All‐inorganic perovskite CsPbI3 quantum dots (QDs) offer much better stability for photovoltaic applications. Unfortunately, their cell efficiencies are hindered by the low carrier transport efficiency of QD‐assembled films. In addition, agglomeration‐induced phase change of QDs poses another problem for material and device degradation. Herein, the use of µ‐graphene (µGR) to crosslink QDs to form µGR/CsPbI3 film is demonstrated. It is found that the resultant QDs film provides not only an effective channel for carrier transport, as witnessed by much improved conductivity but also significantly better stability against moisture, humidity, and high temperature stresses. The µGR/CsPbI3 based solar cell shows increased device performance. More specifically, compared to the solar cell without the µGR treatment, VOC is improved to 1.18 from 1.16 V, JSC to 13.59 from 13.17 mA cm−2, and FF to 72.6 from 68.1%, and overall power conversion efficiency to as high as 11.40 from 10.41%, a 12% increase. In addition, the instability originating from the thermal/moisture‐induced QD agglomeration is also greatly suppressed by the µGR crosslinking. The optimized device retains >98% of its initial efficiency after being stored in N2 atmosphere for one month. Importantly, under 60% humidity and 100 °C thermal stresses, the µGR/CsPbI3 devices show much better stability.

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In order to explore a new family of phosphate phosphors, the synthesis and crystal structure of a novel phosphate family, Ca 19 M 2 (PO 4 ) 14 (M ¼ Mg, Zn, Mn), were investigated. Eu 3+ doped Ca 19 Mg 2 (PO 4 ) 14 red phosphor was also successfully synthesized with the objective of application in ultraviolet-based lightemitting diodes (LEDs) and field emission displays (FEDs). The characteristic photoluminescence properties were studied in detail by photoluminescence excitation (PLE), emission (PL) spectra and decay times. The Ca 19 Mg 2 (PO 4 ) 14 :0.06Eu 3+ phosphor offers higher brightness and thermal stability than the commercial Y 2 O 3 :Eu 3+ . The unexpected temperature-dependent luminescence from higher 5 D 1 states was observed and was explained via the configuration coordinate diagram. The cathodoluminescence (CL) spectra as a function of accelerating voltage and probe current were also measured. Excellent degradation properties with good color stability were obtained by continuous low-voltage electronbeam excitation of the phosphor. The results indicate that the phosphor Ca 19 Mg 2 (PO 4 ) 14 :0.06Eu 3+ can be a suitable red-emitting phosphor candidate for LEDs and FEDs.

A series of novel red emission Mg3Ga2GeO8 (MGG):Mn(4+) phosphors under near-UV (NUV) excitation are synthesized successfully by traditional high-temperature solid-state reaction. The structure of Mg3Ga2GeO8 is investigated by high-resolution transmission electron microscopy, scanning electron microscopy, and powder X-ray diffraction (XRD) Rietveld refinement. It has one octahedral site and one tetrahedral site in the crystal structure. According to XRD and photoluminescence (PL) property analysis, Mn(4+) can occupy an octahedral (Mg(2+)/Ga(3+)) site. The PL properties are investigated by diffuse-reflectance, emission, excitation, and temperature-dependent spectroscopy and decay curves. It can emit red light peaking at 659 nm under NUV excitation. The critical quenching concentration of Mn(4+) was about 0.5 mol %. The concentration quenching mechanism could be a d-d interaction for the Mn(4+) center. The CIE chromaticity coordinates and full-width at half-maximum are (0.295, 0.677) and 24 nm, respectively. It demonstrated that MGG:Mn(4+) has high color purity. The PL intensity of MGG:0.5% Mn(4+) drops to 72% when the temperature is raised up to 150 °C. Furthermore, MGG:0.5% Mn(4+) exhibits outstanding quantum efficiency (64.7%). By tuning of the weight ratio of blue, green, and red phosphors, the fabricated white-light-emitting diodes using a 405 nm GaN NUV chip combined with a blend of blue phosphor BAM:Eu(2+), green phosphor Sr2SiO4:Eu(2+), and red-emitting phosphor MGG:Mn(4+) driven by 40 mA current can get white light with chromaticity coordinates (0.316, 0.375) and CCT = 3340 K. This demonstrates that MGG:Mn(4+) is a potential red phosphor matching NUV LED chips to get white light.

Defects are considered to be one of the most significant factors that compromise the power conversion efficiencies and long‐term stability of perovskite solar cells. Therefore, it is urgent to have a profound understanding of their formation and influence mechanism, so as to take corresponding measures to suppress or even completely eliminate their adverse effects on device performance. Herein, the possible origins of the defects in metal halide perovskite films and their impacts on the device performance are analyzed, and then various methods to reduce defect density are introduced in detail. Starting from the internal and interfacial aspects of the metal halide perovskite films, several ways to improve device performance and long‐term stability including additive engineering, surface passivation, and other physical treatments (annealing engineering), etc., are further elaborated. Finally, the further understanding of defects and the development trend of passivation strategies are prospected.