All-polymer solar cells (all-PSCs) consisting of polymer donors (P Ds) and polymer acceptors (P As) have drawn tremendous research interest in recent years. It is due to not only their tunable ...optical, electrochemical, and structural properties, but also many superior features that are not readily available in conventional polymer–fullerene solar cells (fullerene-PSCs) including long-term stability, synthetic accessibility, and excellent film-forming properties suitable for large-scale manufacturing. Recent breakthroughs in material design and device engineering have driven the power conversion efficiencies (PCEs) of all-PSCs exceeding 11%, which is comparable to the performance of fullerene-PSCs. Furthermore, outstanding mechanical durability and stretchability have been reported for all-PSCs, which make them stand out from the other small molecule-based PSCs as a promising power supplier for wearable electronic devices. This review provides a comprehensive overview of the important work in all-PSCs, in which pertinent examples are deliberately chosen. First, we describe the key components that enabled the recent progresses of all-PSCs including rational design rules for efficient P Ds and P As, blend morphology control, and light harvesting engineering. We also review the recent work on the understanding of the stability of all-PSCs under various external conditions, which highlights the importance of all-PSCs for future implementation and commercialization. Finally, because all-PSCs have not yet achieved their full potential and are still undergoing rapid development, we offer our views on the current challenges and future prospects.
All-polymer solar cells (all-PSCs), consisting of conjugated polymers as both electron donor (PD) and acceptor (PA), have recently attracted great attention. Remarkable progress has been achieved ...during the past few years, with power conversion efficiencies (PCEs) now approaching 8%. In this Account, we first discuss the major advantages of all-PSCs over fullerene–polymer solar cells (fullerene-PSCs): (i) high light absorption and chemical tunability of PA, which affords simultaneous enhancement of both the short-circuit current density (J SC) and the open-circuit voltage (V OC), and (ii) superior long-term stability (in particular, thermal and mechanical stability) of all-PSCs due to entangled long PA chains. In the second part of this Account, we discuss the device operation mechanism of all-PSCs and recognize the major challenges that need to be addressed in optimizing the performance of all-PSCs. The major difference between all-PSCs and fullerene-PSCs originates from the molecular structures and interactions, i.e., the electron transport ability in all-PSCs is significantly affected by the packing geometry of two-dimensional PA chains relative to the electrodes (e.g., face-on or edge-on orientation), whereas spherically shaped fullerene acceptors can facilitate isotropic electron transport properties in fullerene-PSCs. Moreover, the crystalline packing structures of PD and PA at the PD–PA interface greatly affect their free charge carrier generation efficiencies. The design of PA polymers (e.g., main backbone, side chain, and molecular weight) should therefore take account of optimizing three major aspects in all-PSCs: (1) the electron transport ability of PA, (2) the molecular packing structure and orientation of PA, and (3) the blend morphology. First, control of the backbone and side-chain structures, as well as the molecular weight, is critical for generating strong intermolecular assembly of PA and its network, thus enabling high electron transport ability of PA comparable to that of fullerenes. Second, the molecular orientation of anisotropically structured PA should be favorably controlled in order to achieve efficient charge transport as well as charge transfer at the PD–PA interface. For instance, face-to-face stacking between PD and PA at the interface is desired for efficient free charge carrier generation because misoriented chains often cause an additional energy barrier for overcoming the binding energy of the charge transfer state. Third, large-scale phase separation often occurs in all-PSCs because of the significantly reduced entropic contribution by two macromolecular chains of PD and PA that energetically disfavors mixing. In this Account, we review the recent progress toward overcoming each recognized challenge and intend to provide guidelines for the future design of PA. We believe that by optimization of the parameters discussed above the PCE values of all-PSCs will surpass the 10% level in the near future and that all-PSCs are promising candidates for the successful realization of flexible and portable power generators.
All-polymer solar cells have shown great potential as flexible and portable power generators. These devices should offer good mechanical endurance with high power-conversion efficiency for viability ...in commercial applications. In this work, we develop highly efficient and mechanically robust all-polymer solar cells that are based on the PBDTTTPD polymer donor and the P(NDI2HD-T) polymer acceptor. These systems exhibit high power-conversion efficiency of 6.64%. Also, the proposed all-polymer solar cells have even better performance than the control polymer-fullerene devices with phenyl-C61-butyric acid methyl ester (PCBM) as the electron acceptor (6.12%). More importantly, our all-polymer solar cells exhibit dramatically enhanced strength and flexibility compared with polymer/PCBM devices, with 60- and 470-fold improvements in elongation at break and toughness, respectively. The superior mechanical properties of all-polymer solar cells afford greater tolerance to severe deformations than conventional polymer-fullerene solar cells, making them much better candidates for applications in flexible and portable devices.
The use of lithium metal anodes in solid-state batteries has emerged as one of the most promising technologies for replacing conventional lithium-ion batteries
. Solid-state electrolytes are a key ...enabling technology for the safe operation of lithium metal batteries as they suppress the uncontrolled growth of lithium dendrites. However, the mechanical properties and electrochemical performance of current solid-state electrolytes do not meet the requirements for practical applications of lithium metal batteries. Here we report a class of elastomeric solid-state electrolytes with a three-dimensional interconnected plastic crystal phase. The elastomeric electrolytes show a combination of mechanical robustness, high ionic conductivity, low interfacial resistance and high lithium-ion transference number. The in situ-formed elastomer electrolyte on copper foils accommodates volume changes for prolonged lithium plating and stripping processes with a Coulombic efficiency of 100.0 per cent. Moreover, the elastomer electrolytes enable stable operation of the full cells under constrained conditions of a limited lithium source, a thin electrolyte and a high-loading LiNi
Mn
Co
O
cathode at a high voltage of 4.5 volts at ambient temperature, delivering a high specific energy exceeding 410 watt-hours per kilogram of electrode plus electrolyte. The elastomeric electrolyte system presents a powerful strategy for enabling stable operation of high-energy, solid-state lithium batteries.
Nonfullerene acceptors (NFAs), that are small-molecule acceptors (SMA) and polymer acceptors (PAs), have been extensively explored, which has yielded significant enhancements in the photovoltaic ...performance of polymer solar cells (PSCs). The mechanical robustness of the PSCs is of vital and equal importance to ensure long-term stability and enable their use as power-generators in flexible and stretchable electronics. Here, we report a comparative study of the mechanical properties of SMA-based, PA-based, and fullerene-based PSCs. We chose ITIC (SMA), P(NDI2OD-T2) (PA), and PCBM (fullerene) as three representative acceptor materials and blended them with the same polymer donor PTB7-Th. To understand the difference between the mechanical properties of SMA-based and PA-based PSCs, we control the number-average molecular weight (M n) of P(NDI2OD-T2) from 15 to 163 kg mol–1 in all-PSCs. The all-PSCs-based high-M n PAs exhibit significantly higher cohesion energy (4.03 J m–2) than SMA-PSCs (1.19 J m–2) and PCBM-PSCs (0.29 J m–2). Notably, the all-PSCs exhibit a high strain at fracture of 31.1%, which is 9- and 28-fold higher than those of SMA-PSCs and PCBM-PSCs, respectively. The superior mechanical robustness of all-PSCs is attributed to using a PA above the critical molecular weight (M c), which produces tie molecules and polymer entanglements that dissipate substantial mechanical strain energy with large plastic deformation. This work provides useful design guidelines for photovoltaic active materials in terms of the mechanical properties and highlights the importance of incorporating high-M n PAs above the M c for producing PSCs with excellent mechanical robustness and device performance.
Despite the recent breakthroughs of polymer solar cells (PSCs) exhibiting a power conversion efficiency of over 17%, toxic and hazardous organic solvents such as chloroform and chlorobenzene are ...still commonly used in their fabrication, which impedes the practical application of PSCs. Thus, the development of eco-friendly processing methods suitable for industrial-scale production is now considered an imperative research focus. This Review provides a roadmap for the design of efficient photoactive materials that are compatible with non-halogenated green solvents (e.g., xylenes, toluene, and tetrahydrofuran). We summarize the recent development of green processing solvents and the processing methods to match with the efficient photoactive materials used in non-fullerene solar cells. We further review progress in the use of more eco-friendly solvents ( i.e. , water or alcohol) for achieving truly sustainable and eco-friendly PSC fabrication. For example, the concept of water- or alcohol-dispersed nanoparticles made of conjugated materials is introduced. Also, recent important progress and strategies to develop water/alcohol-soluble photoactive materials that completely eliminate the use of conventional toxic solvents are discussed. Finally, we provide our perspectives on the challenges facing the current green processing methods and materials, such as large-area coating techniques and long-term stability. We believe this Review will inform the development of PSCs that are truly clean and renewable energy sources.
The energy level alignment of the perovskite and hole transporting materials (HTMs) is essential for increasing the open‐circuit voltage (Voc) and enhancing the performance of perovskite solar cells ...(PSCs). In this work, new sequentially fluorinated poly(triarylamine) polymers (PTAA, 1F‐PTAA, and 2F‐PTAA) with tuned highest occupied molecular orbital (HOMO) energy levels are developed and applied as HTMs into PSCs. The fluorination approach successfully leads to stepwise downshifting of the HOMO levels of PTAA derivatives, resulting in an obvious increase in the Voc and power conversion efficiency (PCE) of the PSCs. In particular, introduction of 1F‐PTAA polymer in (FAPbI3)0.85(MAPbBr3)0.15‐based mesoporous n‐i‐p structure PSCs achieves the high stabilized PCE of 21.2% at the maximum power point with improved Voc of 1.14 V. To elucidate the importance of the optimized degree of fluorination of PTAA polymers on the photovoltaic performances, the optical, electrical, photophysical properties, and doping behaviors of the fluorinated PTAA derivatives are investigated.
New polymeric hole transporting materials (HTMs) with downshifted highest occupied molecular orbital (HOMO) energy levels are developed by sequentially introducing electron‐withdrawing fluorine groups into triarylamine‐based polymers. High‐performance perovskite solar cells with these HTMs exhibit outstanding efficiency at maximum power point of 21.2% and high open‐circuit voltage of 1.14 V as a result of a deeper HOMO level and efficient charge extraction.
Recent advances in the power conversion efficiency (PCE) of organic solar cells (OSCs) have greatly enhanced their commercial viability. Considering the technical standards (e.g., mechanical ...robustness) required for wearable electronics, which are promising application platforms for OSCs, the development of fully stretchable OSCs (f‐SOSCs) should be accelerated. Here, a comprehensive overview of f‐SOSCs, which are aimed to reliably operate under various forms of mechanical stress, including bending and multidirectional stretching, is provided. First, the mechanical requirements of f‐SOSCs, in terms of tensile and cohesion/adhesion properties, are summarized along with the experimental methods to evaluate those properties. Second, essential studies to make each layer of f‐SOSCs stretchable and efficient are discussed, emphasizing strategies to simultaneously enhance the photovoltaic and mechanical properties of the active layer, ranging from material design to fabrication control. Key improvements to the other components/layers (i.e., substrate, electrodes, and interlayers) are also covered. Lastly, considering that f‐SOSC research is in its infancy, the current challenges and future prospects are explored.
A comprehensive overview of fully stretchable organic solar cells (f‐SOSCs), including essential studies to make each layer of an f‐SOSC stretchable and efficient is provided. Various strategies to simultaneously enhance the photovoltaic and mechanical properties of the active layer, ranging from material design to fabrication control, are emphasized.
Donor–acceptor random copolymers incorporating 1,3‐bis(thiophen‐2‐yl)‐5,7‐bis(2‐ethylhexyl)benzo1,2‐c:4,5‐c′dithiophene‐4,8‐dione (BDD) and ...4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo1,2‐b:4,5‐b′dithiophene (BDT‐Th) are developed. Nonfullerene solar cells introducing the random copolymer PBDB‐T73 (BDT‐Th:BDD=7:3) and 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno2,3‐d:2′,3′‐d′‐s‐indaceno1,2‐b:5,6‐b′dithiophene are found to exhibit efficiency of 11.14%, which is superior to that of the PBDB‐T alternating copolymer (10.02%). The PBDB‐T73 device exhibits high performance due to low bimolecular charge recombination and good charge transport balance even though none of the treatments that are usually necessary for improving crystalline properties of active layers are performed; in contrast, the PBDB‐T device requires thermal annealing in order to enhance the polymer's crystallinity and obtain improved fill factor and Jsc values. It is demonstrated that efficient charge transport occurs in the PBDB‐T73 blend despite relatively low crystallinity of the polymer. The percolating network structure of the large mixed phase in the PBDB‐T73 blend has an important role in its efficient charge transport. Moreover, due to the low‐temperature processability of PBDB‐T73, flexible PBDB‐T73 solar cell devices prepared on polyethylene terephthalate (PET) substrates exhibit high photovoltaic performance, 10.02%, whereas the efficiency of PBDB‐T‐based flexible devices (7.2%) is significantly lower due to damage to the active layer on indium tin oxide (ITO)/PET that results from thermal annealing.
Donor–acceptor‐type random copolymers are developed and nonfullerene polymer solar cells (PSCs) introducing the resulting polymer achieve a high efficiency of 11.14%. Furthermore, the corresponding flexible PSC using a random copolymer PBDB‐T73 shows a high efficiency of 10.02% due to low‐temperature processability of the polymer.
Mechanical properties of conducting polymers are an essential consideration in the design of flexible and stretchable electronics, but the guidelines for the material design having both high ...mechanical and electrical properties remain limited. Here we provide an important guideline for the design of mechanically robust, electroactive polymer thin films in terms of the molecular weight of the polymers. These studies based on a highly efficient, representative n-type conjugated polymer (P(NDI2OD-T2)) revealed a marked enhancement in mechanical properties across a narrow molecular weight range, highlighting the existence of a critical molecular weight that can be exploited to engineer films that balance processability and mechanical and electronic properties. We found the thin films formed from high molecular weight polymers (i.e., number-average molecular weight (M n) ∼ 163 kg mol–1) to exhibit superior mechanical compliance and robustness, with a 114-fold enhanced strain at fracture and a 2820-fold enhanced toughness, as compared to those of low molecular weight polymer films (M n = 15 kg mol–1). In particular, we observed a jump in the mechanical properties between the M n = 48 and 103 kg mol ‑1, yielding a 26-fold enhanced strain at fracture and a 160-fold enhanced toughness. The significant improvement of tensile properties indicates the presence of a critical molecular weight at which entangled polymer networks start to form, as supported by the analysis of the thermal and crystalline properties, specific viscosity, and microstructure. Our work provides useful guidelines for the design of conjugated polymers with recommendations for the best combinations of mechanical robustness and electrical performance for flexible and stretchable electronics.
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