method to improve the power conversion ...efficiencies of OPV cells. However, in terms of the electron acceptors, the most common molecular design strategy of halogenation usually results in down-shifted molecular energy levels, thereby leading to decreased open-circuit voltages in the devices. Herein, we report a chlorinated non-fullerene acceptor, which exhibits an extended optical absorption and meanwhile displays a higher voltage than its fluorinated counterpart in the devices. This unexpected phenomenon can be ascribed to the reduced non-radiative energy loss (0.206 eV). Due to the simultaneously improved short-circuit current density and open-circuit voltage, a high efficiency of 16.5% is achieved. This study demonstrates that finely tuning the OPV materials to reduce the bandgap-voltage offset has great potential for boosting the efficiency.
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