Periodic Reporting for period 1 - CuMOF-LED (White Hybrid Light-Emitting Diodes based on Cu(I) Complexes-MOFs Hybrid Materials)
Periodo di rendicontazione: 2020-09-01 al 2022-08-31
White Light-Emitting Diodes (WLEDs) currently consist of polluting, expensive and toxic rare earth-based materials (Inorganic Phosphors, IPs). These materials cannot hold the current world-wide WLED production for more than 15 years. IPs must be hence replaced by non-toxic, cos-effective and sustainable Organic Phosphors (OPs) towards a new generation of hybrid WLEDs. These are nevertheless still too costly/polluting/toxic for a widespread commercialization. They are indeed made by materials such as iridium (150€/g), cadmium, yttrium (4,000€/kg). Moreover, those OP-WLEDs have not met customer requirements, i.e. i) stability, ii) efficiency, iii) quality of the white. Regarding iridium, it has recently achieved interesting performances, but it is considered as a critical raw material by the European Commission. Obvious candidates to replace iridium complexes are copper complexes. Advantages of copper complexes are straightforward synthesis, low cost (7000€/T), and efficiency. However, Cu(I) complexes feature a remarkable lack of stability. In addition, intrinsic white-emitting Cu(I) complexes have not been reported yet.
Typically, numerous WHLEDs feature excellent color rendering index (CRI >80), color correlated temperature (CCT > 5500K for a cold white, and < 5500K for a warm white), and x/y Commission Internationale de l’Eclairage (CIE) coordinates around 0.33/0.33. Yet, their stability strongly depends on the phosphor. Another important parameter is the photoluminescence quantum yield (PLQY).
In the context of solution statement and strategy, CuMOF-LED proposes to develop a new family of white hybrid OPs based on the combination of bluish green emissive copper complexes embedded into yellowish orange emissive and sustainable metal organic framework (MOFs). MOFs are a class of porous crystalline materials and are here useful for two reasons: i) their porosity is used for copper-based materials encapsulation, providing more stabilization, ii) and they provide a color contribution, necessary for achieving the white emission. This final system is called host-guest hybrid material and leads to white hybrid LED (WHLED), in which hosts are the MOFs and guests are the copper complex This concept is important for our society since it would reduce drastically the ecological impact of LED fabrication, as stated by EU action line.
The MOFs are based on an organic moiety, called ligand, and a metallic node. The latter is, for sustainable and cost purposes, zinc, zirconium, aluminum, or magnesium. The syntheses, purifications, characterizations and photophysical properties of hosts (MOFs) and guests (Cu(I)) complexes and organic emitters were timely achieved. However, the implementation of host-guest systems based on Cu(I) was not successful, despite numerous trials. This was related to i) the guest is too big to enter the hosts’ pore size; and/or ii) the guests are too instable and get oxidized/degraded before entering the hosts’ pore size. Therefore, Cu(I) complexes were replaced by organic dyes, since they are smaller and more stable in solution. In this regard, white emissive hybrid materials, and consequently WHLEDs, were successfully achieved. In a sociological point view, this project goes beyond the state-of-the-art in a sustainable approach.
In the context of solution statement and strategy, CuMOF-LED proposes to develop a new family of white hybrid OPs based on the combination of bluish green emissive copper complexes embedded into yellowish orange emissive and sustainable metal organic framework (MOFs). MOFs are a class of porous crystalline materials and are here useful for two reasons: i) their porosity is used for copper-based materials encapsulation, providing more stabilization, ii) and they provide a color contribution, necessary for achieving the white emission. This final system is called host-guest hybrid material and leads to white hybrid LED (WHLED), in which hosts are the MOFs and guests are the copper complex This concept is important for our society since it would reduce drastically the ecological impact of LED fabrication, as stated by EU action line.
The MOFs are based on an organic moiety, called ligand, and a metallic node. The latter is, for sustainable and cost purposes, zinc, zirconium, aluminum, or magnesium. The syntheses, purifications, characterizations and photophysical properties of hosts (MOFs) and guests (Cu(I)) complexes and organic emitters were timely achieved. However, the implementation of host-guest systems based on Cu(I) was not successful, despite numerous trials. This was related to i) the guest is too big to enter the hosts’ pore size; and/or ii) the guests are too instable and get oxidized/degraded before entering the hosts’ pore size. Therefore, Cu(I) complexes were replaced by organic dyes, since they are smaller and more stable in solution. In this regard, white emissive hybrid materials, and consequently WHLEDs, were successfully achieved. In a sociological point view, this project goes beyond the state-of-the-art in a sustainable approach.
In this context, sustainable and cost-effective blue-emitting Zn-based MOF and its host:guest hybrid material with red-emitting rhodamine B (RhB) emitter RhB@LMOF were used to make blue- and white- emitting HLEDs. LMOF features a high blue emission in polystyrene coatings (PLQY=70%). Likewise, hybrid RhB@LMOF features a high white emission with PLQY of 30-40 % in polystyrene coatings. They lead to blue (LMOF; x/y CIE color coordinates of 0.28/0.47) and white (RhB@LMOF; x/y CIE color coordinates of 0.31/0.32) colors. HLEDs with stabilities of 20 h and 45 h at 50 mA on-chip under ambient operation, respectively, were performed. Though this device performance is average in HLEDs, the device degradation was mainly attributed to the photo-induced oxidation of the ligand in the MOF structure that further leads to the RhB degradation, a key information for future developments in luminescent MOFs.