One-Stone-for-Two-Birds Method to Improve the SnO2 Layers for High Power-per-Weight Flexible Perovskite Solar Cell Mini-modules.

Maintaining the power conversion efficiency (PCE) of flexible perovskite solar cells (fPSCs) while decreasing their weight is essential to utilize their lightweight and flexibility as much as possible for commercialization. Strengthening the interfaces between functional layers, such as flexible substrates, charge transport layers, and perovskite active layers, is critical to addressing the issue. Herein, we propose a feasible and one-stone-for-two-birds method to improve the electron transport layer (ETL), SnO2, and the interface between the ETL and perovskite layer simultaneously. In detail, poly(acrylate ammonium) (PAAm), a low-cost polymer with a long chain structure, is added into the SnO2 aqueous solution to reduce the aggregation of SnO2 nanoparticles, resulting in the deposition of a conformal and high-quality ETL film on the tin-doped indium oxide film surface. Simultaneously, PAAm addition can effectively regulate the crystallization of the perovskite films, strengthening the interface between the SnO2 film and the buried surface of the perovskite layer. The outstanding PCEs of 22.41% on small-scale fPSCs and 18.54% on fPSC mini-modules are among the state-of-the-art n-i-p type fPSCs. Moreover, the fPSC mini-module on the 20 µm-thick flexible substrate shows a comparable PCE with that of the fPSC mini-module on the 125 µm-thick flexible substrate, exhibiting a high power-to-weight of 5.097 W/g. This work provides an easy but essential direction for further applications of fPSCs in diverse scenarios.

How to Stabilize the Current of Efficient Inverted Flexible Perovskite Solar Cells at the Maximum Power Point.

Inverted flexible perovskite cells (fPSCs) have attracted much attention for their high efficiency and power per weight. Still, the steady-state output is one of the critical factors for their commercialization. In this paper, it is found that the steady-state current of inverted fPSCs based on nickel oxide nanoparticles (n-NiOx) continuously decreases under light illumination. Conversely, those based on magnetron-sputtered NiOx (sp-NiOx) exhibit the opposite result. Based on visualization of ion migration in the photoluminescence (PL) imaging microscopy tests, the discrepancies in the buried surfaces lead to the differences in ion migration in perovskite films, which triggers the temporary instability of the output current of devices during operation. The DFT theoretical calculation and experimental results reveal that NiOx films with different contents of Ni vacancies can modulate the crystallization of the perovskite films on the NiOx surfaces. Tuning the crystallization of the perovskite films is essential to stabilize the output current of fPSCs at a steady state. To demonstrate that, capsaicin is doped into the perovskite solutions to improve the quality of the perovskite buried interface. Finally, the corresponding fPSCs exhibit outstanding efficiency and stability during operation. These results provide valuable scientific guidance for fabricating fPSCs with stable operation under illumination conditions.

Phase-Engineering of Layered Nickel Hydroxide for Synthesizing High-Quality NiOx Nanocrystals for Efficient Inverted Flexible Perovskite Solar Cells.

Nickel oxide (NiOx) nanocrystals have been widely used in inverted (p-i-n) flexible perovskite solar cells (fPSCs) due to their remarkable advantages of low cost and outstanding stability. However, anion and cation impurities such as NO3- widely exist in the NiOx nanocrystals obtained from calcinated nickel hydroxide (Ni(OH)2). The impurities impair the photovoltaic performance of fPSCs. In this work, we report a facile but effective way to reduce the impurities within the NiOx nanocrystals by regulating the Ni(OH)2 crystal phase. We add different alkalis, such as organic ammonium hydroxide and alkali metal hydroxides, to nickel nitrate solutions to precipitate layered Ni(OH)2 with different crystalline phase compositions (α and ß mixtures). Especially, Ni(OH)2 with a high ß-phase content (such as from KOH) has a narrower crystal plane spacing, resulting in fewer residual impurity ions. Thus, the NiOx nanocrystals, by calcinating the Ni(OH)x with excess ß phase from KOH, show improved performance in inverted fPSCs. A champion power conversion efficiency (PCE) of 20.42% has been achieved, which is among the state-of-art inverted fPSCs based on the NiOx hole transport material. Moreover, the reduced impurities are beneficial for enhancing the fPSCs' stability. This work provides an essential but facile strategy for developing high-performance inverted fPSCs.

Engineered tunneling layer with enhanced impact ionization for detection improvement in graphene/silicon heterojunction photodetectors.

Here, an engineered tunneling layer enhanced photocurrent multiplication through the impact ionization effect was proposed and experimentally demonstrated on the graphene/silicon heterojunction photodetectors. With considering the suitable band structure of the insulation material and their special defect states, an atomic layer deposition (ALD) prepared wide-bandgap insulating (WBI) layer of AlN was introduced into the interface of graphene/silicon heterojunction. The promoted tunneling process from this designed structure demonstrated that can effectively help the impact ionization with photogain not only for the regular minority carriers from silicon, but also for the novel hot carries from graphene. As a result, significantly enhanced photocurrent as well as simultaneously decreased dark current about one order were accomplished in this graphene/insulation/silicon (GIS) heterojunction devices with the optimized AlN thickness of ~15 nm compared to the conventional graphene/silicon (GS) devices. Specifically, at the reverse bias of -10 V, a 3.96-A W-1 responsivity with the photogain of ~5.8 for the peak response under 850-nm light illumination, and a 1.03-A W-1 responsivity with ∼3.5 photogain under the 365 nm ultraviolet (UV) illumination were realized, which are even remarkably higher than those in GIS devices with either Al2O3 or the commonly employed SiO2 insulation layers. This work demonstrates a universal strategy to fabricate broadband, low-cost and high-performance photo-detecting devices towards the graphene-silicon optoelectronic integration.

A "time-frozen" technique in microchannel used for the thermodynamic studies of DNA origami.

The emergence of DNA origami greatly accelerated the development of DNA nanotechnology. A thorough understanding of origami thermodynamics is very important for both fundamental studies and practical applications. These thermodynamic transitions usually take place in several seconds or even less, and are very difficult to monitor by conventional methods. Numerous tests are required to characterize the origami molecule's behaviors at different temperatures, which is very labor-intensive and time-consuming. In this paper, an axially distributed temperature gradient along a capillary was formed in a spatially varying temperature field. In such a temperature gradient, the origami molecule's thermodynamic processes occur and remain stable at every position along the capillary's microchannel. It looks like the time of the thermodynamic process is frozen along the microchannel. With this method, the origami molecule's thermodynamic characteristics at different temperatures can be obtained in a single experiment, and rapid processes can be monitored with ease by conventional methods for an adequate time period at low cost. In order to show its potential abilities, this method has been demonstrated in applications which the origami's assembly, denaturation and strand displacement are carry out in a flowing or stationary solution.

Millifluidic chip with a modular design used as a sample pretreatment cartridge for flour and flour food products.

The integration of sample pretreatment remains one of the hurdles towards a rapid, automated micro total analytical system (µ-TAS) for real samples. In this paper, a modular design, which was used for sample preparation, has been developed as the polydimethylsiloxane (PDMS) millifluidic chips with channels at a millimeter level. Multiple functional units, including extraction, filtration, mixing and solid phase extraction (SPE), for sample pretreatment were integrated in one chip. In this chip, each functional unit was connected by pump tubings and one-way valves in series to form a fully automated system. Based on the modular design, multiple functional units have been combined in different sequences according to practical needs. In addition, the proposed system has characteristics of miniaturization, portability, and real-time application. Herein, spiked benzoyl peroxide (BPO) in flour samples was used as a model compound to study the system's performances. With a portable integrated Raman spectrometer for detection, the detection limit of BPO was 0.017gkg-1, with a linear relationship from 0.025 to 0.5gkg-1. This modular design was demonstrated to be effective and it can be expanded for pretreatment of other food samples.