Tandem organic solar cells with 20.6% efficiency enabled by reduced voltage losses

High-Performance Intrinsically Stretchable Organic Photovoltaics Enabled by Robust Silver Nanowires/S-PH1000 Hybrid Transparent Electrodes

Intrinsically stretchable organic photovoltaics (is-OPVs) hold significant promise for integration into self-powered wearable electronics. However, their potential is hindered by the lack of sufficient consistency between optoelectronic and mechanical properties. This is primarily due to the limited availability of stretchable transparent electrodes (STEs) that possess both high conductivity and stretchability. Here, a hybrid STE with exceptional conductivity, stretchability, and thermal stability is presented. Specifically, STEs are composed of the modified PH1000 (referred to as S-PH1000) and silver nanowires (AgNWs). The S-PH1000 endows the STE with good stretchability and smoothens the surface, while the AgNWs enhance the charge transport. The resulting hybrid STEs enable is-OPVs to a remarkable power conversion efficiency (PCE) of 16.32%, positioning them among the top-performing is-OPVs. With 10% elastomer, the devices retain 82% of the initial PCE after 500 cycles at 20% strain. Additionally, OPVs equipped with these STEs exhibit superior thermal stability compared to those using indium tin oxide electrodes, maintaining 75% of the initial PCE after annealing at 85 °C for 390 h. The findings underscore the suitability of the designed hybrid electrodes for efficient and stable is-OPVs, offering a promising avenue for the future application of OPVs.

Designing A-D-A Type Fused-Ring Electron Acceptors with a Bulky 3D Substituent at the Central Donor Core to Minimize Non-Radiative Losses and Enhance Organic Solar Cell Efficiency

Designing and synthesizing narrow band gap acceptors that exhibit high photoluminescence quantum yield (PLQY) and strong crystallinity is a highly effective, yet challenging, approach to reducing non-radiative energy losses (▵Enr) and boosting the performance of organic solar cells (OSCs). We have successfully designed and synthesized an A-D-A type fused-ring electron acceptor, named DM-F, which features a planar molecular backbone adorned with bulky three-dimensional camphane side groups at its central core. These bulky substituents effectively hinder the formation of H-aggregates of the acceptors, promoting the formation of more J-aggregates and notably elevating the PLQY of the acceptor in the film. As anticipated, DM-F showcases pronounced near-infrared absorption coupled with impressive crystallinity. Organic solar cells (OSCs) leveraging DM-F exhibit a high EQEEL value and remarkably low ▵Enr of 0.14 eV-currently the most minimal reported value for OSCs. Moreover, the power conversion efficiency (PCE) of binary and ternary OSCs utilizing DM-F has reached 16.16 % and 20.09 %, respectively, marking a new apex in reported efficiency within the OSCs field. In conclusion, our study reveals that designing narrow band gap acceptors with high PLQY is an effective way to reduce ▵Enr and improve the PCE of OSCs.

What is the Limit Size of 2D Conjugated Extension on Central Units of Small Molecular Acceptors in Organic Solar Cells?

2D conjugated extension on central units of small molecular acceptors (SMAs) has gained great successes in reaching the state-of-the-art organic photovoltaics. Whereas the limit size of 2D central planes and their dominant role in constructing 3D intermolecular packing networks are still elusive. Thus, by exploring a series of SMAs with gradually enlarged central planes, it is demonstrated that, at both single molecular and aggerated levels, there is an unexpected blue-shift for their film absorption but preferable reorganization energies, exciton lifetimes and binding energies with central planes enlarging, especially when comparing to their Y6 counterpart. More importantly, the significance of well-balanced molecular packing modes involving both central and end units is first disclosed through a systematic single crystal analysis, indicating that when the ratio of central planes area/end terminals area is no more than 3 likely provides a preferred 3D intermolecular packing network of SMAs. By exploring the limit size of 2D central planes, This work indicates that the structural profiles of ideal SMAs may require suitable central unit size together with proper heteroatom replacement instead of directly overextending 2D central planes to the maximum. These results will likely provide some guidelines for future better molecular design.

Enhanced SWIR Light Detection in Organic Semiconductor Photodetectors through Up-Conversion of Mid-Gap Trap States

Shortwave-infrared (SWIR) photodetectors are vital for many scientific and industrial applications including surveillance, quality control and inspection. In recent decades, photodetectors based on organic semiconductors have emerged, demonstrating potential to add real value to broadband and narrowband imaging and sensing scenarios, where factors such as thermal budget sensitivity, large area aperture necessity, cost considerations, and lightweight and conformal flexibility demands are prioritized. It is now recognized that the performance of organic photodetectors (OPDs), notably their specific detectivity, is ultimately limited by trap states, universally present in disordered semiconductors. This work adopts an approach of utilizing these mid-gap states to specifically create a SWIR photo-response. To this end, this work introduces a somewhat counter-intuitive approach of "trap-doping" in bulk heterojunction (BHJs) photodiodes, where small quantities of a guest organic molecule are intentionally incorporated into a semiconducting donor:acceptor host system. Following this approach, this work demonstrates a proof-of-concept for a visible-to-SWIR broadband OPD, approaching (and, to some extent, even exceeding) state-of-the-art performance across critical photodetector metrics. The trap-doping approach is, even though only a proof-of-concept currently, broadly applicable to various spectral windows. It represents a new modality for engineering photodetection using the unconventional strategy of turning a limitation into a feature.

Small molecular donor materials based on β-β-bridged BODIPY dimers with a triphenylamine or carbazole unit for efficient organic solar cells

Herein, we have designed and synthesized two novel BODIPY dimer-based small molecules, denoted as ZMH-1 and ZMH-2, covalently linked and functionalized with triphenylamine (TPA) (ZMH-1) and carbazole (CZ) (ZMH-2) units as the electron donor at the 3- and 5-positions of the BODIPY core, respectively. Their optical and electrochemical properties were investigated. We have fabricated all small molecule bulk heterojunction organic solar cells using these BODIPY-based small molecules as electron donors along with fullerene derivative (PC71BM) and medium bandgap non-fullerene acceptor IDT-TC as electron acceptors. The optimized OSCs based on ZMH-1:PC71BM, ZMH-2:PC71BM, ZMH-1:IDT-IC, and ZMH-2:IDT-IC attain overall PCEs of 8.91%, 6.61%, 11.28%, and 5.48%, respectively. Moreover, when a small amount of PC71BM as guest acceptor is added to the binary host ZMH-1:IDT-TC and ZMH-2:IDT-TC, the ternary OSCs based on ZMH-1 and ZMH-2 reach PCEs of 13.70% and 12.71%, respectively.

Superior End-Group Stacking Promotes Simultaneous Multiple Charge-Transfer Mechanisms in Organic Solar Cells with an All-Fused-Ring Nonfullerene Acceptor

The all-fused-ring acceptor (AFRA) is a success for nonfullerene materials and has attracted considerable attention as its high optical and chemical stability expected to reduce energy loss, and power conversion efficiency (PCE) approaching 15% in constructed all-small-molecule organic solar cells (OSCs). Herein, the intrinsic role of the structure of AFRA F13 and the reason for its high PCE were revealed by comparison with those of typical fused acceptors IDT-IC and Y6. An increased degree of conjugation in F13 leads to broader and red-shifted absorption peaks, facilitating enhancement of the short-circuit current. Multiple charge-transfer mechanisms are mainly attributed to the higher Frenkel exciton (FE) state due to the multiple transition ways for acceptors in the C1-CN:F13 system. The increased number of atoms contributing to the charge-transfer (CT) state facilitated the existence of more superior stacking patterns with easy formation of CT and FE/CT states and a high charge separation rate. It was found using the AFRA is an effective strategy to enhance end-group stacking, enhancing the borrowing of oscillator strength to promote multiple CT mechanisms in the complexes, explaining the high performance of this OSC device. This work is promising to guide designing an efficient AFRA in the future.

Highly Efficient and Stable Organic Photovoltaic Cells for Underwater Applications

Organic photovoltaic (OPV) technology holds tremendous promise as a sustainable power source for underwater off-grid systems. However, research on underwater OPV cells is relatively scarce. Here, this gap is addressed by focusing on the exploration and development of OPV cells specifically designed for underwater applications. An acceptor, named ITO-4Cl, with excellent water resistance, is rationally designed and synthesized. Benefiting from its low energetic disorder and an absorption spectrum well-suited to the underwater environment, the ITO-4Cl-based OPV cell achieves an unprecedented power conversion efficiency (PCE) of over 25.6% at a water depth of 1 m. Additionally, under 660 nm laser irradiation, the cell demonstrates a notable PCE of 31.6%, indicating its potential for underwater wireless energy transfer. Due to the mitigation of thermal effects from solar irradiation, the lifetime of the ITO-4Cl-based OPV cell exceeds 7000 h. Additionally, a flexible OPV cell is fabricated that maintains its initial PCE even under exposure to high pressures of 5 MPa. A 32.5 cm2 flexible module achieves an excellent PCE of 17%. This work fosters a deeper understanding of underwater OPV cells and highlights the promising prospects of OPV cells for underwater applications.

Guest Acceptors with Lower Electrostatic Potential in Ternary Organic Solar Cells for Minimizing Voltage Losses

The ternary strategy, in which one guest component is introduced into one host binary system, is considered to be one of the most effective ways to realize high-efficiency organic solar cells (OSCs). To date, there is no efficient method to predict the effectiveness of guest components in ternary OSCs. Herein, three guest compositions (i.e., ANF-1, ANF-2 and ANF-3) with different electrostatic potential (ESP) are designed and synthesized by modulating the electron-withdrawing ability of the terminal groups through density functional theory simulations. The effects of the introduction of guest component into the host system (D18:N3) on the photovoltaic properties are investigated. The theoretical and experimental studies provide a key rule for guest acceptor in ternary OSCs to improve the open-circuit voltage, that is, the larger ESP difference between the guest and host acceptor, the stronger the intermolecular interactions and the higher the miscibility, which improves the luminescent efficiency of the blend film and the electroluminescence quantum yield (EQEEL) of the device by reducing the aggregation-caused-quenching, thereby effectively decreasing the non-radiative voltage loss of ternary OSCs. This work will greatly contribute to the development of highly efficient guest components, thereby promoting the rapid breakthrough of the 20% efficiency bottleneck for single-junction OSCs.

Three-in-One Strategy Enables Single-Component Organic Solar Cells with Record Efficiency and High Stability

Single-component organic solar cells (SCOSCs) with covalently bonding donor and acceptor are becoming increasingly attractive because of their superior stability over traditional multicomponent blend organic solar cells (OSCs). Nevertheless, the efficiency of SCOSCs is far behind the state-of-the-art multicomponent OSCs. Herein, by combination of the advantages of three-component and single-component devices, this work reports an innovative three-in-one strategy to boost the performance of SCOSCs. In this three-in-one strategy, three independent components (PM6, D18, and PYIT) are covalently linked together to create a new single-component active layer based on ternary conjugated block copolymer (TCBC) PM6-D18-b-PYIT by a facile polymerization. Precisely manipulating the component ratios in the polymer chains of PM6-D18-b-PYIT is able to broaden light utilization, promote charge dynamics, optimize, and stabilize film morphology, contributing to the simultaneously enhanced efficiency and stability of the SCOSCs. Ultimately, the PM6-D18-b-PYIT-based device exhibits a power conversion efficiency (PCE) of 14.89%, which is the highest efficiency of the reported SCOSCs. Thanks to the aggregation restriction of each component and chain entanglement in the three-in-one system, the PM6-D18-b-PYIT-based SCOSC displays significantly higher stability than the corresponding two-component (PM6-D18:PYIT) and three-component (PM6:D18:PYIT). These results demonstrate that the three-in-one strategy is facile and promising for developing SCOSCs with superior efficiency and stability.

Pyrrole-Based Fully Non-fused Acceptor for Efficient and Stable Organic Solar Cells

Organic solar cells (OSCs) are still suffering from the low light utilization and unstable under ultraviolet irradiation. To tackle these challenges, we design and synthesize a non-fused acceptor based on 1-(2-butyloctyl)-1H-pyrrole as π-bridge unit, denoted as GS70, which serves as active layer in the front-cell for constructing tandem OSCs with a parallel configuration. Benefiting from the well-complementary absorption spectra with the rear-cell, GS70-based parallel tandem OSCs exhibit an improved photoelectron response over the range between 600-700 nm, yielding a high short-circuit current density of 28.4 mA cm-2. The improvement in light utilization translates to a power conversion efficiency of 19.4 %, the highest value among all parallel tandem OSCs. Notably, owing to the intrinsic stability of GS70, the manufactured parallel tandem OSCs retain 84.9 % of their initial PCE after continuous illumination for 1000 hours. Overall, this work offers novel insight into the molecular design of low-cost and stability non-fused acceptors, emphasizing the importance of adopting a parallel tandem configuration for achieving efficient light harvesting and improved photostability in OSCs.

Molecular Design of Fully Nonfused Acceptors for Efficient Organic Photovoltaic Cells

The nonfused thiophene-benzene-thiophene (TBT) unit offers advantages in obtaining low-cost organic photovoltaic (OPV) materials due to its simple structure. However, OPV cells, including TBT-based acceptors, exhibit significantly lower energy conversion efficiencies. Here, we introduce a novel approach involving the design and synthesis of three TBT-based acceptors by substituting different position-branched side chains on the TBT unit. In comparison to TBT-10 and TBT-11, TBT-13, which exclusively incorporates α-position branched side chains with a large steric hindrance, demonstrates a more planar and stable conformation. When blended with the donor PBQx-TF, TBT-13-based blend film achieves favorable π-π stacking and aggregation characteristics, resulting in excellent charge transfer performance in the corresponding device. Due to the simultaneous enhancements in short-circuit current density and fill factor, the TBT-13-based OPV cell obtains an outstanding efficiency of 16.1%, marking the highest value for the cells based on fully nonfused acceptors. Our work provides a practical molecular design strategy for high-performance and low-cost OPV materials.

Tunable Donor Aggregation Dominance in a Ternary Matrix of All-Polymer Blends with Improved Efficiency and Stability

Using two structurally similar polymer acceptors in constructing high-efficiency ternary all-polymer solar cells is a widely acknowledged strategy; however, the focus thus far has not been on how polymer acceptor(s) would tune the aggregation of polymer donors, and furthermore film morphology and device performance (efficiency and stability). Herein, it is reported that matching of the celebrity acceptor PY-IT and the donor PBQx-TCl results in enhanced H-aggregation in PBQx-TCl, which can be finely tuned by controlling the amount of the second acceptor PY-IV. Consequently, the efficiency-optimized PY-IV weight ratio (0.2/1.2) leads to a state-of-the-art power conversion efficiency of 18.81%, wherein light-illuminated operational stability is also enhanced along with well-protected thermal stability. Such enhancements in the efficiency and operational and thermal stabilities of solar cells can be attributed to morphology optimization and the desired glass transition temperature of the target active layer based on comprehensive characterization. In addition to being a high-power conversion efficiency case for all-polymer solar cells, these enhancements are also a successful attempt for using combined acceptors to tune donor aggregation toward optimal morphology, which provides a theoretical basis for the construction of other types of organic photovoltaics beyond all-polymer solar cells.

Stability of organic solar cells: toward commercial applications

Organic solar cells (OSCs) have attracted a great deal of attention in the field of clean solar energy due to their advantages of transparency, flexibility, low cost and light weight. Introducing them to the market enables seamless integration into buildings and windows, while also supporting wearable, portable electronics and internet-of-things (IoT) devices. With the development of photovoltaic materials and the optimization of fabrication technology, the power conversion efficiencies (PCEs) of OSCs have rapidly improved and now exceed 20%. However, there is a significant lack of focus on material stability and device lifetime, causing a severe hindrance to commercial applications. In this review, we carefully review important strategies employed to improve the stability of OSCs over the past three years from the perspectives of material design and device engineering. Furthermore, we analyze and discuss the current important progress in terms of air, light, thermal and mechanical stability. Finally, we propose the future research directions to overcome the challenges in achieving highly stable OSCs. We expect that this review will contribute to solving the stability problem of OSCs, eventually paving the way for commercial applications in the near future.

Asymmetric Π-Bridge Engineering Enables High-Permittivity Benzo[1,2-B:4,5-b']Difuran-Conjugated Polymer for Efficient Organic Solar Cells

Organic solar cells (OSCs) exhibit complex charge dynamics, which are closely correlated with the dielectric constant (ɛr ) of photovoltaic materials. In this work, a series of novel conjugated copolymers based on benzo[1,2-b:4,5-b']difuran (BDF) and benzotriazole (BTz) is designed and synthesized, which differ by the nature of π-bridge from one another. The PBDF-TF-BTz with asymmetric furan and thiophene π-bridge demonstrates a larger ɛr of 4.22 than PBDF-dT-BTz with symmetric thiophene π-bridge (3.15) and PBDF-dF-BTz with symmetric furan π-bridge (3.90). The PBDF-TF-BTz also offers more favorable molecular packing and appropriate miscibility with non-fullerene acceptor Y6 than its counterparts. The corresponding PBDF-TF-BTz:Y6 OSCs display efficient exciton dissociation, fast charge transport and collection, and reduced charge recombination, eventually leading to a power conversion efficiency of 17.01%. When introducing a fullerene derivative (PCBO-12) as a third component, the PBDF-TF-BTz:Y6:PCBO-12 OSCs yield a remarkable FF of 80.11% with a high efficiency of 18.10%, the highest value among all reported BDF-polymer-based OSCs. This work provides an effective approach to developing high-permittivity photovoltaic materials, showcasing PBDF-TF-BTz as a promising polymer donor for constructing high-performance OSCs.

Regulating Phase Separation Kinetics for High-Efficiency and Mechanically Robust All-Polymer Solar Cells

All-polymer solar cells (all-PSCs) possess excellent operation stability and mechanical robustness than other types of organic solar cells, thereby attracting considerable attention for wearable flexible electron devices. However, the power conversion efficiencies (PCEs) of all-PSCs are still lagging behind those of small-molecule-acceptor-based systems owing to the limitation of photoactive materials and unsatisfactory blend morphology. In this work, a novel terpolymer, denoted as PBDB-TFCl (poly4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b″]dithiophene-1,3-bis(2-ethylhexyl)-5,7-di(thiophen-2-yl)-4H,8H-benzo[1,2-c:4,5-c″]dithiophene-4,8-dione-4,8-bis(4-chloro-5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene), is used as an electron donor coupled with a ternary strategy to optimize the performance of all-PSCs. The addition of PBDB-TCl unit deepens the highest occupied molecular orbital energy level, reducing voltage losses. Moreover, the introduction of the guest donor (D18-Cl) effectively regulates the phase-transition kinetics of PBDB-TFCl:D18-Cl:PY-IT during the film formation, leading to ideal size of aggregations and enhanced crystallinity. PBDB-TFCl:D18-Cl:PY-IT devices exhibit a PCE of 18.6% (certified as 18.3%), judged as the highest value so far obtained with all-PSCs. Besides, based on the ternary active layer, the manufactured 36 cm2 flexible modules exhibit a PCE of 15.1%. Meanwhile, the ternary PSCs exhibit superior photostability and mechanical stability. In summary, the proposed strategy, based on molecular design and the ternary strategy, allows optimization of the all-polymer blend morphology and improvement of the photovoltaic performance for stable large-scale flexible PSCs.

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.

Low-Cost Fully Non-fused Ring Acceptor Enables Efficient Organic Photovoltaic Modules for Multi-Scene Applications

Organic photovoltaic (OPV) cells, with highly tunable light-response ranges, offer significant potential for use in driving low-power consumption off-grid electronics in multi-scenarios. However, development of photoactive layer materials that can meet simultaneously the requirements of diverse irradiation conditions is a still challenging task. Herein, a low-cost fully non-fused acceptor (denoted as GS60) featuring well-matched absorption spectra with solar, scattered light and artificial light radiation was designed and synthesized. Systematic characterizations revealed that GS60 possessed outstanding photoelectron properties and ideal morphology, which resulted in reduced voltage loss and suppressed charge recombination. By blending with a non-fused ring polymer PTVT-T, the as-obtained GS60 based OPV cells achieved a good power conversion efficiency (PCE) of 14.1 %, a high value for the cells based on non-fused ring bulk heterojunction. Besides, manufactured large-area OPV modules based on PTVT-T:GS60 yielded PCEs of 11.2 %, 11.8 %, 12.1 %, 23.1 %, and 20.3 % under irradiation of AM 1.5G, natural light of cloudy weather, natural light in shadow, laser and indoor, respectively. The PTVT-T:GS60 devices exhibited considerable potential in terms of improving photostability and reducing material cost. Overall, this work provides novel insight into the molecular design of low-cost non-fused ring acceptors, and extended potential of medium band gap acceptors based OPV cells used in various application scenarios.

Step-by-Step Modulation of Crystalline Features and Exciton Kinetics for 19.2% Efficiency Ortho-Xylene Processed Organic Solar Cells

With plenty of popular and effective ternary organic solar cells (OSCs) construction strategies proposed and applied, its power conversion efficiencies (PCEs) have come to a new level of over 19% in single-junction devices. However, previous studies are heavily based in chloroform (CF) leaving behind substantial knowledge deficiencies in understanding the influence of solvent choice when introducing a third component. Herein, we present a case where a newly designed asymmetric small molecular acceptor using fluoro-methoxylated end-group modification strategy, named BTP-BO-3FO with enlarged bandgap, brings different morphological evolution and performance improvement effect on host system PM6:BTP-eC9, processed by CF and ortho-xylene (o-XY). With detailed analyses supported by a series of experiments, the best PCE of 19.24% for green solvent-processed OSCs is found to be a fruit of finely tuned crystalline ordering and general aggregation motif, which furthermore nourishes a favorable charge generation and recombination behavior. Likewise, over 19% PCE can be achieved by replacing spin-coating with blade coating for active layer deposition. This work focuses on understanding the commonly met yet frequently ignored issues when building ternary blends to demonstrate cutting-edge device performance, hence, will be instructive to other ternary OSC works in the future.

Donor-Acceptor Copolymers with 9-(2-Ethylhexyl)carbazole or Dibenzothiophene-5,5-dioxide Donor Units and 5,6-Difluorobenzo[c][1,2,5]thiadiazole Acceptor Units for Photonics

Semiconducting polymers, particularly of the third generation, including donor-acceptor (D-A) copolymers, are extensively studied due to their huge potential for photonic and electronic applications. Here, we report on two new D-A copolymers, CP1 and CP2, composed of different electron-donor (D) units: 9-(2-ethylhexyl)carbazole or dibenzothiophene-5,5-dioxide, respectively, and of 4,7-bis(4'-(2-octyldodecyl)thiophen-2'-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole building block with central 5,6-difluorobenzo[c][1,2,5]thiadiazole electron-acceptor (A) units, which were synthesized by Suzuki coupling in the high-boiling solvent xylene and characterized. The copolymers exhibited very good thermal and oxidation stability. A copolymer CP1 with different molecular weights was prepared in order to facilitate a comparison of CP1 with CP2 of comparable molecular weight and to reveal the relationship between molecular weight and properties. The photophysical, electrochemical, and electroluminescence properties were examined. Intense red photoluminescence (PL) with higher PL efficiencies for CP1 than for CP2 was observed in both solutions and films. Red shifts in the PL thin film spectra compared with the PL solution spectra indicated aggregate formation in the solid state. X-ray diffraction measurements revealed differences in the arrangement of molecules in thin films depending on the molecular weight of the copolymers. Light-emitting devices with efficient red emission and low onset voltages were prepared and characterized.

Ductile Oligomeric Acceptor-Modified Flexible Organic Solar Cells Show Excellent Mechanical Robustness and Near 18% Efficiency

High power conversion efficiency (PCE) and mechanical robustness are key requirements for wearable applications of organic solar cells (OSCs). However, almost all highly efficient photoactive films comprising polymer donors (PD ) and small molecule acceptors (SMAs) are mechanically brittle. In this study, highly efficient (PCE = 17.91%) and mechanically robust (crack-onset strain [COS] = 11.7%) flexible OSCs are fabricated by incorporating a ductile oligomeric acceptor (DOA) into the PD :SMA system, representing the most flexible OSCs to date. The photophysical, mechanical, and photovoltaic properties of D18:N3 with different DOAs are characterized. By introducing DOA DOY-C4 with a longer flexible alkyl linker and lower polymerization, the D18:N3:DOY-C4-based flexible OSCs exhibit a significantly higher PCE (17.91%) and 50% higher COS (11.7%) than the D18:N3-based device (PCE = 17.06%, COS = 7.8%). The flexible OSCs based on D18:N3:DOY-C4 retain 98% of the initial PCE after 2000 consecutive bending cycles, showing greater mechanical stability than the reference device (maintaining 89% of initial PCE). After careful investigation, it is hypothesized that the enhancement in mechanical properties is mainly due to the formation of tie chains or entanglement in the ternary blend films. These results demonstrate that DOAs have great potential for achieving high-performance flexible OSCs.

A-A Strategy Enables Desirable Performance of All-Polymer Solar Cells Fabricated with Nonhalogenated Solvents

Most polymer acceptors have been designed by applying a D (electron-rich unit)-A (electron-deficient unit) strategy, which are principally processed with halogenated solvents to fabricate all-polymer solar cells (all-PSCs). Two novel polymer acceptors, containing an A-A type backbone, were designed and synthesized, which can be readily dissolved in o-xylene. The polymer PY-FBTA, comprising a Y6 derivative as the first A unit and a benzotriazole derivative as the second A unit, shows smaller dihedral angles in the backbone, stronger molecular interactions, higher LUMO level, more complementary absorption spectrum, and better morphology with PM6 than the polymer PY-DPP comprising a diketopyrrolopyrrole derivative as the second A unit. Accordingly, the PM6:PY-FBTA all-PSC achieves a higher PCE of 13.95% than the all-PSC based on PM6:PY-DPP (9.51%) for thoroughly improved Jsc (22.34 mA cm-2), Voc (0.963 V), and FF (64.84%) values, which are fabricated with o-xylene as the solvent. This work demonstrates that the A-A structure is a desirable strategy for designing polymer acceptors for efficient all-PSCs prepared with nonhalogenated solvents.

Electronic Configuration Tuning of Centrally Extended Non-Fullerene Acceptors Enabling Organic Solar Cells with Efficiency Approaching 19

In the molecular optimizations of non-fullerene acceptors (NFAs), extending the central core can tune the energy levels, reduce nonradiative energy loss, enhance the intramolecular (donor-acceptor and acceptor-acceptor) packing, facilitate the charge transport, and improve device performance. In this study, a new strategy was employed to synthesize acceptors featuring conjugation-extended electron-deficient cores. Among these, the acceptor CH-BBQ, embedded with benzobisthiadiazole, exhibited an optimal fibrillar network morphology, enhanced crystallinity, and improved charge generation/transport in blend films, leading to a power conversion efficiency of 18.94 % for CH-BBQ-based ternary organic solar cells (OSCs; 18.19 % for binary OSCs) owing to its delicate structure design and electronic configuration tuning. Both experimental and theoretical approaches were used to systematically investigate the influence of the central electron-deficient core on the properties of the acceptor and device performance. The electron-deficient core modulation paves a new pathway in the molecular engineering of NFAs, propelling relevant research forward.

Regulating the Sequence Structure of Conjugated Block Copolymers Enables Large-Area Single-Component Organic Solar Cells with High Efficiency and Stability

Single-component organic solar cells (SCOSCs) based on conjugated block copolymers (CBCs) by covalently bonding a polymer donor and polymer acceptor become more and more appealing due to the formation of a favorable and stable morphology. Unfortunately, a deep understanding of the effect of the assembly behavior caused by the sequence structure of CBCs on the device performance is still missing. Herein, from the aspect of manipulating the sequence length and distribution regularity of CBCs, we synthesized a series of new CBCs, namely D18(20)-b-PYIT, D18(40)-b-PYIT and D18(60)-b-PYIT by two-pot polymerization, and D18(40)-b-PYIT(r) by traditional one-pot method. It is observed that precise manipulation of sequence length and distribution regularity of the polymer blocks fine-tunes the self-assembly of the CBCs, optimizes film morphology, improves optoelectronic properties, and reduces energy loss, leading to simultaneously improved efficiency and stability. Among these CBCs, the D18(40)-b-PYIT-based device achieves a high efficiency of 13.4 % with enhanced stability, which is an outstanding performance among SCOSCs. Importantly, the regular sequence distribution and suitable sequence length of the CBCs enable a facile film-forming process of the printed device. For the first time, the blade-coated large-area rigid/flexible SCOSCs are fabricated, delivering an impressive efficiency of 11.62 %/10.73 %, much higher than their corresponding binary devices.

Organic laser power converter for efficient wireless micro power transfer

Wireless power transfer with collimated power transmission and efficient conversion provides an alternative charging mode for off-grid and portable micro-power electronics. However, charging micro-power electronics with low photon flux can be challenging for current laser power converters. Here we show laser power converters with organic photovoltaic cells with good performance for application in laser wireless power transfer. The laser selection strategy is established and the upper limit of efficiency is proposed. The organic laser power converters exhibit a 36.2% efficiency at a 660 nm laser with a photon flux of 9.5 mW cm-2 and achieve wireless micro power transfer with an output of 0.5 W on a 2 meter scale. This work shows the good performance of organic photovoltaic cells in constructing organic laser power converters and provides a potential solution for the wireless power transfer of micro-power electronics.

Rational control of meniscus-guided coating for organic photovoltaics

Meniscus-guided coating exhibiting outstanding depositing accuracy, functional diversity, and operating convenience is widely used in printing process of photovoltaic electronics. However, current studies about hydrodynamic behaviors of bulk heterojunction ink are still superficial, and the key dynamic parameter dominating film formation is still not found. Here, we establish the principle of accurately evaluate the Hamaker constant and reveal the critical effect of precursor film length in determining flow evolution, the polymer aggregation, and final morphology. A shorter precursor film is beneficial to restraining chain relaxation, enhancing molecular orientation and mobility. On the basis of our precursor film-length prediction method proposed in this work, the optimal coating speed can be accurately traced. Last, a 18.39% power conversion efficiency has been achieved in 3-cm2 cell based on bulk heterojunction fabricated by blade coating, which shows few reduce from 19.40% in a 0.04-cm2 cell based on spin coating.