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New circular polarized light-emitting electrochemical cells.

Periodic Reporting for period 1 - NEWCPLECS (New circular polarized light-emitting electrochemical cells.)

Reporting period: 2018-08-01 to 2020-07-31

Thin-film organic-based lighting devices has been one of the most relevant technological fields since the last 25 years. Light-emitting electrochemical cells (LECs) and organic light emitting diodes (OLEDs) are leading examples of this technology. While OLEDs show disadvantages, such as a complex architecture and need of a rigorous encapsulation, LECs are single-layer devices using air-stable electrodes.

The complex fabrication of multi-layered architectures on non-conventional substrates and the lack of recycling protocols are important roadblocks for the final cost reduction in terms of commercialization. Thus, OLEDs are prohibitively expensive for many large-scale applications, while LECs are much more competitive from an economic/manufacturing point of view.

The key feature making LECs more fit for a low-cost continuous fabrication in ambient conditions with respect to OLEDs is the presence of mobile ions in the active layer. The latter redistribute upon applying bias forming the electrochemical doping zones. In addition, the devices are fully compatible with metal-free electrodes, such as graphene or carbon nanotubes.

Nevertheless, the state of the art for competitive LECs, have been achieved only in the yellow/orange region by using luminescent polymers like Super Yellow and ionic transition metal complexes (iTMC) like Ir(III) cyclometallated complexes. In particular, the group of Prof. Ruben Costa is a pioneer on the development of Cu(I) coordination/organometallic compounds as emitter for thin-film LECs, but they found a series of limitations that require to be overcome for their application in benchmark devices.

Thus, one objective stablished for this project was to overcome the low stability of Cu-iTMC based LECs.
In this context, NEWCPLECS achieved both deep‐red and white light‐emitting electrochemical cells (LECs) using a new family of ionic red emitting copper(I) complexes. In short, the first deep‐red Cu(I)‐based LECs featuring high irradiances (≈100 µW cm−2) and excellent color stability (x/y CIE color coordinates of 0.66/0.32) over days were achieved. Besides, the first white‐emitting LEC manufactured with red‐emitting copper(I) complexes mixed with the HTM CBP in a host‐guest approach. This is the first proof‐of‐concept white‐emitting LECs (85:15% wt. of CBP:Cu-iTMC) featuring x/y CIE color coordinates of 0.31/0.32 and a high CRI of 92.

An important research line in the group is the design on new generation white light-emitting diods (WOLEDs). White light‐emitting diodes (WLEDs) combine a blue‐emitting GaN chip covered by rare earth color down‐converting filters based on yellow‐emitting phosphors like Y3Al5O12:Ce3+. The most critical drawback in actual technology is the white color quality related to high correlated color temperature (CCT) and low color rendering index (CRI) values due to insufficient low‐energy light contribution. This is of utmost relevance toward designing efficient artificial illumination for a wide range of applications. For instance, the long exposition to the strong blue component of WLEDs is known to damage the eye photoreceptors of children and elderly people. In addition, the lack of the orange/red component also affects the brain chemistry of adults with respect to, for example, the circadian rhythm.

In the design of new generation white light-emitting diods (WOLEDs) a leading alternative is biohybrid light-emitting diodes (Bio-HLEDs), aiming at replacing IPs by biophosphors without losing device efficiency, brightness, and stability. In this context, NEWCPLECS studied the potential of hybrid composites in which CTPR proteins stabilize emissive gold nanoparticles (AuNCs). This strategy, allowed a precise control of the size and place of AuNCs and increase its stability towards photodegradation, also producing higher quantum yields and reaching dual emission toward white color. Besides, the protein encodes anisotropic emission of the AuNCs. One of the objectives of this action was to find inherent polarized devices. In this context, this result could open the doors to new devices with bio-molecules inducing polarization in the hybrid devices.
The main scientific results obtained can be measured in the publication of 7 papers:
- Cunning defects: emission control by structural point defects on Cu(i)I double chain coordination polymers. Javier Conesa-Egea, Javier González-Platas, Ulises R. Rodríguez-Mendoza, José Ignacio Martínez, Ocon Pilar, Vanesa Fernández-Moreira, Rubén D. Costa, Julio Fernández-Cestau, Félix Zamora, Pilar Amo-Ochoa. J. Mater. Chem. C, 2020, 8, 1448-1458.
- Recent Advances in Solid‐State Lighting Devices Using Transition Metal Complexes Exhibiting Thermally Activated Delayed Fluorescent Emission Mechanism. Gilbert Umuhire Mahoro, Julio Fernandez‐Cestau, Jean‐Luc Renaud, Pedro B. Coto, Rubén D. Costa, Sylvain Gaillard. Adv. Optical Mater. 2020, 8, 2000260.
- Transparent and flexible high-power supercapacitors based on carbon nanotube fibre aerogels. Evgeny Senokos, Moumita Rana, Maria Vila, Julio Fernandez-Cestau, Rubén D. Costa, Rebeca Marcilla, Juan Jose Vilatela. Nanoscale, 2020, 12, 16980-16986.
- White-emitting Protein-Metal Nanocluster Phosphors for Highly Performing Biohybrid Light-Emitting Diodes. Antonio Aires, Verónica Fernández-Luna, Julio Fernández-Cestau, Rubén D. Costa, and Aitziber L. Cortajarena. Nano Lett. 2020, 20, 4, 2710–2716.
- White Light‐Emitting Electrochemical Cells Based on Deep‐Red Cu(I) Complexes. Elisa Fresta, Michael D. Weber, Julio Fernandez‐Cestau, Rubén D. Costa. Adv. Optical Mater. 2019, 7, 1900830.
- Versatile Homoleptic Naphthyl‐Acetylide Heteronuclear [Pt 2 M 4 (CC‐Np) 8 ] (M = Ag, Cu) Phosphors for Highly Efficient White and NIR Hybrid Light‐Emitting Diodes. Elisa Fresta, Julio Fernández‐Cestau, Belén Gil, Patricia Montaño, Jesús R. Berenguer, María Teresa Moreno, Pedro B. Coto, Elena Lalinde, Rubén D. Costa. Adv. Optical Mater. 2020, 8, 1901126.
- Polypyridyl ligands as a versatile platform for solid-state light-emitting devices. Babak Pashaei, Soheila Karimi, Hashem Shahroosvand, Parisa Abbasi, Melanie Pilkington, Antonino Bartolotta, Elisa Fresta, Julio Fernandez-Cestau, Rubén D. Costa, Francesco Bonaccorso. Chem. Soc. Rev., 2019, 48, 5033-5139.

Besides, the researcher was invited to the III International Workshop on Chemistry of Group 11 Elements that took place in Caparica (Portugal) in January 30 to 31, 2020.
In these collaborations, some conclusions useful for the future development of the project were obtained.
During the project, a new benchmark for Cu based LECs has been established.

Besides, the project explored the potential of new hybrid bioLECs that could provide with better illumination systems in terms of sustainable technologies and reduced energy consumption.