The long‐term operational stability of perovskite light‐emitting diodes (PeLEDs), especially red PeLEDs with only several hours typically, has always faced great challenges. Stable β‐CsPbI3 nanocrystals (NCs) are demonstrated for highly efficient and stable red‐emitting PeLEDs through incorporation of poly(maleic anhydride‐alt‐1‐octadecene) (PMA) in synthesizing the NCs. The PMA can chemically interact with PbI2 in the precursors via the coupling effect between O groups in PMA and Pb2+ to favor crystallization of stable β‐CsPbI3 NCs. Meanwhile, the cross‐linked PMA significantly reduces the PbCs anti‐site defect on the surface of the β‐CsPbI3 NCs. Benefiting from the improved crystal phase quality, the photoluminescence quantum yield for β‐CsPbI3 NCs films remarkably increases from 34% to 89%. The corresponding red‐emitting PeLEDs achieves a high external quantum efficiency of 17.8% and superior operational stability with the lifetime, the time to half the initial electroluminescence intensity (T50) reaching 317 h at a constant current density of 30 mA cm−2.

There has been rapid progress in solution-processed organic solar cells (OSCs) and perovskite solar cells (PVSCs) toward low-cost and highthroughput photovoltaic technology. Carrier (electron and hole) transport layers (CTLs) play a critical role in boosting their efficiency and long-time stability. Solution-processed metal oxide nanocrystals (SMONCs) as a promising CTL candidate, featuring robust process conditions, low-cost, tunable optoelectronic properties, and intrinsic stability, offer unique advantages for realizing cost-effective, high-performance, large-area, and mechanically flexible photovoltaic devices. In this review, the recent development of SMONC-based CTLs in OSCs and PVSCs is summarized. This paper starts with the discussion of synthesis approaches of SMONCs. Then, a broad range of SMONC-based CTLs, including hole transport layers and electron transport layers, are reviewed, in which an emphasis is placed on the improvement of the efficiency and device stability. Finally, for the better understanding of the challenges and opportunities on SMONC-based CTLs, several strategies and perspectives are outlined.

This study proposes a novel strategy of controllable deamination of Co–NH3 complexes in a system containing Ni(OH)2 to synthesize ultrasmall ternary oxide nanoparticles (NPs), NiCo2O4. Through this approach, ultrasmall (5 nm on average) and well‐dispersed NiCo2O4 NPs without exotic ligands are obtained, which enables the formation of uniform and pin‐hole free films. The tightly covered NiCo2O4 films also facilitate the formation of large perovskite grains and thus reduce film defects. The results show that with the NiCo2O4 NPs as the hole transport layer (HTL), the perovskite solar cells reach a high power conversion efficiency (PCE) of 18.23% and a promising stability (maintained ≈90% PCE after 500 h light soaking). To the best of the author's knowledge, it is the first time that spinel NiCo2O4 NPs have been applied as hole transport layer in perovskite solar cells successfully. This work not only demonstrates the potential applications of ternary oxide NiCo2O4 as HTLs in hybrid perovskite solar cells but also provides an insight into the design and synthesis of ultrasmall and ligand‐free NPs HTLs to enable cost‐effective photovoltaic devices.

Emerging novel metal electrodes not only serve as the collector of free charge carriers, but also function as light trapping designs in photovoltaics. As a potential alternative to commercial indium tin oxide, transparent electrodes composed of metal nanowire, metal mesh, and ultrathin metal film are intensively investigated and developed for achieving high optical transmittance and electrical conductivity. Moreover, light trapping designs via patterning of the back thick metal electrode into different nanostructures, which can deliver a considerable efficiency improvement of photovoltaic devices, contribute by the plasmon-enhanced light-mattering interactions. Therefore, here the recent works of metal-based transparent electrodes and patterned back electrodes in photovoltaics are reviewed, which may push the future development of this exciting field.

Organic–inorganic halide hybrid perovskite materials are promising materials for X‐ray and photon detection due to their superior optoelectronic properties. Single‐crystal (SGC) perovskites have increasingly attracted attention due to their substantially low crystal defects, which contribute to improving the figures of merit of the devices. Cuboid CH3NH3PbI3 SGC with the naturally favorable geometry for device fabrication is rarely reported in X‐ray and photon detection application. The concept of seed dissolution‐regrowth to improve crystal quality of cuboid CH3NH3PbI3 SGC is proposed and a fundamental understanding of the nucleation and growth is provided thermodynamically. The X‐ray detector fabricated from cuboid CH3NH3PbI3 SGC demonstrates the firstly reported high sensitivity of 968.9 µC−1 Gy−1 cm−2 under −1 V bias. The results also show that the favorable crystal orientation and high quality of cuboid CH3NH3PbI3 leads to better responsivity and faster response speed than the more common dodecahedral CH3NH3PbI3 in photodetection. Consequently, the work paves a way to synthesize high‐quality perovskite SGCs and benefits the application of MAPbI3 SGCs with preferred crystal orientation and favorable crystal geometry for emerging device applications.