Thermally Stable D2h Symmetric Donor-π-Donor Porphyrins as Hole-Transporting Materials for Perovskite Solar Cells.

A series of new D2h symmetric porphyrins (MDA4, MTA4, and MDA8) with donor-π-donor structures have been synthesized as the hole-transporting materials for perovskite solar cells (PSCs). The novel porphyrin molecules feature a D2h symmetrically substituted ZnII porphyrin core and two kinds of donor systems (diarylamine (DAA) and triarylamine (TAA)), which can regulate energy level, increase thermal stability, solubility, and hydrophobicity via long alkoxyl chains. PSC devices based on MDA4 as the HTM showed impressive power-conversion efficiency (PCE) of 22.67 % under AM1.5G solar illumination. Notably, the device was sent for certification, and a PCE of 22.19 % was reported, representing the highest PCE from porphyrin-based HTMs. Furthermore, the MDA4-based PSCs showed excellent thermal stability under 60 °C and RH 60 % and preserved 88 % of initial performance after 360 hours. The strategy opens a new avenue for developing efficient and stable porphyrin HTMs for PSCs.

Uniform Luminous Perovskite Nanofibers with Color-Tunability and Improved Stability Prepared by One-Step Core/Shell Electrospinning.

A one-step core/shell electrospinning technique is exploited to fabricate uniform luminous perovskite-based nanofibers, wherein the perovskite and the polymer are respectively employed in the core and the outer shell. Such a coaxial electrospinning technique enables the in situ formation of perovskite nanocrystals, exempting the needs of presynthesis of perovskite quantum dots or post-treatments. It is demonstrated that not only the luminous electrospun nanofibers can possess color-tunability by simply tuning the perovskite composition, but also the grain size of the formed perovskite nanocrystals is largely affected by the perovskite precursor stoichiometry and the polymer solution concentration. Consequently, the optimized perovskite electrospun nanofiber yields a high photoluminescence quantum yield of 30.9%, significantly surpassing the value of its thin-film counterpart. Moreover, owing to the hydrophobic characteristic of shell polymer, the prepared perovskite nanofiber is endowed with a high resistance to air and water. Its photoluminescence intensity remains constant while stored under ambient environment with a relative humidity of 85% over a month and retains intensity higher than 50% of its initial intensity while immersed in water for 48 h. More intriguingly, a white light-emitting perovskite-based nanofiber is successfully fabricated by pairing the orange light-emitting compositional perovskite with a blue light-emitting conjugated polymer.

Stretchable Fluorescent Polyfluorene/Acrylonitrile Butadiene Rubber Blend Electrospun Fibers through Physical Interaction and Geometrical Confinement.

Stretchable light-emitting polymers are important for wearable electronics; however, the development of intrinsic stretchable light-emitting materials with great performance under large applied strain is the most critical challenge. Herein, this study demonstrates the fabrication of stretchable fluorescent poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl-fluorene)]/acrylonitrile butadiene rubber (PFN/NBR) blend nanofibers using the uniaxial electrospinning technique. The physical interaction of PFN with NBR and the geometrical confinement of nanofibers are employed to reduce PFN aggregation, leading to the high photoluminescence quantum yield of 35.7%. Such fiber mat film shows stable blue emission at the 50% strain for 200 stretching/release cycles, which has potential applications in smart textiles.

Recent progress in self-healable energy harvesting and storage devices - a future direction for reliable and safe electronics.

Electronic devices with multiple features bring in comfort to the way we live. However, repeated use causes physical as well as chemical degradation reducing their lifetime. The self-healing ability is the most crucial property of natural systems for survival in unexpected situations and variable environments. However, this self-repair property is not possessed by the conventional electronic devices designed today. To expand their lifetime and make them reliable by restoring their mechanical, functional, and electrical properties, self-healing materials are a great go-to option to create robust devices. In this review the intriguing self-healing polymers and fascinating mechanism of self-healable energy harvesting devices such as triboelectric nanogenerators (TENG) and storage devices like supercapacitors and batteries from the aspect of electrodes and electrolytes in the past five years are reviewed. The current challenges, strategies, and perspectives for a smart and sustainable future are also discussed.

Generation of Long-Lived Excitons in Room-Temperature Phosphorescence 2D Organic and Inorganic Hybrid Perovskites for Ultrafast and Low Power-Consumption Nonvolatile Photomemory.

Room-temperature phosphorescence (RTP) two-dimensional (2D) organic-inorganic hybrid perovskites (OIHPs) that possess superior stability and efficient triplet energy transfer between inorganic parts and organic cations have been seen as promising materials in optoelectronic devices. However, the development of RTP 2D OIHP-based photomemory has not been explored yet. In this work, the spatially addressable RTP 2D OIHPs-based nonvolatile flash photomemory is first investigated to explore the function of triplet excitons in elevating the performance of photomemory. Thanks to the triplet excitons generated in RTP 2D OIHP, extremely low photo-programming time of 0.7 ms, multilevel behavior of minimum 7 bits (128 levels), remarkable photoresponsivity of 19.10 AW-1 and significantly low power consumption of 6.79 × 10-8 J per bit can be achieved. The current study provides a new prospective in understanding triplet excitons function in nonvolatile photomemory.

Stretchable and Ambient Stable Perovskite/Polymer Luminous Hybrid Nanofibers of Multicolor Fiber Mats and Their White LED Applications.

We report the fabrication and optical/mechanical properties of perovskite/thermoplastic polyurethane (TPU)-based multicolor luminescent core-shell nanofibers and their large-scale fiber mats. One-step coaxial perovskite/TPU nanofibers had a high photoluminescence quantum yield value exceeding 23.3%, surpassing that of its uniaxial counterpart, due to the homogeneous distribution of perovskite nanoparticles (NPs) by the confinement of the TPU shell. The fabricated core-shell nanofibers exhibited a high mechanical endurance owing to the well elastic properties of TPU and maintained the luminescence intensity even under a 100% stretched state after 1000 stretching-relaxing cycles. By taking advantage of the hydrophobic nature of TPU, the ambient and moisture stability of the fabricated fibers were enhanced up to 1 month. Besides, large-area stretchable nanofibers with a dimension of 15 cm × 30 cm exhibiting various visible-light emission peaks were fabricated by changing the composition of perovskite NPs. Moreover, a large-scale luminescent and stretchable fiber mat was successfully fabricated by electrospinning. Furthermore, the white-light emission from the fabricated fibers and mats was achieved by incorporating orange-light-emitting poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] into the TPU shell and coupling the turquoise blue-light-emitting perovskite NPs in the core site. Finally, the integrity of the perovskite-based TPU fibers was realized by fabricating a light-emitting diode (LED) device containing the orange-light-emitting fibers embedded in the polyfluorene emissive layer. This work demonstrated an effective way to prepare stable and stretchable luminous nanofibers and the integration of such nanofibers into LED devices, which could facilitate the future development of wearable electronic devices.

Solvent Effects on Morphology and Electrical Properties of Poly(3-hexylthiophene) Electrospun Nanofibers.

Herein, poly(3-hexylthiophene-2,5-diyl) (P3HT) nanofiber-based organic field-effect transistors were successfully prepared by coaxial electrospinning technique with P3HT as the core polymer and poly(methyl methacrylate) (PMMA) as the shell polymer, followed by extraction of PMMA. Three different solvents for the core polymer, including chloroform, chlorobenzene and 1,2,4-trichlorobenzene, were employed to manipulate the morphologies and electrical properties of P3HT electrospun nanofibers. Through the analyses from dynamic light scattering of P3HT solutions, polarized photoluminescence and X-ray diffraction pattern of P3HT electrospun nanofibers, it is revealed that the P3HT electrospun nanofiber prepared from the chloroform system displays a low crystallinity but highly oriented crystalline grains due to the dominant population of isolated-chain species in solution that greatly facilitates P3HT chain stretching during electrospinning. The resulting high charge-carrier mobility of 3.57 × 10-1 cm2·V-1·s-1 and decent mechanical deformation up to a strain of 80% make the P3HT electrospun nanofiber a promising means for fabricating stretchable optoelectronic devices.

Influence of polymeric electrets on the performance of derived hybrid perovskite-based photo-memory devices.

Organic-inorganic hybrid perovskite has become one of the most important photoactive materials owing to its intense light-harvesting property as well as its facile solution processability. Besides its photovoltaic applications, a novel photo-programmed transistor memory was recently developed based on the device architecture of a floating-gate transistor memory using a polymer/perovskite blend as the gate dielectric with the non-volatile memory characteristics of decent light response, applicable On/Off current ratio, and long retention time. In this study, we further clarify the influence of polymer matrix selection on the photo-response and memory properties of derived hybrid perovskite-based photo-memory devices. Four different host polymers, polystyrene (PS), poly(4-vinylphenol) (PVPh), poly(methyl methacrylate) (PMMA), and poly(methacrylic acid) (PMAA), were systematically investigated for comparison herein. This revealed that dissimilar chemical interactions existed between the host polymers and perovskite, resulting in the distinct memory behavior of the derived photo-memory devices, attributable to the different morphologies of the hybrid dielectric layers and the different sizes of the distributed perovskite nanoparticles (NPs). The photo-response behavior and the resultant On/Off current ratio increased as the size of the embedded perovskite NPs decreased, due to the enhanced photo-induced charge transfer across the dielectric/pentacene interface, benefiting from the better confinement effect of perovskite NPs in the polymer matrix. These results demonstrate the influence of perovskite NP aggregation at the dielectric/pentacene interface on the resultant memory behavior of the newly developed photo-memory device.

Realization of Intrinsically Stretchable Organic Solar Cells Enabled by Charge-Extraction Layer and Photoactive Material Engineering.

The rapid development of wearable electronic devices has prompted a strong demand to develop stretchable organic solar cells (OSCs) to serve as the advanced powering systems. However, to realize an intrinsically stretchable OSC is challenging because it requires all the constituent layers to possess certain elastic properties. It thus necessitates a combined engineering of charge-transporting layers and photoactive materials. Herein, we first describe a stretchable electron-extraction layer using a blend of poly[(9,9-bis(3'-( N, N-dimethylamino)propyl)-2,7-fluorene)- alt-2,7-(9,9-dioctylfluorene)] (PFN) and nitrile butadiene rubber (NBR, Nipol 1072). This hybrid PFN/NBR layer exhibits a much lower Derjaguin-Muller-Toporov modulus (0.45 GPa) than the value (1.25 GPa) of the pristine PFN and could withstand a high strain (60% strain) without showing any cracks. Moreover, besides enriching the stretchability of PFN, the terminal carboxyl groups of NBR can ionize PFN to promote its solution-processability in polar solvents and to ensure the interfacial dipole formation at the corresponding interface in the device, as evidenced by the Fourier transform infrared and ultraviolet photoelectron spectroscopy analyses. By further coupling the replacement of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) with nonfullerene acceptors owing to better mechanical stretchability in the photoactive layer, OSCs with improved intrinsically stretchability and performance were demonstrated. An all-polymer OSC can exhibit a power conversion efficiency of 2.82% after 10% stretching, surpassing the PCBM-based device that can only withstand 5% strain.

Nonvolatile Perovskite-Based Photomemory with a Multilevel Memory Behavior.

Solution-processable organic-inorganic hybrid perovskite materials with a wealth of exotic semiconducting properties have appeared as the promising front-runners for next-generation electronic devices. Further, regarding its well photoresponsibility, various perovskite-based photosensing devices are prosperously developed in recent years. However, most exploited devices to date only transiently transduce the optical signals into electrical circuits while under illumination, which necessitates using additional converters to further store the output signals for recording the occurrence of light stimulation. Herein, a nonvolatile perovskite-based floating-gate photomemory with a multilevel memory behavior is demonstrated, for which a floating gate comprising a polymer matrix impregnated with perovskite nanoparticles is employed. Owing to the well photoresponsibility introduced by the embedded nanoparticles, the device is enabled to access multiple wavelength response and the functionalities of recording power/time-dependent illumination under no vertical electrical field. Intriguingly, a nonvolatility of photorecording exceeding three months with a high On/Off current ratio over 104 can be achieved.

Rigidifying Nonplanar Perylene Diimides by Ring Fusion Toward Geometry-Tunable Acceptors for High-Performance Fullerene-Free Solar Cells.

Rigid fused perylene diimide (PDI) dimers bridged with heterocycles exhibit superior photovoltaic performance compared to their unfused semiflexible analogues. Changing the chalcogen atoms in the aromatic bridges gradually increases the twist angles between the two PDI planes, leading to a varied morphology in which the one bridged by thiophene achieves a balance and shows the best efficiency of 6.72%.