Formamidinium (FA)-based perovskites remained state-of-the-art in the field of perovskite solar cells (PSCs) owing to the exceptional absorption and carrier transport properties, while the transition from photoactive (α-) to photoinactive (δ-FAPbI 3 ) phase is the impediment that causes performance degradation and thus limits the deployment of FA-based PSCs. The unfavorable phase transition originates from tensile strain in the FAPbI 3 crystal lattice, which undergoes structural reorganization for lattice strain balancing. In this work, we found that the ionic liquid (IL) could be used as the strain coordinator to balance the lattice strain for stability improvement of FAPbI 3 perovskite. We theoretically studied the electronic coupling between IL and FAPbI 3 and unraveled the originality of the IL-induced compressive strain. The strain-relaxed α-FAPbI 3 by IL showed robust stability against environmental factors, which can withstand ambient aging for 40 days without any phase transition or decomposition. Moreover, the strain-relaxed perovskite films showed a lower trap density and resulted in conversion efficiency improvement from 18.27 to 19.88%. Based on this novel strain engineering strategy, the unencapsulated PSCs maintained 90% of their initial efficiency under ambient-air aging for 50 days.
Perovskites have become a promising light-absorbing material for the fabrication of high-performance solar cells. But, the relatively low film quality of perovskites hinders the fabrication of large-area perovskite solar modules and long-period stability, which further slows down their industrial-scale commercialization. Here, we propose an N,N′-methylenebis(acrylamide) (MBAA) addition strategy for modulating grain crystallization and ion migration within methylammonium lead halide (MAPbI 3 ), resulting in enhanced power conversion efficiency (PCE) and stability of MAPbI 3 -based solar modules. MBAA can help to form larger perovskite grains with less defects due to strong coordination interactions between the Pb atoms in MAPbI 3 and the −NH and −CO functional groups in MBAA. We further found that MBAA was located at the surface of perovskite grains, which would block the ion migration (MA + /I − ) and the H 2 O/O 2 infusion from the ambient-air environment, resulting in enhancements of the PCE and stability of the MAPbI 3 devices. The mini-module with an active area of 20 cm 2 exhibits a record PCE of 18.58%. The MBAA-based solar module shows excellent damp heat and operational stabilities and maintains ∼82% and ∼90% of its initial PCE after 1000 h under 85 °C/85% relative humidity and 1000 h working at the maximum power point.
The demand for wearable sensors is vastly growing as it provides people the ability to monitor their daily activities, surrounding environment, and health conditions conveniently. The development of these sophisticated wearable sensors with specific- or multiple-function capacity largely depends on the innovation pace of fabrication technologies. This review focuses on the most recent development of micro/nanofiber fabrication technologies for fabricating wearable sensors, including drawing, spinning, coating, and printing. The basic working mechanisms are introduced, followed by some representative applications. Lastly, the perspectives of these advanced methods on the development of future wearable sensors are discussed.
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