51ÁÔÆæÈë¿Ú

Abstract:

Lead-based halide perovskites have received great attention in light-emitting applications due to their excellent properties, including high photoluminescence quantum yield (PLQY), tunable emission wavelength, and facile solution preparation. In spite of excellent characteristics, the presence of toxic element lead directly obstructs their further commercial development. Hence, exploiting lead-free halide perovskite materials with superior properties is urgent and necessary. In this review, the deep-seated reasons that benefit light emission for halide perovskites, which help to develop lead-free halide perovskites with excellent performance, are first emphasized. Recent advances in lead-free halide perovskite materials (single crystals, thin films, and nanocrystals with different dimensionalities) from synthesis, crystal structures, optical and optoelectronic properties to applications are then systematically summarized. In particular, phosphor-converted LEDs and electroluminescent LEDs using lead-free halide perovskites are fully examined. Ultimately, based on current development of lead-free halide perovskites, the future directions of lead-free halide perovskites in terms of materials and light-emitting devices are discussed.

Abstract:

Poly(N-(5-(5-norbornene-2-carbonyl)oxy)pentyl)-N′-n-hexyl-naphthalene-1,8:4,5-bis(dicarboximide) has been synthesized by esterification of (N-(5-hydroxypentyl)-N′-n-hexyl-naphthalene-1,8:4,5-bis(dicarboximide)) with exo-5-norbornene-2-carboxylic acid, and has been polymerized using the first-generation Grubbs initiator. This side-chain polymer exhibits good transparency throughout the visible (absorption onset at ca. 400 nm), good solubility in common low- and medium-polarity organic solvents, good resistance to dimethylformamide, and appropriate electron affinity for use as an electron-extraction layer in lead-halide perovskite solar cells. The performance of this polymer in n-i-p perovskite solar cells was compared to that of several small-molecule naphthalene-1,8:4,5-bis(dicarboximide) derivatives and of SnO2. Solar cells using the polymer exhibited open-circuit voltages of up to 1.02 V, short-circuit currents of over 21 mA cm-2, and power conversion efficiencies (PCE) reaching 14% which stabilize at 13.8% upon 90 s of illumination. Meanwhile control SnO2 devices exhibited a PCE of ca. 16%, and small-molecule devices gave PCE values of less than 10%. The devices employing the polymer exhibited improved long-term stability relative to the SnO2 control devices under continuous illumination.

Abstract:

Light-emitting devices (LEDs) with inorganic perovskite nanocrystals (PNCs) fabricated through the all-solution process have tremendous potential for new-generation illumination and displays on account of their large area and cost-effective manufacturing. However, the development of efficient solution-processed PNC LEDs remains challenge, which mainly results from the fact that only a few types of charge transport layers can be employed for the subsequent deposition steps, thus leading to injection barriers and charge injection imbalance inside these LEDs. Herein 4,4'-bis(carbazole-9-yl) biphenyl (CBP) is introduced as a dopant into the poly(9,9-dioctylfluorene-co-N-(4-(3-methylpropyl)) diphenylamine) (TFB) hole transport layer (HTL), which efficiently modulates the mobility of charge carrier as well as the energy level of the HTL, resulting in the barrier-free injection of the charge carrier in the as-fabricated solution-processed PNC LEDs. Consequently, the luminance of red LEDs (688 nm) reaches 2990 cd m^-2, and the external quantum efficiency achieves 8.1%, which is the optimal performance for solution-processed PNC LEDs to date. Additionally, the turn-on voltage and roll-off have also been improved by the more balanced charge injection.