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The determination of molecular conformations of oligomeric acceptors (OAs) and their impact on molecular packing are crucial for understanding the photovoltaic performance of their resulting polymer solar cells (PSCs) but have not been well studied yet. Herein, we synthesized two dimeric acceptor materials, DIBP3F‐Se and DIBP3F‐S, which bridged two segments of Y6‐derivatives by selenophene and thiophene, respectively. Theoretical simulation and experimental 1D and 2D NMR spectroscopic studies prove that both dimers exhibit O‐shaped conformations other than S‐ or U‐shaped counter‐ones. Notably, this O‐shaped conformation is likely governed by a distinctive "conformational lock" mechanism, arising from the intensified intramolecular π–π interactions among their two terminal groups within the dimers. PSCs based on DIBP3F‐Se deliver a maximum efficiency of 18.09 %, outperforming DIBP3F‐S‐based cells (16.11 %) and ranking among the highest efficiencies for OA‐based PSCs. This work demonstrates a facile method to obtain OA conformations and highlights the potential of dimeric acceptors for high‐performance PSCs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Regulating molecular structure to optimize the active layer morphology is of considerable significance for improving the power conversion efficiencies (PCEs) in organic solar cells (OSCs). Herein, we demonstrated a simple ternary copolymerization approach to develop a terpolymer donor PM6‐Tz20 by incorporating the 5,5′‐dithienyl‐2,2′‐bithiazole (DTBTz, 20 mol%) unit into the backbone of PM6 (PM6‐Tz00). This method can effectively tailor the molecular orientation and aggregation of the polymer, and then optimize the active layer morphology and the corresponding physical processes of devices, ultimately boosting FF and then PCE. Hence, the PM6‐Tz20: Y6‐based OSCs achieved a PCE of up to 17.1% with a significantly enhanced FF of 0.77. Using Ag (220 nm) instead of Al (100 nm) as cathode, the champion PCE was further improved to 17.6%. This work provides a simple and effective molecular design strategy to optimize the active layer morphology of OSCs for improving photovoltaic performance. [ABSTRACT FROM AUTHOR]

The prosperous period of polymer solar cells (PSCs) has witnessed great progress in molecule design methods to promote power conversion efficiency (PCE). Designing asymmetric structures has been proved effective in tuning energy level and morphology, which has drawn strong attention from the PSC community. Two hepta‐ring and octa‐ring asymmetric small molecular acceptors (SMAs) (IDTP‐4F and IDTTP‐4F) with S‐shape and C‐shape confirmations are developed to study the relationship between conformation shapes and PSC efficiencies. The similarity of absorption and energy levels between two SMAs makes the conformation a single variable. Additionally, three wide‐bandgap polymer donors (PM6, S1, and PM7) are chosen to prove the universality of the relationship between conformation and photovoltaic performance. Consequently, the champion PCE afforded by PM7: IDTP‐4F is as high as 15.2% while that of PM7: IDTTP‐4F is 13.8%. Moreover, the S‐shape IDTP‐4F performs obviously better than their IDTTP‐4F counterparts in PSCs regardless of the polymer donors, which confirms that S‐shape conformation performs better than the C‐shape one. This work provides an insight into how conformations of asymmetric SMAs affect PCEs, specific functions of utilizing different polymer donors to finely tune the active‐layer morphology and another possibility to reach an excellent PCE over 15%. [ABSTRACT FROM AUTHOR]

Keywords: Acceptor; Molecular Conformation; Oligomer; Selenophene; Solar Cells EN Acceptor Molecular Conformation Oligomer Selenophene Solar Cells 1 1 1 10/31/23 20231106 NES 231106 B Two dimeric acceptors b , DIBP3F-Se and DIBP3F-S were synthesized by linking two Y6-derivative segments using different central linking bridges: selenophene and thiophene. Paired with the state-of-the-art polymer donor PM6, optimized solar cells employing DIBP3F-Se showcase remarkable performance with a power conversion efficiency of 18.09 %, as demonstrated by Donghong Yu, Thomas D. Anthopoulos, Ergang Wang et al. in their Research Article (e202302888). Back Cover: On the Conformation of Dimeric Acceptors and Their Polymer Solar Cells with Efficiency over 18 % (Angew. [Extracted from the article]

In this work, polymer solar cells are fabricated based on the blend of PTB7-Th: PC71BM by using a mixed solvent additive of 1,8-diiodooctane and N-methyl pyrrolidone to optimize the morphology of the blend. A high power conversion efficiency (PCE) of 10.8% has been achieved with a simple conventional device. In order to deeply investigate the influence of the mixed solvent additives on the morphology and device performance, the variations of the molecular packing and bulk morphology of the blend film cast from ortho-dichlorobenzene with single or binary solvent additives are measured. Although all the blend films exhibit similar domain size and nanoscale phase separation, the blend film processed with mixed solvent additive shows the highest domain purity, resulting in the least bimolecular recombination, relatively high Jsc and FF, and hence enhanced PCE. Therefore, the best photovoltaic performance with the Voc of 0.82 V, Jsc of 19.1 mA cm−2, FF of 69.1%, and PCE of 10.8% are obtained for the device based on the blend with binary solvent additive treatment. [ABSTRACT FROM AUTHOR]

Herein, three small molecule (SM)‐acceptors (POIT‐IC, POIT‐IC2F, and POIT‐IC4F) are developed by combining the side‐chain engineering located on the sp3‐hybridized carbon atoms of the fused‐ring core and the fluorination of end groups. From ITIC to POIT‐IC, POIT‐IC2F, and then to POIT‐IC4F, the SM‐acceptors show gradually broadened absorption spectra, increased maximum extinction coefficient, crystallinity, and electron mobilities due to the synergistic effects of side‐chain engineering and fluorination. Compared with nonfluorinated ITIC and POIT‐IC, as fluorination broadens the molecular spectra, POIT‐IC2F and POIT‐IC4F with alkoxyphenyl side chains show less decreased LUMO levels than IT‐IC2F and IT‐IC4F with alkylphenyl side chains, which are conducive to both higher Voc and Jsc for organic solar cells (OSCs). Combined with polymer donor PM6, the POIT‐IC4F‐based OSCs achieve a device efficiency of up to 13.8% with a high Voc of 0.91 V and Jsc of 20.9 mA cm−2, which are significantly higher than that of the control OSCs based on ITIC (8.9%), POIT‐IC (10.1%), or IT‐IC4F (12.2%). An efficiency of 13.8% is one of the highest PCEs reported for the annealing‐free OSCs. Our results show that the synergistic effects of side‐chain engineering and fluorination on SM‐acceptor can simultaneously broaden spectral response and minimize voltage loss of OSCs and ultimately achieve high device efficiency. [ABSTRACT FROM AUTHOR]

Generally, highly efficient organic solar cells require both a high open‐circuit voltage (VOC) and a high short‐circuit current density (JSC). Reducing the energy loss (Eloss) is an effective way to achieve a high VOC without compromising the photocurrent, which is ideal for enhancing the power conversion efficiencies (PCEs). Herein, a new chlorinated nonfullerene acceptor (ITC‐2Cl) with chlorinated thiophene‐fused end groups is developed. In comparison with the unchlorinated counterpart (ITCPTC), the introduction of Cl improves not only the electronic properties by redshifting the absorption spectra and deepening the lowest unoccupied molecular orbital energy levels, but also the molecular packing and thus thin‐film morphology. The PM6:ITC‐2Cl‐based device yields a significantly higher PCE (13.6%) with a lower Eloss (0.67 eV) than the ITCPTC‐based device (PCE of 12.3% with Eloss of 0.70 eV). More importantly, compared to the archetypal nonfullerene acceptors such as IT‐4F (PCE of 12.9% with Eloss of 0.73 eV) and IT‐4Cl (PCE of 12.7% with Eloss of 0.76 eV), the ITC‐2Cl‐based device shows a higher PCE and a lower Eloss. These results demonstrate that the chlorinated thiophene‐fused end group is a promising candidate for a high‐performance nonfullerene acceptors with low energy loss. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of 1D/2A type novel wide-bandgap terpolymer donors were synthesized. • Using a simple and low-cost electron-deficient building block DTCPz to develop terpolymers. • The hero PSC presents a particularly increased PCE of 17.8%, with ca. 11% of improvement from that of 16.0% for the parent PM6-based ones. • Our terpolymer strategy provides a positive effect on improving the thermal stability of the device. It had been commonly accepted in the organic photovoltaic (OPV) community that subtle variations in the molecular structure of active layer materials would cause profound impacts on their aggregating structure and blend morphology and therefore the performance of such polymer solar cells (PSCs). Herein, we employed an electron-deficient building block 3,6-dithiophenyl-2-carboxylate pyrazine (DTCPz) for constructing one series of promising donor terpolymers of PMZ1, PMZ2, and PMZ3, respectively, gaining their relatively lower-lying highest occupied molecular orbital (HOMO) energy levels, more closed π-π stacking and enhanced crystallinity in thin films, and lower miscibility with acceptor Y6, in comparison with their parent polymer counterpart (namely PM6). Reaching DTCPz moieties up to 20% (mol/mol%) in its terpolymer composition, the resulting polymer (PMZ2) achieved more favorable phase separation with improved exciton dissociation, and charge transport and extraction. As a result, an outstanding fill factor of 77.2% and a promising power conversion efficiency of 17.8 % was achieved. Moreover, the corresponding device shows better thermal stability over the PM6-based one. This work suggests a facile method for significantly improving the thin film morphology of the active-layer materials via fine-tuning the chemical structure of electron-deficient units on the backbone of the wide bandgap donor polymer, therefore achieving enhanced photovoltaic performance and thermal stability for practical applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Derived from Y6, BTSi-4F has a novel bulky siloxane-terminated group as side-chains. • BTSi-4F exhibits a better solubility and up-shifted LUMO energy level. • BTSi-4F shows a more ordered molecular packing, and higher electron-mobility. • The PM6:BTSi-4F film shows a better blend miscibility than PM6:Y6 film. • The PCE of the OSCs was improved from 13.0% to 16.6% upon modification. As one of the simple but most effective molecular design strategies, side-chain engineering has been widely employed to modify the photoelectric properties of active layer materials for boosting the photovoltaic performance of organic solar cells (OSCs). Herein, a functionalized small molecule acceptor (SMA) named BTSi-4F with a bulky siloxane-terminated solubilizing group as side-chains, derived from a classical SMA of Y6, was designed and synthesized. The results demonstrate that the introduction of siloxane-functional terminated groups into SMA not only affects the optical absorption and molecular energy levels, but also regulates the miscibility between the polymer donor and SMA. Compared to the original Y6, BTSi-4F exhibits a better solubility, upshifted lowest unoccupied molecular orbital (LUMO) energy level, more ordered molecular packing, and higher electron-mobility. Matched with a wide bandgap polymer donor PM6, the chlorobenzene-processed OSCs based on PM6:BTSi-4F achieved a superior power conversion efficiency (PCE) of 16.6% with both high open-circuit voltage (V oc) of 0.90 V and high fill factor (FF) of 0.77, while the devices based on PM6:Y6 obtained a much lower PCE of 13.0% with a V oc of 0.81 V and FF of 0.69 under the same conditions. This work offers a promising molecular design strategy of siloxane-terminated side chain engineering to develop high-performance SMAs for efficient OSCs. [ABSTRACT FROM AUTHOR]

• A terpolymer PF1 was developed by incorporating fluorinated BFT into PM6 backbone. • Introducting BFT can effectively tailor the molecular aggregation properties. • The PF1:Y6-based OSCs achieved a power conversion efficiency of up to 17.3%. Regulating molecular aggregation state via chemical modification of photovoltaic materials to optimize the blend morphology is an effective and challenging strategy to improve the photovoltaic performance of organic solar cells (OSCs). In this work, we demonstrate a random terpolymerization strategy by incorporating 1,3-bis(5-bromo-4-fluorothiophen-2-yl)-5,7-bis(2-ethylhexyl)-4H,8H-benzo[1,2-c:4,5-c']bisthiophene-4,8-dione (BFT, 30 mol%) unit with fluorinated π-bridges into the molecular backbone of PM6 and develop a terpolymer PF1. Benefiting from the strong electronegativity of fluorine atom and noncovalent interaction of F---S, the energy levels, molecular ordering, and aggregation properties of the polymer donors are precisely regulated. Notably, in the active layer film based on PF1: Y6, the π-π stacking distance can reduce to 3.51 Å, which is significantly smaller than that of PM6:Y6 (3.65 Å) and boosts the effective exciton dissociation and charge transport, thereby effectively optimize the photovoltaic properties of the related devices. As a result, the PF1:Y6-based OSCs achieved a power conversion efficiency (PCE) of up to 17.3%, which is much higher than that of the controlled OSCs based on PM6:Y6 (PCE = 16.2%). These results demonstrate high-efficiency OSCs enabled by regulating molecular aggregation via terpolymerization strategy. [ABSTRACT FROM AUTHOR]

To further elevate the power conversion efficiency (PCE) of organic solar cells (OSCs), ternary strategy is one of the most efficient methods via simply incorporating a suitable third component. Here, a nonfullerene small molecule acceptor MOITIC was incorporated into the state-of-art PM6:Y6 binary system to further enhance the photovoltaic performance. Detailed investigation revealed that MOITIC exhibited a good miscibility and compatibility with Y6, forming alloy-like acceptors in the ternary blends. The alloy-like phase promoted the phase separation and optimized the morphology of ternary blend, which afforded higher and more balanced carrier mobility and reduced charge recombination in devices. Moreover, the larger energy offset between PM6 and MOITIC:Y6 acceptor alloy is beneficial to enhance open-circuit voltage (V oc) of corresponding devices. As a consequence, the optimized ternary OSC (PM6:Y6:MOITIC = 1:1:0.1) showed a significantly increased PCE of 17.1% with simultaneously enhanced V oc of 0.882 V, short-circuit current density (J sc) of 25.6 mA cm−2, and fill factor (FF) of 75.7%, which has about 9% enhancement compared to the control binary PM6:Y6 (15.7%). In addition, the optimized ternary device exhibited better stability. This work indicates that ternary strategy via combining two compatible small molecule acceptors is effective to simultaneously improve the efficiency and stability of OSCs. Ternary strategy is one of the most efficient approaches to further improve performance of OSCs via simply incorporating a suitable third component. Here, a compatible dual-acceptors strategy was used to construct efficient alloy-like TOSCs. The alloy dual-acceptors promoted charge transport and fixed the nanoscale morphology of ternary active layers, as a consequence, both enhanced efficiency and stability were obtained in the optimized ternary device. [Display omitted] • A nonfullerene acceptor, MOITIC, was incorporated into the PM6:Y6 system to construct efficient ternary organic solar cells. • Ternary devices achieved a high efficiency of 17.1% with simultaneously improved three photovoltaic paraments. • The stability of the optimized ternary device was synergistically improved by the incorporation of MOITIC. [ABSTRACT FROM AUTHOR]

Ternary blending is one of the effective strategies to modulate the blend film morphology for achieving high efficiency organic solar cells (OSCs). In this work, high-performance ternary OSCs are fabricated by introducing a non-fullerene acceptor, namely IDTP-4F into the PM6:Y6 binary system to enhance the device performance. Detailed investigations indicate that IDTP-4F can form an alloy phase with Y6, resulting in the optimized morphology, which can facilitate the charge transport and reduce recombination, leading to enhanced open-circuit voltage (V oc) and fill factor (FF) simultaneously. Consequently, the optimized ternary OSCs exhibit an excellent power conversion efficiency (PCE) of 17.1%, which is much higher than that of PM6:Y6 binary OSCs (15.9%). These results indicate that combining two compatible non-fullerene acceptors is an effective strategy to fabricate high efficiency ternary OSCs. • High-performance ternary OSCs are fabricated by introducing a non-fullerene acceptor into PM6:Y6 binary system. • IDTP-4F can form an alloy phase with Y6, which results in the enhanced open-circuit voltage (V oc) in ternary OSCs. • The optimized ternary OSCs exhibit an excellent PCE of 17.1%, which is much higher than that of PM6:Y6 binary OSCs (15.9%). [ABSTRACT FROM AUTHOR]