Acceptor Polymers Research Articles

Ternary All-Polymer Solar Cells with Efficiency up to 18.14% Employing a Two-Step Sequential Deposition.

Achieving a finely tuned active layer morphology with a suitable vertical phase to facilitate both charge generation and charge transport has long been the main goal for pursuing the highly efficient bulk heterojunction all-polymer solar cells (all-PSCs). Herein, a solution to address the above challenge via synergistically combining the ternary blend strategy and the layer-by-layer (LbL) procedure is proposed. By introducing a synthesized polymer acceptor (PA ), PY-Cl, with higher crystallinity into the designed host acceptor PY-SSe-V, vertical phase distribution and molecular ordering of the LbL-type ternary all-PSCs can be improved in comparison to the LbL-type PM6/PY-SSe-V binary all-PSCs. The formation of the superior bulk microstructure can not only promote charge transport and extraction properties but also reduce energetic disorder and non-radiative recombination loss, thus improving all three photovoltaic parameters simultaneously. Consequently, the PM6/(PY-SSe-V:PY-Cl) ternary all-PSCs show the best efficiency of 18.14%, which is among the highest values reported to date for all-PSCs. This work provides a facile and effective LbL-type ternary strategy for obtaining high-efficiency all-PSCs.

Layer‐by‐Layer Processed Efficient All‐Polymer Solar Cells Based on a Nonfused Polymerized Small Molecule Acceptor

AbstractThe development of polymer acceptors is of crucial importance for all‐polymer solar cells (all‐PSCs). However, the state‐of‐the‐art polymer acceptors are typically based on Y‐series small molecule acceptors. Their synthetic complexity and high synthesis cost remain a severe challenge for future practical application of organic photovoltaics. Herein, a novel non‐fused polymer acceptor named PDO is synthesized. The all‐PSC achieves a best power conversion efficiency of 9.68% in the layer‐by‐layer (LBL) processed device, which is much better than that (8.14%) of the conventional bulk‐heterojunction device. Comprehensive analysis on the electrical and morphological characterizations reveal that the improved device performance in the LBL‐processed device is originated from efficient exciton extraction and charge transport, suppresses charge recombination, improves molecular ordering, and optimizes active layer morphology. These results validate that the fabrication of all‐PSCs with non‐fused polymerized small molecule acceptors is a promising strategy to develop low‐cost and high‐performance all‐PSCs.

8.30% Efficiency P3HT-based all-polymer solar cells enabled by a miscible polymer acceptor with high energy levels and efficient electron transport

8.30% Efficiency P3HT-based all-polymer solar cells enabled by a miscible polymer acceptor with high energy levels and efficient electron transport

Intrinsic polarization-sensitive organic photodetector with self-assembled all-polymer heterojunction

Intrinsic polarization-sensitive photodetectors (IPPDs) have attracted considerable attention in recent years due to their simplicity in configuration, making them ideal candidates for compact and integrated polarization-sensitive sensing and imaging systems. Photoactive films with intrinsic optical anisotropy are necessary for IPPDs. This study reports an achievement of photoactive films based on all-polymer heterojunction films with in-plane optical anisotropy using a simple bottom-up self-assembly method. Both the donor (TQ1) and acceptor (N2200) polymers have the same spatial orientation with distinct anisotropy, approaching a dichroic ratio (DR) of 8. Polarization-sensitive light absorption is due to the uniaxially oriented polymer chains, which are dominated by lamellar packing with edge-on orientation. For IPPDs based on this anisotropic all-polymer heterojunction film, a photocurrent anisotropy was found with a polarized photocurrent ratio of 2.6. The detectivity of these IPPDs was found to be 1.9 × 1011 Jones (@ ∼600 nm, 0 V bias). Our work shows that oriented polymer donor–acceptor films fabricated using bottom-up self-assembly have great potential in applications, such as polarization detection.

Synthesis and Characterization of Hybrid Materials Derived from Conjugated Copolymers and Reduced Graphene Oxide.

In this study the preparation of hybrid materials based on reduced graphene oxide (rGO) and conjugated copolymers is reported. By tuning the number and arrangement of thiophenes in the main chain (indacenothiophene or indacenothienothiophene) and the nature of the polymer acceptor (difluoro benzothiadiazole or diketopyrrolopyrrole) semiconducting copolymers were synthesized through Stille aromatic coupling and characterized to determine their molecular characteristics. The graphene oxide was synthesized using the Staudenmaier method and was further modified to reduced graphene oxide prior to structural characterization. Various mixtures with different rGO quantities and conjugated copolymers were prepared to determine the optoelectronic, thermal and morphological properties. An increase in the maximum absorbance ranging from 3 to 6 nm for all hybrid materials irrespective of the rGO concentration, when compared to the pristine conjugated copolymers, was estimated through the UV-Vis spectroscopy indicating a differentiation on the optical properties. Through voltammetric experiments the oxidation and reduction potentials were determined and the calculated HOMO and LUMO levels revealed a decrease on the electrochemical energy gap for low rGO concentrations. The study indicates the potential of the hybrid materials consisting of graphene oxide and high band gap conjugated copolymers for applications related to organic solar cells.

Phase behavior of π-conjugated polymer and non-fullerene acceptor (PTB7-Th:ITIC) solutions and blends

Phase diagrams of ternary π-bonded polymer (PTB7-Th) solutions were constructed as a function of molecular weight, temperature, and electron acceptor species (ITIC, PC61BM and PC71BM). For this purpose, the Flory–Huggins lattice theory was employed with a constant χ interaction parameter, describing a binodal, spinodal, tie line, and critical point. Then, the morphologies of the blends composed of highly disordered PTB7-Th and crystallizable ITIC were investigated by atomic force microscopy. Subsequently, the surface polarities of the PTB7-Th:ITIC thin films were examined by water contact-angle goniometer, exhibiting a transition at the composition of ~ 60 ± 10 wt.% ITIC. Furthermore, X-ray diffraction indicated the presence of ITIC’s crystallites at ≥ 70 wt.% ITIC. Hence, the PTB7-Th:ITIC system was observed to undergo a phase transition at ~ 60–70 wt.% ITIC.

Linear Regulating of Polymer Acceptor Aggregation with Short Alkyl Chain Units Enhances All-Polymer Solar Cells' Efficiency.

The power conversion efficiency (PCE) of all-polymer solar cells (all-PSCs) has ascended rapidly arising from the development of polymerized small-molecule acceptor materials. However, numerous insulating long alkyl chains, which ensure the solubility of the polymer, result in inferior aggregation and charge mobility. Herein, this study proposes a facile random copolymerization strategy of two small molecule acceptor units with different lengths of alkyl side chains and synthesizes a series of polymer acceptors PYT-EHx, where x is the percentage of the short alkyl chain units. The aggregation strength and charge mobility of the acceptors rise linearly with increasing the proportion of short alkyl chain units. Thus, the PYT-EH20 reaches balanced aggregation with the star polymer donor PBDB-T, resulting in optimal morphology, fastest carrier transport, and reduced recombination and energy loss. Consequently, the PYT-EH20-based device yields a 14.8% PCE, a 16% improvement over the control PYT-EH0-based device, accompanied by an increase in open-circuit voltage (Voc ), short-circuit current density (Jsc ), and fill factor (FF). This work demonstrates that the random copolymerization strategy with short alkyl chain insertion is an effective avenue for developing high-performance polymer acceptors, which facilitates further advances in the efficiency of all-PSCs.

Intra- and intermolecular charge transfer control of symmetric A1–D–A2–D–A1 ladder-like small molecules/g-C3N4 heterojunctions for efficient photocatalytic sterilization and degradation from visible to near-infrared

Conjugated donor (D)–acceptor (A) polymer heterojunctions have developed as attractive photocatalysts. However, it is a great difficulty in precisely keeping the batch-to-batch reproducibility of polymers and controlling the related photocatalytic activity. Herein, three ladder-like small molecules BTx (BT2F, BTORCAE, and BTORIC2Cl) are synthesized via molecular engineering and the corresponding BTx/g-C3N4 heterojunctions are developed as photocatalysts for sterilization and contaminant degradation. It is demonstrated that employing another A unit into the D–A–D backbones of the small molecule could promote its intramolecular charge transfer and also improve the intermolecular charge transfer. Notably, BTORIC2Cl employing 2-(5,6-Dichloro-3-oxo-2,3 dihydro-1H-inden-1-ylidene)malononitrile as A1 unit in its symmetric A1–D–A2–D–A1 structure displays near-infrared absorption and extends the absorption edge of BTORIC2Cl/g-C3N4 to 850 nm. With the synergy of efficient intermolecular charge transfer, BTORIC2Cl/g-C3N4 contributes the champion photocatalytic activity of 98.9 % and 99.6 % antibacterial rates for Staphylococcus aureus and Escherichia coli. Moreover, the highest degradation reaction rate constant for Rhodamine B obtained by BTORIC2Cl/g-C3N4 is 5.7 times that of g-C3N4. This study proposes new ideas of fabricating small molecules/g-C3N4 OSHJs as photocatalysts via rational molecular engineering.

Benzotriazole-Featured Polymer Acceptors Toward As-Cast All-Polymer Solar Cells with a Remarkable Short-Circuit Current Density

Benzotriazole-Featured Polymer Acceptors Toward As-Cast All-Polymer Solar Cells with a Remarkable Short-Circuit Current Density

17.87% Efficiency All‐Polymer Tandem Solar Cell Enabled by Complementary Absorbing Polymer Acceptors

AbstractAll‐polymer solar cells (all‐PSCs) possess distinguished advantages of excellent morphology stability, thermal stability, and mechanical flexibility. Tandem solar cells, by stacking two sub‐cells, can absorb more photons in a wider wavelength range and can reduce thermal losses. However, limitation of polymer acceptors with suitable bandgaps hinders the development of tandem all‐PSCs. Herein, highly efficient tandem all‐PSCs are fabricated by employing two polymerized small molecular acceptors (PSMAs) of wide bandgap PIDT (1.66 eV) in the front cell and narrow bandgap PY‐IT (1.4 eV) in the rear cell. The two sub‐cells with the polymer donors of PM7 in front cell and PM6 in rear cell show high open circuit voltage (Voc) of 1.10 V for the front cell and 0.94 V for the rear cell. By rational device optimizations, the best power conversion efficiency of 17.87% is achieved for the tandem all‐PSCs with high Voc of 2.00 V. 17.87% is one of the highest efficiency for the all‐PSCs, and 2.00 V is one of the highest Voc for all the tandem organic solar cells. Moreover, the tandem all‐PSCs show excellent thermal and light‐soaking stability compared with their small‐molecule counterparts. The results provide insight to the potential of bandgap tuning in PSMAs, and indicate that the tandem architecture is an effective strategy to boost performance of the all‐PSCs.

Phenothiazine-Based Donor-Acceptor Polymers as Multifunctional Materials for Charge Storage and Solar Energy Conversion.

The increasing energy demand for diverse applications requires new types of devices and materials. Multifunctional materials that can fulfill different roles are of high interest as they can allow fabricating devices that can both convert and store energy. Herein, organic donor-acceptor redox polymers that can function as charge storage materials in batteries and as donor materials in bulk heterojunction (BHJ) photovoltaic devices are investigated. Based on its reversible redox chemistry, phenothiazine is used as the main building block in the conjugated copolymer design and combined with diketopyrrolopyrrol and benzothiadiazole as electron-poor comonomers to shift the optical absorption into the visible region. The resulting polymers show excellent cycling stability as positive electrode materials in lithium-organic batteries at discharge potentials of 3.6-3.7V versus Li/Li+ as well as good performances in BHJ solar cells with up to 1.9% power conversion efficiency. This study shows that the design of such multifunctional materials is possible, however, that it also faces challenges, as essential properties for good device function can lead to diametrically opposite requirements in materials design.

Benzotriazole‐Based Polymer Acceptor for High‐Efficiency All‐Polymer Solar Cells with High Photocurrent and Low Voltage Loss

AbstractThe power conversion efficiencies (PCEs) of all‐polymer solar cells (all‐PSCs) have already exceeded 17%. However, the limited absorption range of an all‐polymer system results in significantly reduced short‐circuit current density (Jsc), which eventually influences the PCE improvement. To broaden the light absorption of polymer acceptors, herein, benzotriazole is introduced in the core unit of small molecule acceptors and thus two narrow‐bandgap polymer acceptors named PTz‐BO and PTz‐C11 featuring the same molecular backbone and different side‐chain length are synthesized. Compared with PTz‐C11, the PTz‐BO based‐all PSCs deliver a slightly reduced Jsc, a large open‐circuit voltage (Voc) and a low voltage loss below 0.50 V. Moreover, ternary all‐PSCs are constructed by introducing PTz‐C11 as a guest component. Benefiting from the reduced recombination, improved exciton generation and dissociation, and balanced charge transport, a high efficiency of 16.58% is obtained for the ternary all‐PSCs, with a high Jsc over 25 mA cm−2 without sacrificing the Voc. Such result represents the highest efficiency reported for benzotriazole‐based all‐PSCs in the literature thus far. This work demonstrates the great potential of benzotriazole for the synthesis of efficient narrow‐bandgap polymer acceptors.

Constructing a Double-Cable Polymer Acceptor for Efficient All-Polymer Solar Cells with a Non-Radiative Recombination Energy Loss of 0.16 eV

Constructing a Double-Cable Polymer Acceptor for Efficient All-Polymer Solar Cells with a Non-Radiative Recombination Energy Loss of 0.16 eV

Revisiting the Bithiophene Imide‐Based Polymer Donors: Molecular Aggregation and Orientation Control Enabling New Polymer Donors for High‐Performance All‐Polymer Solar Cells†

Comprehensive SummaryBithiophene imide (BTI)‐based polymers have been promising photovoltaic materials due to their high mobility and tunable energy levels. However, BTI polymers have rarely been revisited since organic solar cells (OSCs) entered the era of non‐fullerene electron acceptors (NFEA) likely owing to their incompatibility with NFEAs. Herein, fine‐tuning the aggregation and orientation of BTI‐based donor‐π‐acceptor (D‐π‐A) polymer donors was achieved by incorporating the linear n‐octyl group into thiophene π‐bridge. The resulting polymer donor G15 shows excellent compatibility with NFEA L15 (polymer acceptor). The G15‐based all‐polymer OSCs achieve high power conversion efficiency of 15.17%. This is significantly higher than that (< 5%) of its analogue with isomerized branched alkyl chains and also among the highest values for all‐polymer OSCs. The results highlight that well‐tailored BTI polymer donors are attractive photovoltaic materials for further exploration in non‐fullerene organic solar cells.

Highly Flexible All‐Polymer Solar Cells Processed without Post‐Treatment Achieving 13.56% Efficiency

The many merits of organic solar cells such as light weight, flexibility, and printability rely heavily on flexible devices. In this regard, all‐polymer solar cells (PSCs) are the primary choices due to the superior flexibility and mechanical properties of polymers over small molecule and fullerene materials. However, the polymer batch discrepancy and the multifarious post‐treatment steps are serious obstacles to practical applications. Herein, highly efficient and mechanically robust all‐PSCs based on a new polymer acceptor PYSe‐2FT and polymer donor D18 are developed. Without any post‐treatment, the flexible all‐PSC exhibits high power conversion efficiency (PCE) of 13.56%, which stands among the best values in flexible all‐PSCs so far. Bending tests reveal that the flexible device maintains 86% efficiency of the original PCE after 1000 bending cycles with a narrow curvature radius of 3 mm. More importantly, the all‐PSC efficiencies are insensitive to the molecular weight of the newly developed acceptor polymer, which possesses favorable universality and stability when working together with various donors. The superior mechanical properties and the ease of process make this all‐PSC a promising candidate for applications in flexible and portable devices.

Recent progress in low‐cost noncovalently fused‐ring electron acceptors for organic solar cells

AbstractThe power conversion efficiencies (PCEs) of organic solar cells (OSCs) have improved considerably in recent years with the development of fused‐ring electron acceptors (FREAs). Currently, FREAs‐based OSCs have achieved high PCEs of over 19% in single‐junction OSCs. Whereas the relatively high synthetic complexity and the low yield of FREAs typically result in high production costs, hindering the commercial application of OSCs. In contrast, noncovalently fused‐ring electron acceptors (NFREAs) can compensate for the shortcomings of FREAs and facilitate large‐scale industrial production by virtue of the simple structure, facile synthesis, high yield, low cost, and reasonable efficiency. At present, OSCs based on NFREAs have exceeded the PCEs of 15% and are expected to reach comparable efficiency as FREAs‐based OSCs. Here, recent advances in NFREAs in this review provide insight into improving the performance of OSCs. In particular, this paper focuses on the effect of the chemical structures of NFREAs on the molecule conformation, aggregation, and packing mode. Various molecular design strategies, such as core, side‐chain, and terminal group engineering, are presented. In addition, some novel polymer acceptors based on NFREAs for all‐polymer OSCs are also introduced. In the end, the paper provides an outlook on developing efficient, stable, and low‐cost NFREAs for achieving commercial applications.

Y-Series-Based Polymer Acceptors for High-Performance All-Polymer Solar Cells in Binary and Non-binary Systems

Y-Series-Based Polymer Acceptors for High-Performance All-Polymer Solar Cells in Binary and Non-binary Systems

All-polymer solar cells: materials and devices

<p indent="0mm">Recently, organic solar cells (OSCs) have achieved rapid advance and the power conversion efficiency (PCE) of non-fullerene small molecular acceptors-based OSCs has exceeded 20%. All-polymer solar cells with blending active layer of polymer donors and polymer acceptors have attracted tremendous interest due to their outstanding advantages such as superior morphological and mechanical stability, which show great potential in large-area and flexible devices. With the emergence of various novel polymer donors/acceptors as well as the development of device architectures, the PCE of all-polymer solar cells has exceeded 18%. Nevertheless, compared with the non-fullerene small molecular acceptors-based OSCs, all-polymer solar cells encounter several problems, including relatively inferior device efficiency, batch-to-batch variation of the performance of polymer acceptors/donors. Therefore, it is still challenging to explore high-performance polymer donors/acceptors and prepare highly efficient devices. This review will pay attention to the development of polymer donors/acceptors, device manufacturing and interfacial layer engineering through systematically summarizing the recent representative literatures in this field, which will eventually provide prospects on the future development of materials and devices of all-polymer solar cells.

Impact of isomers on the photovoltaic properties of polymerized small-molecule acceptors

All-polymer solar cells (all-PSCs) have attracted tremendous research interests due to their inherent advantages of excellent mechanical flexibility, film formation, and morphological stability. Recently, the development of polymerized small-molecule acceptors (PSMAs) has boosted the power conversion efficiencies (PCEs) of all-PSCs to over 18%. Polymerization sites on the terminal groups of small molecule acceptors play a decisive role in determining the absorption spectra, frontier molecular orbital energy levels, molecular packing and crystallinity, charge carrier mobilities and device performance of polymer acceptors. In this perspective, we focus on the latest advances of region-specific terminal groups and region-regular PSMAs, aiming to summarize the relationship between molecular structure–physicochemical properties–active layer morphology–device performance. Finally, the future design directions and challenges faced by region-specific terminal groups and region-regular PSMAs are discussed. In this Perspective article, we advocate that the region-regular PSMAs approach can advance better designs for high-performance polymer acceptors with good batch-to-batch reproducibility.

An improved performance of all polymer solar cells enabled by sequential processing via non-halogenated solvents

Polymer acceptors based on the polymerization of small-molecule acceptor (PSMAs) have developed rapidly in recent years. All-polymer solar cells (all-PSCs) composed of PSMAs and polymer donors not only retain the excellent mechanical properties, but also have better morphological properties than traditional polymer acceptors such as N2200. However, since PSMAs are generally not highly polymerized, their electron mobilities are generally lower than the hole mobilities of the high-molecular-weight polymer donors they are used with. In this work, we apply the sequential processing (SqP) method and use toluene as the processing solvent to prepare PSMA-based all-PSCs, which effectively improves the electron mobility and shows much higher efficiency (15.8 %) than the SqP device prepared from chloroform (13.9 %) – the conventional solvent used for high-performance PSMAs. Not only that, the efficiency of the toluene-processed SqP device is also higher than that of the device prepared by the traditional blending-casting (BC) method (14.2 %). In addition, for the first time, we reveal the film formation process of all-polymer active layers prepared by the SqP method using the in situ UV-Vis absorption technique, and investigate the vertical phase separation and the rate of exciton generation across the device using film-depth-dependent absorption spectroscopy, which systematically explained the effect of increased mobility on device parameters. This methodology is applied in two different all-polymer systems, namely, PM6:PYF-T-o and PM6:PY-IT, and both systems manifest the same conclusion.