RESUMEN
Carbon dots (CDs) as one of the most promising carbon-based nanomaterials are inspiring extensive research in optoelectronic applications. White-light-emitting diodes (WLEDs) with tunable correlated color temperatures (CCTs) are crucial for applications in white lighting. However, the development of high-performance CDs-based electroluminescent WLEDs, especially those with adjustable CCTs, remains a challenge. Herein, white CDs-LEDs with CCTs from 2863 to 11 240 K are successfully demonstrated by utilizing aggregation-induced emission red-shifting and broadening of CDs. As a result, a series of warm white, pure white, and cold white CDs-LEDs are realized with adjustable emissions in sequence along the blackbody radiation curve. These CDs-LEDs reach maximum brightness and external quantum efficiency up to 1414-4917 cd m-2 and 0.08-0.87%, respectively, which is among the best performances of white CDs-LEDs. To the best of the authors' knowledge, this is the first time that CCT-tunable white electroluminescent CDs-LEDs are demonstrated through controlling the aggregation degrees of CDs.
RESUMEN
Hole-transporting materials (HTMs) play a major role in efficient and stable perovskite solar cells (PSCs), especially for CsPbI2Br inorganic PSC. Among them, dopant-free conjugated polymers attract more attention because of the advantages of high hole mobility and high stability. However, the relationship between the polymer structure and the photovoltaic performance is rarely investigated. In this work, we choose three similar D-π-A-type polymers, where the D unit and π-bridge are fixed into benzodithiophene and thiophene, respectively. By changing the A units from classic benzodithiophene-4,8-dione and benzotriazole to quinoxaline, three polymers PBDB-T, J52, and PE61 are utilized as dopant-free HTMs for CsPbI2Br PSCs. The energy levels, hole mobility, and molecular stacking of the three HTMs, as well as charge transfer between CsPbI2Br/HTMs, are fully investigated. Finally, the device based on PE61 HTM obtains the champion power conversion efficiency of 16.72%, obviously higher than PBDB-T (15.13%) and J52 (15.52%). In addition, the device based on PE61 HTM displays the best long-term stability. Those results demonstrate that quinoxaline is also an effective A unit to construct D-π-A-type polymers as HTMs and improve the photovoltaic performance of PSCs.
RESUMEN
Deep-red light-emitting diodes (DR-LEDs, >660 nm) with high color-purity and narrow-bandwidth emission are promising for full-color displays and solid-state lighting applications. Currently, the DR-LEDs are mainly based on conventional emitters such as organic materials and heavy-metal based quantum dots (QDs) and perovskites. However, the organic materials always suffer from the complicated synthesis, inferior color purity with full-width at half-maximum (FWHM) more than 40 nm, and the QDs and perovskites still suffer from serious problems related to toxicity. Herein, this work reports the synthesis of efficient and high color-purity deep-red carbon dots (CDs) with a record narrow FWHM of 21 nm and a high quantum yield of more than 50% from readily available green plants. Moreover, an exciplex host is further established using a polymer and small molecular blend, which has been shown to be an efficient strategy for producing high color-purity monochrome emission from deep-red CDs via Förster energy transfer (FET). The deep-red CD-LEDs display high color-purity with Commission Internationale de l'Eclairage (CIE) coordinates of (0.692, 0.307). To the best of the knowledge, this is the first report of high color-purity CD-LEDs in the deep-red region, opening the door for the application of CDs in the development of high-resolution light-emitting display technologies.
RESUMEN
Impurity doping is an effective approach to tuning the optoelectronic performance of host materials by imparting extrinsic electronic channels. Herein, a family of lanthanide (Ln3+) ions was successfully incorporated into a Bi:Cs2AgInCl6 lead-free double-perovskite (DP) semiconductor, expanding the spectral range from visible (Vis) to near-infrared (NIR) and improving the photoluminescence quantum yield (PLQY). After multidoping with Nd, Yb, Er and Tm, Bi/Ln:Cs2AgInCl6 yielded an ultrabroadband continuous emission spectrum with a full width at half-maximum of ~365 nm originating from intrinsic self-trapped exciton recombination and abundant 4f-4f transitions of the Ln3+ dopants. Steady-state and transient-state spectra were used to ascertain the energy transfer and emissive processes. To avoid adverse energy interactions between the various Ln3+ ions in a single DP host, a heterogeneous architecture was designed to spatially confine different Ln3+ dopants via a "DP-in-glass composite" (DiG) structure. This bottom-up strategy endowed the prepared Ln3+-doped DIG with a high PLQY of 40% (nearly three times as high as that of the multidoped DP) and superior long-term stability. Finally, a compact Vis-NIR ultrabroadband (400~2000 nm) light source was easily fabricated by coupling the DiG with a commercial UV LED chip, and this light source has promising applications in nondestructive spectroscopic analyses and multifunctional lighting.