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M‐series molecules are one kind of promising acceptor‐donor‐acceptor (A‐D‐A)‐type acceptors for constructing high‐performance organic solar cells (OSCs). However, their power conversion efficiencies (PCEs) are lagging behind that of current state‐of‐the‐art OSCs, limited by the relatively low fill factor (FF) and photocurrent. Herein, combined strategies of layer‐by‐layer (LBL) deposition and interface engineering are conducted to systematically improve light utilization and thus PCEs for M36‐based OSCs. Through choosing a proper processing solvent, a PCE of 17.3% with an FF of 77.9% is achieved for the resulting LBL devices, much higher than those (15.9%/74.0%) from the blend‐casting devices. The improvement is assigned to the favorable morphological evolution that facilitates carrier generation and transport as well as reduces charge recombination. More importantly, light‐harvesting of the active layers can be enhanced upon employing a self‐assembled monolayer of (2‐(9H‐carbazol‐9‐yl)ethyl)phosphonic acid (2PACz) instead of the widely used PEDOT:PSS as the hole‐selecting layer, due to the decreased parasitic absorption of the former. Consequently, 2PACz‐based LBL devices exhibit significantly increased photocurrent, affording a PCE up to 18.2%, which is the highest among the reported A‐D‐A‐type acceptor‐based OSCs. These results deliver important strategies to enhance the performance of OSCs and thus highlight the great potential of M‐series acceptors for practical applications. [ABSTRACT FROM AUTHOR]

Compared to the polymer donor materials with symmetric structures, those with asymmetric structures usually have an increased dipole moment and therefore an enhanced intermolecular interaction which may eventually improve their photovoltaic performance. In this work, two novel wide bandgap donor–acceptor alternating copolymers (POS and PSS) are designed and synthesized by polymerizing benzodithiophene-derived electron-rich units (D) containing symmetric and asymmetric side chains with an electron-deficient unit (A) of 1,3-bis(2-ethylhexyl)-5,7-bis(5-(trimethylstannyl)thiophen-2-yl)benzo[1,2-c:4,5-c′]dithiophene-4,8-dione, respectively. Although both two copolymers possess large optical bandgaps, POS with asymmetric side chains exhibits a smaller π–π stacking distance and a deeper energy level of the highest occupied molecular orbital in comparison with PSS. When blended with the benchmark acceptor of Y6, the best-performing POS:Y6-based device exhibits a higher PCE of 15.02% with an enhanced VOC of 0.820 V, a JSC of 26.86 mA cm−2, and a higher fill factor (FF) of 68.20% in comparison with the PSS:Y6-based OSC which shows a PCE of 13.38% with a VOC of 0.800 V, a JSC of 27.26 mA cm−2, and an FF of 61.06%. The enhanced PCE for the POS:Y6-based device can be attributed to the higher charge carrier mobility, more balanced charge transport, and less charge recombination. This study indicates that the asymmetric side chains on the electron-donating benzodithiophene unit can greatly affect the photovoltaic performance of the resulting D–A copolymers. [ABSTRACT FROM AUTHOR]

Y6, as a state‐of‐the‐art nonfullerene acceptor (NFA), is extensively optimized by modifying its side chains and terminal groups. However, the conformation effects on molecular properties and photovoltaic performance of Y6 and its derivatives have not yet been systematically studied. Herein, three Y6 analogs, namely, BP4T‐4F, BP5T‐4F, and ABP4T‐4F, are designed and synthesized. Owing to the asymmetric molecular design strategies, three representative molecular conformations for Y6‐type NFAs are obtained through regulating the lateral thiophene orientation of the fused core. It is found that conformation adjustment imposes comprehensive effects on the molecular properties in neat and blend films of these NFAs. As a result, organic solar cells (OSCs) fabricated with PM6:BP4T‐4F, PM6:BP5T‐4F, and PM6:ABP4T‐4F show high power conversion efficiency of 17.1%, 16.7%, and 15.2%, respectively. Interestingly, these NFAs with different conformations also show reduced energy loss (Eloss) in devices via gradually suppressed nonradiative Eloss. Moreover, by employing a selenium‐containing analog, CH1007, as the complementary third component, ternary OSCs based on PM6:BP5T‐4F:CH1007 (1:1.02:0.18) achieve a 17.2% efficiency. This work helps shed light on engineering the molecular conformation of NFAs to achieve high efficiency OSCs with reduced voltage loss. [ABSTRACT FROM AUTHOR]

The development of high‐performance donor polymers is important for obtaining high power conversion efficiencies (PCEs) of non‐fullerene polymer solar cells (PSCs). Currently, most high‐efficiency PSCs are fabricated with benzo[1,2‐b:4,5‐b′]dithiophene (BDT)‐based conjugated polymers. The photovoltaic performance of benzo[1,2‐b:4,5‐b′]difuran (BDF)‐based copolymers has lagged far behind that of BDT‐based counterparts. In this study, a novel BDF‐based copolymer L2 is designed and synthesized, in which BDF and benzotriazole (BTz) building blocks have been used as the electron‐sufficient and deficient units, respectively. When blending with a non‐fullerene small molecule acceptor (SMA), TTPT‐T‐4F, the L2‐based device exhibits a remarkably high PCE of 14.0%, which is higher than that of the device fabricated by its analogue BDT copolymer (12.72%). Moreover, PSCs based on the L2:TTPT‐T‐4F blend demonstrate excellent ambient stability with 92% of its original PCE remaining after storage in air for 1800 h. Thus, BDF is a promising electron‐donating unit, and the BDF‐based copolymers can be competitive or even surpass the performance of BDT‐based counterparts. [ABSTRACT FROM AUTHOR]

Power conversion efficiencies (PCEs) of the methylammonium‐free (MA‐free) perovskite solar cells (PSCs) are constantly lagging behind those of the most extensively researched triple cation mixed PSCs due to their subpar perovskite films. Here, two guanidine‐based passivation agents are proposed, that are, sulfaguanidine (S‐Gua) and 1‐acetylguanidine (A‐Gua) that can be applied to optimize the film quality of MA‐free perovskite for minimizing the efficiency discrepancy between the two types of PSCs. Through strong coordination with Pb2+ and hydrogen bonding with formamidinium (FA+), the two passivation additives can reduce bulk defects and suppress non‐radiative recombination, which in turn enhance the charge extraction and transfer efficiency. Consequently, the S‐Gua‐ and A‐Gua‐treated devices achieve PCEs of 24.34% and 23.77%, respectively. Both PCEs are greater than that of the control device (23.03%), and the 24.34% PCE is comparable with that of the best MA‐free inverted PSCs with narrower bandgaps. Moreover, the S‐Gua‐treated devices maintain 89.3% and 82.0% of their initial PCEs after aging for 800 h and heating (85 °C) for 340 h in ambient air without any encapsulation, respectively. This work offers comprehensive insights into the use of guanidine‐based additives to achieve high‐quality perovskite films and subsequently state‐of‐the‐art MA‐free PSCs. [ABSTRACT FROM AUTHOR]

The ternary structure that combines fullerene and nonfullerene acceptors in a photoactive layer is demonstrated as an effective approach for boosting the power conversion efficiencies (PCEs) of organic solar cells (OSCs). Here, highly efficient ternary OSCs comprising a wide‐bandgap polymer donor (PBT1‐C), a narrow‐bandgap nonfullerene acceptor (IT‐2F), and a typical fullerene derivative (PC71BM) are reported. It is found that the addition of PC71BM into the PBT1‐C:IT‐2F blend not only increases the device efficiency up to 12.2%, but also improves the ambient stability of the OSCs. Detailed investigations indicate that the improvement in photovoltaic performance benefits from synergistic effects of increased photon‐harvesting, enhanced charge separation and transport, suppressed trap‐assisted recombination, and optimized film morphology. Moreover, it is noticed that such a ternary system exhibits excellent tolerance to the PC71BM component, for which PCEs over 11.2% can be maintained throughout the whole blend ratios, higher than that (11.0%) of PBT1‐C:IT‐2F binary reference device. Ternary organic solar cells with improved power conversion efficiency (PCE) and ambient stability are developed by combining a nonfullerene acceptor and a fullerene acceptor. Such a ternary system is insensitive to the content of the third component, and PCEs over 11.2% can be maintained throughout the whole blend ratios, higher than that (11.0%) of the binary reference device. [ABSTRACT FROM AUTHOR]

Indacenodithiophene (IDT) has been widely used as the central core to design high‐performance acceptor‐donor‐acceptor (A‐D‐A)‐type non‐fullerene acceptors (NFAs). NFAs based on five‐, six‐, seven‐, and nine‐membered IDT have been successfully prepared. However, less research attention has been paid to the eight‐membered IDT derivative. In this study, a novel asymmetric TTPTTT building block as an eight‐membered IDT unit are designed and synthesized. The effect of nonfluorinated, monofluorinated, and difluorinated end‐capping groups on the photovoltaic performance of TTPTTT‐based NFAs are specifically investigated. By blending with the polymer donor PBT1‐C, organic solar cells (OSCs) based on TTPTTT‐IC, TTPTTT‐2F, and TTPTTT‐4F exhibited power conversion efficiencies (PCEs) of 7.91, 11.52, and 12.05%, respectively. Our results indicate that the asymmetric TTPTTT building block as an eight‐membered IDT derivative is a promising central core unit for designing high‐performance A‐D‐A type NFAs. A novel TTPTTT building block as an eight‐membered indacanodithiophene derivative is developed. The effect of nonfluorinated, momofluorinated, and difluorinated end‐capping group on photovoltaic performance of asymmtry TTPTTT non‐fullerene acceptors (NFAs) is investigated. As a result, organic solar cells based on TTPTTT‐4F exhibit a high efficiency of 12.05%, indicating that the asymmetric TTPTTT unit is a promising central core unit for designing efficient A‐D‐A type NFAs. [ABSTRACT FROM AUTHOR]