Regulation of Polymer Configurations Enables Green Solvent-Processed Large-Area Binary All-Polymer Solar Cells With Breakthrough Performance and High Efficiency Stretchability Factor

Dimerized Acceptors with Conjugate-Break Linker Enable Highly Efficient and Mechanically Robust Organic Solar Cells

Designing new acceptors is critical for intrinsically stretchable organic solar cells (IS-OSCs) with high efficiency and mechanical robustness. However, nearly all stretchable polymer acceptors exhibit limited efficiency and high-performance small molecular acceptors are very brittle. In this regard, we select thienylene-alkane-thienylene (TAT) as the conjugate-break linker and synthesize four dimerized acceptors by the regulation of connecting sites and halogen substitutions. It is found that the connecting sites and halogen substitutions considerably impact the overall electronic structures, aggregation behaviors, and charge transport properties. Benefiting from the optimization of the molecular structure, the dimerized acceptor exhibits rational phase separation within the blend films, which significantly facilitates exciton dissociation while effectively suppressing charge recombination processes. Consequently, FDY-m-TAT-based rigid OSCs render the highest power conversion efficiency (PCE) of 18.07 % among reported acceptors containing conjugate-break linker. Most importantly, FDY-m-TAT-based IS-OSCs achieve high PCE (14.29 %) and remarkable stretchability (crack-onset strain [COS]=18.23 %), significantly surpassing Y6-based counterpart (PCE=12.80 % and COS=8.50 %). To sum up, these findings demonstrate that dimerized acceptors containing conjugate-break linkers have immense potential in developing highly efficient and mechanically robust OSCs.

Binary All-polymer Solar Cells with a Perhalogenated-Thiophene-Based Solid Additive Surpass 18 % Efficiency

Morphological control of all-polymer blends is quintessential yet challenging in fabricating high-performance organic solar cells. Recently, solid additives (SAs) have been approved to be capable in tuning the morphology of polymer: small-molecule blends improving the performance and stability of devices. Herein, three perhalogenated thiophenes, which are 3,4-dibromo-2,5-diiodothiophene (SA-T1), 2,5-dibromo-3,4-diiodothiophene (SA-T2), and 2,3-dibromo-4,5-diiodothiophene (SA-T3), were adopted as SAs to optimize the performance of all-polymer organic solar cells (APSCs). For the blend of PM6 and PY-IT, benefitting from the intermolecular interactions between perhalogenated thiophenes and polymers, the molecular packing properties could be finely regulated after introducing these SAs. In situ UV/Vis measurement revealed that these SAs could assist morphological character evolution in the all-polymer blend, leading to their optimal morphologies. Compared to the as-cast device of PM6 : PY-IT, all SA-treated binary devices displayed enhanced power conversion efficiencies of 17.4-18.3 % with obviously elevated short-circuit current densities and fill factors. To our knowledge, the PCE of 18.3 % for SA-T1-treated binary ranks the highest among all binary APSCs to date. Meanwhile, the universality of SA-T1 in other all-polymer blends is demonstrated with unanimously improved device performance. This work provide a new pathway in realizing high-performance APSCs.

Acceptor-only oligomers with high coplanarity enable efficient and stable organic solar cells

Acceptor-only oligomers are developed as guest components to construct oligomer-assisted active layers for high performance organic solar cells. Due to the high planarity and structural similarity with the host polymer donor, BDD-based acceptor-only oligomers formed an alloy phase with PM6 and optimized the phase morphology effectively, achieving a stable device displaying 18% efficiency.

Achieving Record-High Stretchability and Mechanical Stability in Organic Photovoltaic Blends with a Dilute-absorber Strategy

Organic solar cells (OSCs) have potential for applications in wearable electronics. Except for high power conversion efficiency (PCE), excellent tensile properties and mechanical stability are required for achieving high-performance wearable OSCs, while the present metrics barely meet the stretchable requirements. Herein, this work proposes a facile and low-cost strategy for constructing intrinsically stretchable OSCs by introducing a readily accessible polymer elastomer as a diluent for all-polymer photovoltaic blends. Remarkably, record-high stretchability with a fracture strain of up to 1000% and mechanical stability with elastic recovery >90% under cyclic tensile tests are realized in the OSCs active layers for the first time. Specifically, the tensile properties of best-performing all-polymer photovoltaic blends are increased by up to 250 times after blending. Previously unattainable performance metrics (fracture strain >50% and PCE >10%) are achieved simultaneously for the resulting photovoltaic films. Furthermore, an overall evaluation parameter y is proposed for the efficiency-cost- stretchability balance of photovoltaic blend films. The y value of dilute-absorber system is two orders of magnitude greater than those of prior state-of-the-art systems. Additionally, intrinsically stretchable devices are prepared to showcase the mechanical stability. Overall, this work offers a new avenue for constructing and comprehensively evaluating intrinsically stretchable organic electronic films.

Polymer-Entangled Spontaneous Pseudo-Planar Heterojunction for Constructing Efficient Flexible Organic Solar Cells

Flexible organic solar cells (FOSCs) have attracted considerable attention from researchers as promising portable power sources for wearable electronic devices. However, insufficient power conversion efficiency (PCE), intrinsic stretchability, and mechanical stability of FOSCs remain severe obstacles to their application. Herein, an entangled strategy is proposed for the synergistic optimization of PCE and mechanical properties of FOSCs through green sequential printing combined with polymer-induced spontaneous gradient heterojunction phase separation morphology. Impressively, the toughened-pseudo-planar heterojunction (Toughened-PPHJ) film exhibits excellent tensile properties with a crack onset strain (COS) of 11.0%, twice that of the reference bulk heterojunction (BHJ) film (5.5%), which is among the highest values reported for the state-of-the-art polymer/small molecule-based systems. Finite element simulation of stress distribution during film bending confirms that Toughened-PPHJ film can release residual stress well. Therefore, this optimal device shows a high PCE (18.16%) with enhanced (short-circuit current density) JSC and suppressed energy loss, which is a significant improvement over the conventional BHJ device (16.99%). Finally, the 1 cm2 flexible Toughened-PPHJ device retains more than 92% of its initial PCE (13.3%) after 1000 bending cycles. This work provides a feasible guiding idea for future flexible portable power supplies.

Rapid Meniscus-Assisted Solution Printing of Large-Area Stripe Arrays of Highly Oriented Conjugated Polymers for Field-Effect Transistors

The ability to pattern semiconducting conjugated polymers (CPs) and concurrently enable their highly oriented chains represents an important endeavor to render their high charge mobility for electronic devices. However, simple yet generalizable routes to CPs with such desirable characteristics are limited. Herein, we report a robust meniscus-assisted solution printing (MASP) strategy to craft arrays of donor-acceptor CP stripes and scrutinize the correlation between different stripes and their charge transport attributes. Specifically, the MASP constrains the CP solution to evaporate between two nearly parallel plates with a stationary upper plate and a mobile lower plate containing periodic photoresist (PR) microchannels. Orchestrating the MASP speed comparable to the CP crystal growth rate yields CP stripe arrays with highly aligned CP crystals, resulting in the highest carrier mobility. Notably, our MASP technique can conveniently pattern other CPs of interest. It stands out as a simple strategy to impart large-scale production of functional materials for a wide range of applications in optics, electronics, sensors, etc.

Simple and Efficient Synthesis of Novel Tetramers with Enhanced Glass Transition Temperature for High-Performance and Stable Organic Solar Cells

Oligomer acceptors in organic solar cells (OSCs) have garnered substantial attention owing to their impressive power conversion efficiency (PCE) and long-term stability. However, the simple and efficient synthesis of oligomer acceptors with higher glass transition temperatures (Tg ) remains a formidable challenge. In this study, we propose an innovative strategy for the synthesis of tetramers, denoted as Tet-n, with elevated Tg s, achieved through only two consecutive Stille coupling reactions. Importantly, our strategy significantly reduces the redundancy in reaction steps compared to conventional methods for linear tetramer synthesis, thereby improving both reaction efficiency and yield. Furthermore, the OSC based on PM6:Tet-1 attains a high PCE of 17.32 %, and the PM6:L8-BO:Tet-1 ternary device achieves an even more higher PCE of 19.31 %. Remarkably, the binary device based on the Tet-1 tetramer demonstrates outstanding operational stability, retaining 80 % of the initial efficiency (T80 ) even after 1706 h of continuous illumination, which is primarily attributed to the enhanced Tg (247 °C) and lower diffusion coefficient (1.56×10-27  cm2  s-1 ). This work demonstrates the effectiveness of our proposed approach in the straightforward and efficient synthesis of tetramers materials with higher Tg s, thus offering a viable pathway for developing high-efficiency and stable OSCs.

Thorough Optimization for Intrinsically Stretchable Organic Photovoltaics

The development of intrinsically stretchable organic photovoltaics (is-OPVs) with a high efficiency is of significance for practical application. However, their efficiencies lag far behind those of rigid or even flexible counterparts. To address this issue, an advanced top-illuminated OPV is designed and fabricated, which is intrinsically stretchable and has a high performance, through systematic optimizations from material to device. First, the stretchability of the active layer is largely increased by adding a low-elastic-modulus elastomer of styrene-ethylene-propylene-styrene tri-block copolymer (SEPS). Second, the stretchability and conductivity of the opaque electrode are enhanced by a conductive polymer/metal (denoted as M-PH1000@Ag) composite electrode strategy. Third, the optical and electrical properties of a sliver nanowire transparent electrode are improved by a solvent vapor annealing strategy. High-performance is-OPVs are successfully fabricated with a top-illuminated structure, which provides a record-high efficiency of 16.23%. Additionally, by incorporating 5-10% elastomer, a balance between the efficiency and stretchability of the is-OPVs is achieved. This study provides valuable insights into material and device optimizations for high-efficiency is-OPVs, with a low-cost production and excellent stretchability, which indicates a high potential for future applications of OPVs.

Processability Considerations for Next-Generation Organic Photovoltaic Materials

The evolution of organic semiconductors for organic photovoltaics (OPVs) has resulted in unforeseen outcomes. This has provided substitute choices of photoactive layer materials, which effectively convert sunlight into electricity. Recently developed OPV materials have narrowed down the gaps in efficiency, stability, and cost in devices. Records now show power conversion efficiency in single-junction devices closing to 20%. Despite this, there is still a gap between the currently developed OPV materials and those that meet the requirements of practical applications, especially the solution processability issue widely concerned in the field of OPVs. Based on the general rule that structure determines properties, methodologies to enhance the processability of OPV materials are reviewed and explored from the perspective of material design and views on the further development of processable OPV materials are presented. Considering the current dilemma that the existing evaluation indicators cannot reflect the industrial processability of OPV materials, a more complete set of key performance indicators are proposed for their processability considerations. The purpose of this perspective is to raise awareness of the boundary conditions that exist in industrial OPV manufacturing and to provide guidance for academic research that aspires to contribute to technological advancements.

Central Core Substitutions and Film-Formation Process Optimization Enable Approaching 19% Efficiency All-Polymer Solar Cells

Molecular interactions and film-formation processes greatly impact the blend film morphology and device performances of all-polymer solar cells (all-PSCs). Molecular structure, such as the central cores of polymer acceptors, would significantly influence this process. Herein, the central core substitutions of polymer acceptors are adjusted and three quinoxaline (Qx)-fused-core-based materials, PQx1, PQx2, and PQx3 are synthesized. The molecular aggregation ability and intermolecular interaction are systematically regulated, which subsequently influence the film-formation process and determine the resulting blend film morphology. As a result, PQx3, with favorable aggregation ability and moderate interaction with polymer donor PM6, achieves efficient all-PSCs with a high power conversion efficiency (PCE) of 17.60%, which could be further improved to 18.06% after carefully optimizing device annealing and interface layer. This impressive PCE is one of the highest values for binary all-PSCs based on the classical polymer donor PM6. PYF-T-o is also involved in promoting light utilization, and the resulting ternary device shows an impressive PCE of 18.82%. In addition, PM6:PQx3-based devices exhibit high film-thickness tolerance, superior stability, and considerable potential for large-scale devices (16.23% in 1 cm2 device). These results highlight the importance of structure optimization of polymer acceptors and film-formation process control for obtaining efficient and stable all-PSCs.

Suppressing electron-phonon coupling in organic photovoltaics for high-efficiency power conversion

The nonradiative energy loss (∆Enr) is a critical factor to limit the efficiency of organic solar cells. Generally, strong electron-phonon coupling induced by molecular motion generates fast nonradiative decay and causes high ∆Enr. How to restrict molecular motion and achieve a low ∆Enr is a sticking point. Herein, the free volume ratio (FVR) is proposed as an indicator to evaluate molecular motion, providing new molecular design rationale to suppress nonradiative decay. Theoretical and experimental results indicate proper proliferation of alkyl side-chain can decrease FVR and restrict molecular motion, leading to reduced electron-phonon coupling while maintaining ideal nanomorphology. The reduced FVR and favorable morphology are simultaneously obtained in AQx-6 with pinpoint alkyl chain proliferation, achieving a high PCE of 18.6% with optimized VOC, JSC and FF. Our study discovered aggregation-state regulation is of great importance to the reduction of electron-phonon coupling, which paves the way to high-efficiency OSCs.

All-Polymer Solar Cells Sequentially Solution Processed from Hydrocarbon Solvent with a Thick Active Layer

Organic solar cells (OSCs) have gained increasing attention. Among the various directions in OSCs, all-polymer solar cells (all-PSCs) have emerged as a highly promising and currently active research area due to their excellent film formation properties, mechanical properties, and thermal stabilities. However, most of the high-efficiency all-PSCs are processed from chloroform with an active layer thickness of ~100 nm. In order to meet the requirements for industrialization, a thicker active layer processed from low-vapor pressure solvents (preferentially a hydrocarbon solvent) is strongly desired. Herein, we employ toluene (a hydrocarbon solvent with a much higher boiling point than chloroform) and a method known as sequential processing (SqP) to mitigate the rapid decline in efficiency with increasing film thickness. We show that SqP enables a more favorable vertical phase segregation that leads to less trap-assisted recombination and enhanced charge extraction and lifetime than blend-cast devices at higher film thicknesses.