Nonfused-Core-Small-Molecule-Acceptor-Based Polymer Acceptors for All-Polymer Solar Cells

Chinese Journal of Polymer Science - Polymerizing the narrow bandgap small-molecule architecture with a conjugated linking unit (or called the polymerized small molecule acceptors (PSMAs)) is a...     

Polymer Acceptors for High-Performance All-Polymer Solar Cells

All-polymer solar cells (all-PSCs) have attracted considerable attention owing to their pronounced advantages of excellent mechanical flexibility/stretchability and greatly enhanced device stability as compared to other types of organic solar cells (OSCs). Thanks to the extensive research efforts dedicated to the development of polymer acceptors, all-PSCs have achieved remarkable improvement of photovoltaic performance, recently. This review summarizes the recent progress of polymer acceptors based on the key electron-deficient building blocks, which include bithiophene imide (BTI) derivatives, boron-nitrogen coordination bond (B←N)-incorporated (hetero)arenes, cyano-functionalized (hetero)arenes, and fused-ring electron acceptors (FREAs). In addition, single-component-based all-PSCs are also briefly discussed. The structure-property correlations of polymer acceptors are elaborated in detail. Finally, we offer our insights into the development of new electron-deficient building blocks with further optimized properties and the polymers built from them for efficient all-PSCs.     

含萘并二噻吩小分子受体材料的带隙调控及其在非富勒烯太阳能电池中的应用

By using photovoltaic technology, ambient solar light can be directly converted to electricity. The photovoltaic technology has been regarded as one of the most important and promising strategies to resolve the worldwide energy and pollution problems. As one type of photovoltaic technology, polymer solar cells have attracted increasing interest due to their advantages of solution processing capability, low-cost, feasibility to be fabricated on flexible substrates etc. Not until a few years ago, the fullerene derivatives had been dominated the organic photovoltaic field as the most promising acceptor materials for polymer solar cells. However, fullerene-based polymer solar cells have a power conversion efficiency bottleneck due to the relatively fixed energy levels as well as the fixed bandgaps of fullerene derivatives. Therefore, researchers started to develop nonfullerene acceptors which can be used as alternatives to replace the traditional fullerene derivatives. Compared to the fullerene derivatives, nonfullerene acceptors offer several advantages such as stronger light absorption, tunable bandgaps and frontier molecular orbital energy levels. For nonfullerene acceptors, a ladder-type fused ring is usually used as the central core which is an essential building block to tailor the bandgaps and energy levels. Although many fused ring systems have been explored for efficient nonfullerene acceptors, ladder-type angular-shape dithienonaphthalene is seldom reported as the donor unit for nonfullerene acceptors. Furthermore, the impact of thiophene bridge on the optical and photovoltaic properties of the dithienonaphthalene-based nonfullerene acceptors has never been reported. In this context, we report on the design and synthesis of a dithienonaphthalene-based small-molecule acceptor which contains thiophene bridges in between the acceptor terminals and the fused-ring donor core. Compared to the dithienonaphthalene-based small-molecule without the thiophene bridges, the resulting acceptor (DTNIT) exhibits a reduced bandgap of 1.52 eV which makes it more suitable to be blended with the benchmark large bandgap copolymer, poly[(2, 6-(4, 8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1, 2-b: 4, 5-b']dithiophene))-alt-(5, 5-(1', 3'-di-2-thienyl-5', 7'-bis(2-ethylhexyl)benzo[1', 2'-c:4', 5'-c']dithiophene-4, 8-dione)] (PBDB-T). The reduced band-gap of the resulting nonfullerene acceptor can be attributed to its extended π-conjugation in comparison with the dithienonaphthalene-based acceptor without the thiophene bridges. Inverted polymer solar cells with a device configuration of indium tin oxide/ZnO/PBDB-T:DTNIT/MoO₃/Ag were fabricated and characterized. Polymer solar cells based on PBDB-T:DTNIT showed an open circuit voltage of 0.91 V, an enhanced short circuit current of 14.42 mA∙cm⁻², and a moderate PCE of 7.05% which is comparable to the PCE of 7.12% for the inverted device based on PBDB-T:PC₇₁BM. Our results not only provide a method to synthesize efficient nonfullerene acceptors with reduced bandgaps, but also offer a bandgap modulation strategy for nonfullerene acceptors.     

Recent Research Progress of n-Type Conjugated Polymer Acceptors and All-Polymer Solar Cells

The active layer of all polymer solar cells(all-PSCs) is composed of a blend of a p-type conjugated polymer(p-CP) as donor and an n-type conjugated polymer(n-CP) as acceptor. All-PSCs possess the advantages of light weight, thin active layer, mechanical flexibility, low cost solution processing and high stability, but the power conversion efficiency(PCE) of the all-PSCs was limited by the poor photovoltaic performance of the n-CP acceptors before 2016. Since the report of the strategy of polymer...     

Unaxisymmetric Non-Fused Electron Acceptors for Efficient Polymer Solar Cells

Chinese Journal of Polymer Science - To develop photovoltaics embracing the both features of high performance and low cost has drawn attentions of researchers, yet representing the significant...     

A Non-Conjugated Polymer Acceptor for Efficient and Thermally Stable All-Polymer Solar Cells

A non-conjugated polymer acceptor PF1-TS4 was firstly synthesized by embedding a thioalkyl segment in the mainchain, which shows excellent photophysical properties on par with a fully conjugated polymer, with a low optical band gap of 1.58 eV and a high absorption coefficient >10⁵ cm⁻¹, a high LUMO level of −3.89 eV, and suitable crystallinity. Matched with the polymer donor PM6, the PF1-TS4-based all-PSC achieved a power conversion efficiency (PCE) of 8.63 %, which is ≈45 % higher than that of a device based on the small molecule acceptor counterpart IDIC16. Moreover, the PF1-TS4-based all-PSC has good thermal stability with ≈70 % of its initial PCE retained after being stored at 85 °C for 180 h, while the IDIC16-based device only retained ≈50 % of its initial PCE when stored at 85 °C for only 18 h. Our work provides a new strategy to develop efficient polymer acceptor materials by linkage of conjugated units with non-conjugated thioalkyl segments.     

Planarized Polymer Acceptor Featuring High Electron Mobility for Efficient All-Polymer Solar Cells

Chinese Journal of Polymer Science - Significant progress has been achieved for all-polymer solar cells (APSCs) in the last few years by the use of polymerized small molecular acceptors (PSMAs)....     

Unfused-ring Acceptors with Dithienobenzotriazole Core for Efficient Organic Solar Cells

In recent years, non-fullerene acceptors(NFAs) with unfused-ring structure have received extensive attention due to their flexible combination of building blocks and relatively simple synthetic routes. In this work, three new A-D-C-D-A type unfused-ring acceptors(UFAs),named DTBTz EH-IC2F, DTBTz Me-IC2F and DTBTz Me-IC2Cl, were designed and synthesized with dithienobenzotriazole(DTBTz) as the core.Through modification of alkyl chain on the DTBTz unit and change of halogen atoms on the cyanoindan...     

Oligomerized Fused-Ring Electron Acceptors for Efficient and Stable Organic Solar Cells

Organic solar cells (OSCs) have attracted wide research attention in the past decades. Very recently, oligomerized fused-ring electron acceptors (OFREAs) have emerged as a promising alternative to small-molecular/polymeric acceptor-based OSCs due to their unique advantages such as well-defined structures, batch reproducibility, good film formation, low diffusion coefficient, and excellent stability. So far, rapid advances have been made in the development of OFREAs consisting of directly/rigidly/flexibly linked oligomers and fused ones. In this Minireview, we systematically summarized the recent research progress of OFREAs, including structural diversity, synthesis approach, molecular conformation and packing, and long-term stability. Finally, we conclude with future perspectives on the challenges to be addressed and potential research directions. We believe that this Minireview will encourage the development of novel OFREAs for OSC applications.     

Advances in Green-Solvent-Processable All-Polymer Solar Cells

All-polymer solar cells(all-PSCs) have significantly improved long-term stability and mechanical stretchability. The power conversion efficiency(PCE) of all-PSCs has been rapidly improved from ～1% to now over ～17%, driven by rational molecular design, blend morphology optimization, and device engineering. However, most all-PSCs are generally processed with halogenated solvents, hazardous for human health and the global environment. Achieving high-performance all-PSCs with halogen-free solvent pr...     

Perylene Diimide-Based Conjugated Polymers for All-Polymer Solar Cells

In recent decades, non-fullerene acceptors (NFAs) are undergoing rapid development and emerging as a hot area in the field of organic solar cells. Among the high-performance non-fullerene acceptors, aromatic diimide-based electron acceptors remain to be highly promising systems. This review discusses the important progress of perylene diimide (PDI)-based polymers as non-fullerene acceptors in all-polymer solar cells (all-PSCs) since 2014. The relationship between structure and property, matching aspects between donors and acceptors, and device fabrications are unveiled from a synthetic chemist perspective.     

稠环电子受体光伏材料

基于非富勒烯受体的有机太阳能电池是化学和材料领域的热点前沿之一,中国领跑这个热点前沿.中国学者在非富勒烯受体材料方面取得了一系列重要的创新成果.我们提出了"稠环电子受体(FREA)"这一新概念,构建了高性能稠环电子受体新体系,发明了明星分子ITIC.我们的原创性工作引起了国内外同行的广泛关注和跟进.目前,基于稠环电子受体的有机太阳能电池效率已达到13%~14%,超过富勒烯体系.ITIC等稠环电子受体的出现颠覆了富勒烯受体在有机太阳能电池领域的统治地位,开创了有机太阳能电池的非富勒烯时代.本文简要评述了我们在高性能稠环电子受体设计与器件应用中的研究进展,并展望稠环电子受体的未来发展.     

Triplet Acceptors with a D-A Structure and Twisted Conformation for Efficient Organic Solar Cells

Triplet acceptors have been developed to construct high-performance organic solar cells (OSCs) as the long lifetime and diffusion range of triplet excitons may dissociate into free charges instead of net recombination when the energy levels of the lowest triplet state (T₁) are close to those of charge-transfer states (³CT). The current triplet acceptors were designed by introducing heavy atoms to enhance the intersystem crossing, limiting their applications. Herein, two twisted acceptors without heavy atoms, analogues of Y6, constructed with large π-conjugated core and D-A structure, were confirmed to be triplet materials, leading to high-performance OSCs. The mechanism of triplet excitons were investigated to show that the twisted and D-A structures result in large spin–orbit coupling (SOC) and small energy gap between the singlet and triplet states, and thus efficient intersystem crossing. Moreover, the energy level of T₁ is close to ³CT, facilitating the split of triplet exciton to free charges.     

Lowly Fused Non-Fullerene Acceptors Towards Efficient Organic Solar Cells Enabled by Isomerization

Chinese Journal of Polymer Science - Two lowly fused non-fullerene acceptors (NFAs) with isomeric structures, named as BTP-out-4F and BTP-in-4F, were developed by tailoring the fused 7-ring central...     

N-Type Quinoidal Polymers Based on Dipyrrolopyrazinedione for Application in All-Polymer Solar Cells

Conjugated molecules and polymers with intrinsic quinoidal structure are promising n-type organic semiconductors, which have been reported for application in field-effect transistors and thermoelectric devices. In principle, the molecular and electronic characteristics of quinoidal polymers can also enable their application in organic solar cells. Herein, two quinoidal polymers, named PzDP-T and PzDP-ffT, based on dipyrrolopyrazinedione were synthesized and used as electron acceptors in all-polymer solar cells (all-PSCs). Both PzDP-T and PzDP-ffT showed suitable energy levels and wide light absorption range that extended to the near-infrared region. When combined with the polymer donor PBDB-T, the resulting all-PSCs based on PzDP-T and PzDP-ffT exhibited a power conversion efficiency (PCE) of 1.33 and 2.37 %, respectively. This is the first report on the application of intrinsic quinoidal conjugated polymers in all-PSCs. The photovoltaic performance of the all-PSCs was revealed to be mainly limited by the relatively poor and imbalanced charge transport, considerable charge recombination. Detailed investigations on the structure-performance relationship suggested that synergistic optimization of light absorption, energy levels, and charge transport properties is needed to achieve more successful application of intrinsic quinoidal conjugated polymers in all-PSCs.     

Triplet Acceptors with a D‐A Structure and Twisted Conformation for Efficient Organic Solar Cells

Triplet acceptors have been developed to construct high‐performance organic solar cells (OSCs) as the long lifetime and diffusion range of triplet excitons may dissociate into free charges instead of net recombination when the energy levels of the lowest triplet state (T₁) are close to those of charge‐transfer states (³CT). The current triplet acceptors were designed by introducing heavy atoms to enhance the intersystem crossing, limiting their applications. Herein, two twisted acceptors without heavy atoms, analogues of Y6, constructed with large π‐conjugated core and D‐A structure, were confirmed to be triplet materials, leading to high‐performance OSCs. The mechanism of triplet excitons were investigated to show that the twisted and D‐A structures result in large spin–orbit coupling (SOC) and small energy gap between the singlet and triplet states, and thus efficient intersystem crossing. Moreover, the energy level of T₁ is close to ³CT, facilitating the split of triplet exciton to free charges.     

Triplet Tellurophene‐Based Acceptors for Organic Solar Cells

Triplet materials have been employed to achieve high‐performing organic solar cells (OSCs) by extending the exciton lifetime and diffusion distances, while the triplet non‐fullerene acceptor materials have never been reported for bulk heterojunction OSCs. Herein, for the first time, three triplet molecular acceptors based on tellurophene with different degrees of ring fusing were designed and synthesized for OSCs. Significantly, these molecules have long exciton lifetime and diffusion lengths, leading to efficient power conversion efficiency (7.52 %), which is the highest value for tellurophene‐based OSCs. The influence of the extent of ring fusing on molecular geometry and OSCs performance was investigated to show the power conversion efficiencies (PCEs) continuously increased along with increasing the extent of ring fusing.     

A Near-Infrared Polymer Acceptor Enables over 15% Efficiency for All-Polymer Solar Cells

Finding effective molecular design strategies to enable efficient charge generation, high charge transport, and small energy loss is a longstanding challenge for developing high-performance all-polymer solar cells(all-PSCs). Here, we designed and synthesized a fused-aromaticring-constructed near-infrared(NIR) polymer acceptor(PA) PYT-Tz with fused-ring benzotriazole(BTz)-based A’-DAD-A’ structure as electrondeficient-core, n-nonane as alkyl-side-chain and thiophene as π-bridge, and achieved a po...