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In series‐connected tandem organic solar cells (TOSCs), various light‐harvesting molecules with complementary absorptions are explored with the aim of collaboratively utilizing solar light to the maximum extent. In sharp contrast to the small molecular acceptors that possessing almost the successively tunable bandgaps, high‐performance wide‐bandgap (WBG) polymer donors in TOSCs are quite scarce, with only PM6 (optical bandgaps, Egopt = 1.80 eV) and D18 (Egopt = 1.98 eV) being widely used. Herein, to develop WBG polymer donors with large open‐circuit voltages (VOC) and high‐energy photon absorption, two pyrazinyl polymer donors, PPy1 and PPy2, are synthesized with branched 2‐butyloctyl and n‐dodecyl chains on polymeric backbones, respectively, demonstrating the downshifted highest occupied molecular orbital energy levels of ≈−5.60 eV and thus afford Egopt over 2.0 eV. Consequently, when blending with a WBG acceptor F‐ThCl, PPy2:F‐ThCl‐based devices exhibit a higher power conversion efficiency (PCE) of 14.50% and fill factor of 77.66%. In light of its large VOC of 1.07 V, TOSCs based on PPy2 are further fabricated and exhibit an impressive PCE of 19.35% by using a narrow bandgap blend of PM6:CH1007:F‐2F as a rear cell. This work demonstrates the great potential of pyrazine units in constructing WBG polymer donors for achieving record‐breaking TOSCs. [ABSTRACT FROM AUTHOR]

Highlights: Additive-assisted layer-by-layer (LBL) deposition enables organic solar cells to achieve an unprecedented power conversion efficiency of 20.8%, the highest efficiency to date. The gradient fibrillar morphology enabled by additive-assisted LBL processing promotes the formation of bulk p-i-n structure, improving exciton and carrier diffusion, and reducing recombination losses. The wrinkle pattern morphology achieved by additive-assisted LBL processing is constructed to enhance the light capture capability. Recently published in Joule, Feng Liu and colleagues from Shanghai Jiaotong University reported a record-breaking 20.8% power conversion efficiency in organic solar cells (OSCs) with an interpenetrating fibril network active layer morphology, featuring a bulk p-i-n structure and proper vertical segregation achieved through additive-assisted layer-by-layer deposition. This optimized hierarchical gradient fibrillar morphology and optical management synergistically facilitates exciton diffusion, reduces recombination losses, and enhances light capture capability. This approach not only offers a solution to achieving high-efficiency devices but also demonstrates the potential for commercial applications of OSCs. [ABSTRACT FROM AUTHOR]

Nonlinear activation functions play a crucial role in artificial neural networks. However, digital implementations of sigmoidal functions, the commonly used activation functions, are facing challenges related to energy consumption and area requirements. To address these issues, we develop a proof-of-concept computing system that utilizes magnetic tunnel junctions as the key element for implementing sigmoidal activation functions. Using this system, we train a neural network for speech separation. When compared to state-of-the-art digital implementations, our scalable circuit has the potential to consume up to 383 times less energy and occupy 7354 times smaller area. These results pave the way for more efficient computing systems in the future. [ABSTRACT FROM AUTHOR]

Optical communication is a particularly compelling technology for tackling the speed and capacity bottlenecks in data communication in modern society. Currently, the silicon photodetector plays a dominant role in high-speed optical communication across the visible-near-infrared spectrum. However, its intrinsic rigid structure, high working bias and low responsivity essentially limit its application in next-generation flexible optoelectronic devices. Herein, we report a narrow-bandgap non-fullerene acceptor (NFA) with a remarkable π-extension in the direction of both central and end units (CH17) with respect to the Y6 series, which demonstrates a more effective and compact 3D molecular packing, leading to lower trap states and energetic disorders in the photoactive film. Consequently, the optimized solution-processed organic photodetector (OPD) with CH17 exhibits a remarkable response time of 91 ns (λ = 880 nm) due to the high charge mobility and low parasitic capacitance, exceeding the values of most commercial Si photodiodes and all NFA-based OPDs operating in self-powered mode. More significantly, the flexible OPD exhibits negligible performance attenuation (<1%) after bending for 500 cycles, and maintains 96% of its initial performance even after 550 h of indoor exposure. Furthermore, the high-speed OPD demonstrates a high data transmission rate of 80 MHz with a bit error rate of 3.5 |$ \times $| 10−4, meaning it has great potential in next-generation high-speed flexible optical communication systems. [ABSTRACT FROM AUTHOR]

High-speed and sensitivity solution-processed organic photodetectors (OPDs) have drawn great attention for their promising applications in next-generation optoelectronics, including optical communication, imaging, autonomous driving, and military security. However, current OPDs commonly suffer from slow response speed due to low charge mobility, significantly hindering their applications in optical wireless communication. Herein, a pair of nonfullerene acceptors (NFAs), featuring a prominent π extension in the central units with respect to Y6, are synthesized with the same backbone but different halogenations in end cap groups, namely, CH-4Cl and CH-4F. The OPD based on CH-4Cl exhibits a remarkably short response time of 270 ns (λ = 850 nm) and detectivity of >1013 Jones in a self-powered mode, improving 34% and 500% compared to the values of OPD with CH-4F NFA, respectively, which ranks the highest speed among self-powered solution-processed binary OPD-based on NFAs. This outstanding performance is attributed to the low trap states and energetic disorders of OPDs with CH-4Cl. Furthermore, the high-speed OPD demonstrates a promising application in high-speed optical wireless communication. [ABSTRACT FROM AUTHOR]

The flexible near‐infrared (NIR) organic photodetector is an essential prerequisite for the next‐generation visual system for accurate information identification. However, prevailing limitations in NIR organic photodetectors, including high noise, weak responsivity, and low detectivity, directly impede the translation to practical applications. Herein, ultranarrow bandgap acceptors, featuring a 2D highly electron‐donating central core (DTPC), named as YZ and YZ1, are designed and synthesized for NIR organic photodetectors. It is found that the introduction of highly rigid DTPC effectively reduces energetic disorder in active films. Moreover, extending the end conjugation not only broadens the absorption spectrum but also diminishes trap states and improves charge transport. Consequently, the YZ1‐based organic photodetector exhibits an impressive detection range from 300 to 1050 nm with a high responsivity of 0.27 A W−1 at 1000 nm and specific detectivity of 9.24 × 1013 Jones, comparable to commercial silicon photodiodes. Inspired by biological eyes, large‐area parallelly independent photodetector arrays (2000 pixels) for an artificial vision system are fabricated, which enables a clear matter identification in the NIR region. These findings and results simultaneously provide critical insights into molecular design and bridge the gap between material science and device engineering, accelerating the application of NIR organic photodetectors in next‐generation wearable optoelectronics. [ABSTRACT FROM AUTHOR]

Conventional halogenations such as fluorination, chlorination and bromination on non-fullerene acceptors (NFAs) generally contribute to a dramatic improvement in overall photovoltaic performance of organic solar cells (OSCs). Despite the potentially enhanced intermolecular interaction caused by iodine atoms with increased polarizability, iodinated NFAs are quite rare due to the high-reactive activity of iodine. Here, an iodinated acceptor (CH45) is constructed, rendering a first-class efficiency of 18.15% for OSCs without any extra post-treatments, attributed to the enlarged molecular polarizability and dielectric constant, and further reduced exciton binding energy of CH45. Moreover, the working mechanism of 1-chloronaphthalene additive to greatly improve fill factors of CH45-based OSCs is also revealed at single-crystal levels. By successfully establishing such a rarely iodinated but high-performance molecular platform, more delicately iodinated light-harvesting molecules with unexpected properties (such as significantly enhanced intermolecular non-covalent actions) will be inspired to further achieve high-efficiency OSCs without tedious post-treatments. [ABSTRACT FROM AUTHOR]