Although organic photovoltaic (OPV) cells have many advantages, their performance still lags far behind that of other photovoltaic platforms. A fundamental reason for their low performance is the low charge mobility of organic materials, leading to a limit on the active-layer thickness and efficient light absorption. In this work, guided by a semi-empirical model analysis and using the tandem cell strategy to overcome such issues, and taking advantage of the high diversity and easily tunable band structure of organic materials, a record and certified 17.29% power conversion efficiency for a two-terminal monolithic solution-processed tandem OPV is achieved.

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Highlights Various morphological structures in pressure sensors with the resulting advanced sensing properties are reviewed comprehensively. Relevant manufacturing techniques and intelligent applications of pressure sensors are summarized in a complete and interesting way. Future challenges and perspectives of flexible pressure sensors are critically discussed.

better organic active layer materials, such as those star materials of P3HT (2005 by Kim et al.), [2c] DR3TBDTT (2013 by Chen et al.), [2e] ITIC (2015 by Zhan et al.), [2f ] PM6 (2015 by Hou et al.), [2g] Y6 (2019 by Zou et al.), [2h] D18 (2018 by Ding et al.). [2i] Especially in 2019, the rapidly developing OSCs stepped into a new era of PCE exceeding 15% due to the emergence of a super-star acceptor Y6. [2g] As we all known that two determining factors for PCE of OSCs are the active layer materials and its morphology. Therefore, there have been main two approaches for higher performance, one is to get better molecules, and the latter one is to achieve better morphology. While we are always exploring more efficient active layer materials, the journey has been long and challenging. Therefore, it would be much easier to tune the morphology for better performance using some existing materials to achieve their best intrinsic performance. Up to now, tremendous efforts in tuning morphology have been made in the Y6 analogs-based OSCs, such as more suitable coating solvent, [3] solvent [4] or low boiling point solid additives, [5] post treatments of thermal or solvent annealing, [6] rendering the PCE over 18%. [7] In spite of the impressive PCE achieved, the continuously increasing performance of Y6 analogs-based OSCs indicates that the intrinsic best performance might not have been achieved.The above strategies of morphology regulation, such as more suitable coating solvent, solvent or low boiling point solid additives, post treatments of thermal or solvent annealing, can adapt a favorable morphology upon the quick solvent volatile process or post-treatment process by controlling the crystallization and phase separation process. In addition, a multicomponent strategy, which introduces a guest component into the host systems in OSCs, has been proved as an effective way to further improve the device performance recently. [7a,8] The application of a multicomponent strategy can break the limits of light absorption of the existing host systems, optimize the morphology and energy level alignment for the active layer, and thus improve the efficiency of OSC devices. Thus, a feasible multicomponent strategy based on a state-of-the-art system is expected to guide superior device performances. In the past decade, the numerous oligomer-like donors-based organic A wide bandgap oligomer-like donor CNS-6-8 is synthesized and incorporated into the host PM6:Y6:PC 71 BM system to tune the morphology of the active layer for better device performance. Due to the good miscibility of CNS-6-8 with both host donor (PM6) and acceptors (Y6 and PC 71 BM), an optimized morphology is achieved with the appropriate phase separation size and enhanced crystallinity, which ultimately leads to more efficient exciton dissociation, charge transport, and lower nonradiative energy loss. As a result, the quaternary device achieves an improved efficiency of 18.07%, with a simultaneously increased open circuit voltage of 0.868 V, fill factor of 78....

Both the efficiency and stability of low-cost organic solar cells are central components for meeting the requirements of commercialization for organic photovoltaics (OPV). Furthermore, the relationship between the chemical structure of an active material and morphology and its effects on efficiency and stability is still largely undetermined. Additionally, both the kinetic and thermodynamic morphology states of an active layer can have a huge impact on efficiency and stability, even when the chemical structures of materials applied in the active layer are especially the same or similar. Here, using two series of acceptor–donor–acceptor (A–D–A)-type small-molecule acceptors (SMAs) with similar backbone structures, we demonstrate the relevance of fine-tuned chemical structures with their solution and solid-state properties, further leading to significantly different behavior in terms of both device efficiency and stability. This is also partially due to the different morphology states caused by such fine chemical structure tuning. Our results indicate that a delicate balance of molecular aggregation and ordered stacking morphology is required to achieve and lead to high efficiency and stability. Thus, among the two series of molecules, UF-EH-2F, with both optimal length and steric hindrance of side chains, achieves the preponderant morphology in its corresponding device, where its morphologies “efficient state” and “stable state” are almost overlapped, and thus lead to both the highest efficiency (power conversion efficiency, PCE = 13.56%) and the best stability. Our results indicate that it is highly possible to achieve the morphology state required for both high efficiency and stability simultaneously by fine-tuning the chemical structure of active materials for organic solar cells.