A non-fullerene acceptor enables efficient P3HT-based organic solar cells with small voltage loss and thickness insensitivity

Poly(3-hexylthiophene)(P3HT) is a low-cost polymer donor for organic solar cells (OSCs). However, the P3HT-based OSCs usually give low power conversion efficiencies (PCEs) due to the wide bandgap and the high-lying energy levels of P3HT. To solve this problem, in this work, we design and synthesize a new A-D-A type non-fullerene acceptor, DFPCBR, which owns an electron-donating (D) core constructed by linking a 2,5-difluorobenzene ring with two cyclopentadithiophene moieties, and two electron-accepting (A) end-groups of benzo[c][1,2,5]thiadiazole connected with 3-ethyl-2-thioxothiazolidin-4-one. Because of the strong electron-donating ability and large conjugation effect of D core, DFPCBR shows appropriate energy levels and a narrow bandgap matching well with those of P3HT. Therefore, with P3HT as the donor and DFPCBR as the acceptor, the OSCs possess broad absorption range from 350 nm to 780 nm and the reduced energy loss (Eloss) of 0.79 eV (compared with ~1.40 eV for the P3HT:PC61BM device), providing a good PCE of 5.34% with a high open-circuit voltage (VOC) of 0.80 V. Besides, we observe that the photovoltaic performances of these devices are insensitive to the thickness of the active layers:even if the active layer is as thick as 320 nm,~80%of the best PCE is maintained, which is rarely reported for fullerene-free P3HT-based OSCs, suggesting that DFPCBR has the potential application in commercial OSCs in the future.

In-depth investigation and applications of novel silicon photonics microstructures supporting optical vorticity and waveguiding for ultranarrowband near-infrared perfect absorption

We propose a novel concept of designing silicon photonics metamaterials for perfect near-infrared light absorption.The study's emphasis is an in-depth investigation of various physical mechanisms behind the^100%ultranarrowband record peak absorptance of the designed structures,comprising an ultrathin silicon absorber.The electromagnetic power transport,described by the Poynting vector,is innovatively explored,which shows combined vortex and crossed-junction two-dimensional waveguide-like flows as outcomes of optical field singularities.These flows,though peculiar for each of the designed structures,turn out to be key factors of the perfect resonant optical absorption.The electromagnetic fields show tight two-dimensional confinement:a sharp vertical confinement of the resonant-cavity type combined with a lateral metasurface supported confinement.The siliconabsorbing layer and its oxide environment are confined between two subwavelength metasurfaces such that the entire design is well compatible with silicon-on-insulator microelectronics.The design concept and its outcomes meet the extensive challenges of ultrathin absorbers for minimum noise and an ultra-narrowband absorptance spectrum,while maintaining an overall very thin structure for planar integration.With these materials and such objectives,the proposed designs seem essential,as standard approaches fail,mainly due to a very low silicon absorption coefficient over the near-infrared range.Tolerance tests for fabrication errors show fair tolerability while maintaining a high absorptance peak,along with a controllable deviation off the central-design wavelength.Various applications are suggested and analyzed,which include but are not limited to:efficient photodetectors for focal plane array and on-chip integrated silicon photonics,high-precision spectroscopic chemical and angular-position sensing,and wavelength-division multiplexing.