Hybrid organic-inorganic Light Emitting Diodes

Hybrid organic inorganic light emitting diodes are nowadays attracting great attention due to their intrinsic air stability and solution processability, which could result in low-cost, large area, light emitting devices. Despite the fact that high luminance values have been already demonstrated in recent publications, the efficiency of HyLEDs has been limited by its peculiar hole-dominated electronic mechanism. In particular, the electron injection is promoted by the hole accumulation at the metal oxide EIL/organic interface, but at the same time this mechanism leads to limits the device efficiency. It is known from the research in OLEDs that when the recombination zone is close to an interface, exciton quenching and direct charge recombination can take place. In this thesis, the design rules for standard OLEDs technology have been applied to HyLEDs in order to overcome those limitations, and new successful strategies to improve the performances of this new class of devices have been presented. Firstly, the use of a charged polymer as electron injection layer from the metal oxide to the polymer was presented. This approach leads to more efficient HyLEDs and gives the possibility of using different light-emitting polymer, allowing the tuning of the emission colour of the device through the whole range of the visible spectra. This device structure is of particular interest because a multilayer structure composed by a metal oxide cathode, a conjugated polyelectrolyte EIL, and the active polymer, was prepared completely by solution processing, thanks to the orthogonality of the solvents used to deposit the subsequent materials. In chapter 3 it is demonstrated how the hole leakage through the metal oxides EIL is an important loss factor leading to a lower exciton density in the polymer layer.The use of insulating metal oxides with very deep valence band resulted in the lowering of the current density flowing through the device. This effect is due to the high barrier for holes at the organic/metal oxide interface when using insulating materials like HfO2 or MgO. Thus, through the employment of these metal oxides, the efficiency of the HyLEDs can be successfully raised. It is well known that high efficiency in OLEDs can be raised considerably only when making use of phosphorescent species. In chapter 4, the use of triplet emitters in high efficiency solution processed HyLEDs was presented. In that particular device layout, a novel doped metal oxide cathode was used in order to enhance the electron injection into the active organic layer and prevent exciton quenching. Very high efficacy values up to 15 cd/A have been obtained by tuning the composition of the active organic materials in the polymer layers. In chapter 5,the performances displayed by HyLEDs using ZnO nanocristals exceed those obtained by employing polycrystalline ZnO thin films and the effect is attributed to the larger bandgap of the ZnO NCs caused by quantum confinement. It was shown that the bandgap diminishes upon temperature assisted agglomeration which is why best device performances were obtained when simply drying the NCs at room temperature.The use of solution-processed ZnO NCs in the absence of any thermal treatment allowed for the preparation of the first bright flexible HyLEDs. This work clearly underlines the potential of this novel class of devices and it indicates HyLEDs as a real possible competitor to the current OLED technology

Nucleant layer effect on nanocolumnar ZnO films grown by electrodeposition

Different ZnO nanostructured films were electrochemically grown, using an aqueous solution based on ZnCl2, on three types of transparent conductive oxides grow on commercial ITO (In2O3:Sn)-covered glass substrates: (1) ZnO prepared by spin coating, (2) ZnO prepared by direct current magnetron sputtering, and (3) commercial ITO-covered glass substrates. Although thin, these primary oxide layers play an important role on the properties of the nanostructured films grown on top of them. Additionally, these primary oxide layers prevent direct hole combination when used in optoelectronic devices. Structural and optical characterizations were carried out by scanning electron microscopy, atomic force microscopy, and optical transmission spectroscopy. We show that the properties of the ZnO nanostructured films depend strongly on the type of primary oxide-covered substrate used. Previous studies on different electrodeposition methods for nucleation and growth are considered in the final discussion.Facultad de Ciencias Exacta

Nucleant layer effect on nanocolumnar ZnO films grown by electrodeposition

Different ZnO nanostructured films were electrochemically grown, using an aqueous solution based on ZnCl2, on three types of transparent conductive oxides grow on commercial ITO (In2O3:Sn)-covered glass substrates: (1) ZnO prepared by spin coating, (2) ZnO prepared by direct current magnetron sputtering, and (3) commercial ITO-covered glass substrates. Although thin, these primary oxide layers play an important role on the properties of the nanostructured films grown on top of them. Additionally, these primary oxide layers prevent direct hole combination when used in optoelectronic devices. Structural and optical characterizations were carried out by scanning electron microscopy, atomic force microscopy, and optical transmission spectroscopy. We show that the properties of the ZnO nanostructured films depend strongly on the type of primary oxide-covered substrate used. Previous studies on different electrodeposition methods for nucleation and growth are considered in the final discussion.Facultad de Ciencias Exacta

Low cost hybrid solar cell integration on wall tiles

On this paper the first Building Integrated Hybrid Photovoltaic (BIHPV) cell obtained on a commercial tile is presented. The experimental techniques used allow a future low cost development of these cells for its massive use on facades for buildings. The basic concept includes a metal projected layer as back contact with an electron injection layer of electrodeposited ZnO, an organic PBCBM/P3HT photovoltaic cell with a closing TCO thin film on top. Integration with the substrate problems have been solved and allow further work on cell performance and durability.Reyes Tolosa, MD.; Orozco Messana, J.; Hernández Fenollosa, MDLÁ.; Camaratta, R.; Niedersberg Correia, Á.; Bolink, HJ.; Soriano, A.... (2011). Low cost hybrid solar cell integration on wall tiles. ECS Transactions. 41(4):141-146. doi:10.1149/1.3628619S14114641

Nucleant layer effect on nanocolumnar ZnO films grown by electrodeposition

Different ZnO nanostructured films were electrochemically grown, using an aqueous solution based on ZnCl2, on three types of transparent conductive oxides grow on commercial ITO (In2O3:Sn)-covered glass substrates: (1) ZnO prepared by spin coating, (2) ZnO prepared by direct current magnetron sputtering, and (3) commercial ITO-covered glass substrates. Although thin, these primary oxide layers play an important role on the properties of the nanostructured films grown on top of them. Additionally, these primary oxide layers prevent direct hole combination when used in optoelectronic devices. Structural and optical characterizations were carried out by scanning electron microscopy, atomic force microscopy, and optical transmission spectroscopy. We show that the properties of the ZnO nanostructured films depend strongly on the type of primary oxide-covered substrate used. Previous studies on different electrodeposition methods for nucleation and growth are considered in the final discussion.We thank Prof. A. Segura of the Universitat de Valencia for the facilities with the sputtering equipment. This work was supported by the project PROMETEO/2009/074 from the Generalitat Valenciana.Reyes Tolosa, MD.; Damonte, LC.; Brine, H.; Bolink, HJ.; Hernández Fenollosa, MDLÁ. (2013). Nucleant layer effect on nanocolumnar ZnO films grown by electrodeposition. Nanoscale Research Letters. 8:135-144. https://doi.org/10.1186/1556-276X-8-135S1351448Franklin JB, Zou B, Petrov P, McComb DW, Ryanand MP, McLachlan MA,J: Optimised pulsed laser deposition of ZnO thin films on transparent conducting substrates. Mater Chem 2011, 21: 8178–8182. 10.1039/c1jm10658aJaroslav B, Andrej V, Marie N, Šuttab P, Miroslav M, František U: Cryogenic pulsed laser deposition of ZnO. 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