Solution‐processed nickel oxide nanocrystals (NiOx NCs) ink can be facilely applied to deposit NiOx thin films as the hole transport layer (HTL) for perovskite solar cells (PSCs). Both the efficiency and stability of the corresponding PSCs depend significantly on the size and the energy levels of the as‐synthesized NiOx NCs; however, previous studies have shown that these two aspects can be hardly controlled synchronously to maximize the device performance. Herein, a novel synthesis of highly dispersed NiOx NCs is demonstrated by employing tetraalkylammonium hydroxides (TAAOHs, alkyl = methyl, ethyl, propyl, butyl) as precipitating bases, where the varied alkyl chain lengths of TAAOHs enable the size control of the NiOx NCs and the subsequent altering of their Ni3+ contents, leading to tunable energy levels of the NiOx thin films. With the longest butyl chain, the smallest crystal size and the optimal energy level alignment at the NiOx/perovskite interface are achieved. After further passivating the detrimental Ni3+ species on the surface of NiOx HTL, a remarkable power conversion efficiency (PCE) approaching 23% is obtained, which is one of the highest PCEs reported for NiOx‐based inverted PSCs. Furthermore, the unencapsulated device exhibits excellent ultraviolet stability, which maintains ≈87% of its PCE after 200 h exposure.

An active and precise method for three-dimensional (3D) droplet manipulation is introduced. By modulating the local electrostatic force acting on droplets in carrier oil between needle plate electrodes, the vertical motion of droplets can be controlled, including the droplet levitation at the interface between the carrier oil and the air. Levitated droplets can be translated horizontally with high efficiency by the motion of the needle electrode. With controllable local deformation on the flexible plate electrode, selective manipulation can be realized for multiple droplets. Applying the manipulation method proposed, a platform is built and various droplet handling, such as transport, merging, and mixing, is performed effectively. Complex droplet transport trajectories are achieved by moving the needle electrode. The droplet transport velocity can reach up to 37 mm/s. The introduced method has fundamental advantages of avoiding cross-contamination between droplets, enhancing the flexibility, eliminating the transport track constraint, and lowering costs with straightforward and precise droplet manipulation.

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Droplet manipulation is the cornerstone of many modern technologies. It is still challenging to drive the droplet motion on nonslippery surfaces flexibly. We present a droplet manipulation method on nonslippery polymer surfaces based on the corona discharge. With the corona discharge of two-needle electrodes with opposite polarities, the droplet's charge polarity can be switched, which results in the directionally droplet transport on a charged polymer surface with the oscillation. Here, such droplet behaviors are presented in detail. Dependence of the motion on the critical distance and driving distance between the droplet and the needle electrode is revealed. The driving mechanism is verified by experiments and simulations. This work enriches the droplet manipulation techniques on nonslippery surfaces for various applications, such as combinatory chemistry, biochemical, and medical detection.

Charged droplets driven by Coulomb force are an important part of a droplet-based micro reactor. In this study, we realized the rapid oscillatory motion of droplets both in oil and on superhydrophobic surface by injecting charges through corona discharge. Distinct from the oscillatory motion of water droplets under a DC electric field, charge injection can make the motion of water droplets more flexible. A droplet in the oil layer can move up and down regularly under the action of corona discharge, and the discharge voltage can control the movement period and height of the droplet. In addition, the left–right translation of droplets on a superhydrophobic surface can be achieved by injecting charges into the hydrophobic film surface through corona discharge. Two kinds of droplet motion behaviors are systematically analyzed, and the mechanism of droplet motion is explained. The present results could help establish new approaches to designing efficient machines in microfluidics and micromechanical equipment.