Design, Synthesen und Charakterisierung von n-Typ-Metalloxidhalbleitern als Interfacematerialien für (opto)-elektronische Bauelemente

Over the past few years, there have been a large number of efforts on wetchemical synthesis of semiconductor metal oxide nanoparticles (MeOxNPs) and metal oxide precursor solutions (sMeOx) due to their decisive role in research and development of new materials and devices. The main goal of the novel synthetic routes is and remains the development of new synthesis strategies and production methods for MeOx NPs and sMeOx allowing one to precisely predict the composition, structure, size and opto‐electronic properties. In this regard in‐depth studies of synthesis and product characterizations are an important step towards more new technological applications. In the present work various sol‐gel techniques, which should help preparation and processing of undoped and doped n‐type metal oxide semiconductor materials (ZnO NPs, Zn1‐xAlxO NPs, Zn1‐xCoxO NPs, Zn1‐xNixO NPs, Al3+ doped ZnO (sAZO), TiO2 NPs, LixTi1‐xO2 NPs) in the nanometer range, are slightly modified and performed. In order to find and to optimize a simple, cost‐effective, environmentally friendly and efficiently synthetic route the advantages and disadvantages of applied sol‐gel methods are in detail discussed and compared. Additionally, the reaction mechanisms which provide important and in‐depth insights in the formation of synthesized undoped and doped ZnO NPs, TiO2 NPs and sAZO are thoroughly analyzed. Using a wide range of characterization methods (UV‐Vis spectroscopy, XRD, SEM, TEM, FTIR spectroscopy, PL spectroscopy, Raman spectroscopy) and measurement techniques (Kelvin probe (WF), conductivity (σ)), the structural, morphological and opto‐electronic properties of produced n‐type metal oxide semiconductors (ZnO NPs, Zn1‐xAlxO NPs, Zn1‐xCoxO NPs, Zn1‐xNixO NPs, Al3+ doped ZnO (sAZO), TiO2 NPs, LixTi1‐xO2 NPs) in both bulk and thin transparent films are investigated and tested. The aim of those investigations is to gain sufficient information concerning the integration of synthesized binary metal oxides (ZnO NPs, Zn1‐xAlxO NPs, Zn1‐xCoxO NPs, Zn1‐xNixO NPs, Al3+ doped ZnO (sAZO), TiO2 NPs, LixTi1‐xO2 NPs) as interface materials or as intermediate layers in inverted organic BHJ solar cells (ioBHJ). According to achieved experimental results, the produced interfacial layers via doctor blading based on synthesized n‐type‐metal oxide semiconductor nanomaterials (ZnO NPs, Zn1‐xAlxO NPs, Zn1‐xCoxO NPs, Zn1‐xNixO NPs, Al3+ doped ZnO (sAZO), TiO2 NPs, LixTi1‐xO2 NPs) can satisfy even the most requirements for interface layers. They possess large band gaps (Eg) and the transmission (%T) of all thin transparent films in the visible range is more than ≥ 85%. The differences in the measured work functions (WF) are also not so much. The compared conductivity (σ) values confirmed that selected synthesis method and the applied coating technology can play an important role by producing thin interfacial metal oxide films with suitable physical and chemical properties. A direct comparison of synthesized (ZnO NPs, Zn1‐xAlxO NPs, Zn1‐xCoxO NPs, Zn1‐xNixO NPs, Al3+ doped ZnO (sAZO), TiO2 NPs, LixTi1‐xO2 NPs) as electron extraction layers or electron transport layers in ioBHJ solar cells provides that Al3+ doped ZnO precursor solutions (HT‐AZO or LT‐AZO) are in advantage towards particulate dispersions based on ZnO NPs. They have more compact and dense layers which include relatively good conductivity (σ) and higher transmission (%T). By the variation of their layer thickness no perceptible influence on the performance of ioBHJ solar cells are observed, compared to interfacial layers based on ZnO NPs. In addition, it is determined that TiO2 NPs and LixTi1‐xO2 NPs interface layers allow the construction of reproducible and efficiently ioBHJ solar cells and therefore they prove to be a good alternative for replacement of interface layers based on ZnO NPs. However, development and fabrication of efficient ioBHJ solar cells require intensive stability tests. The most significant studies up to now focus on fundamental degradation mechanisms of organic semiconductors, but not on the degradation behavior of metal oxide interfacial layers (MeOx NPs, sMeOx). In this regard, the effect of temperature, adsorption of oxygen (O2), diffusion of moisture or moisture vapor and UV‐light on the optical and electrical properties of metal oxide thin films (HT‐AZO or LT‐AZO) by applying damp heat test and UV radiation test were investigated and correlated to device degradation. The achieved experimental results show that the optical properties like transmittance (%T) and band gap (Eg) are not influenced by damp heat test and UV radiation test. It is recognized that the electrical properties of both HT‐ and LT‐AZO thin films, i.e. work function (WF) and conductivity (σ) showed evident degradation upon damp heat exposure indicating the strong interaction between the metal oxide surface and the ambient conditions leading to the formation of a depletion layer. Accelerated device degradation under damp heat testing underlines the formation of a barrier or depletion layer at the interface, reducing VOC, JSC, and FF.Metalloxide als transparente Leiter gewinnen immer mehr an Bedeutung bei der Entwicklung innovativer, maßgeschneiderter und anwendungsorientierter Lösungen für viele zukünftige Schlüsseltechnologien, etwa im Bereich der Energieumwandlung (Photovoltaik), gedruckten organischen Nanoelektronik, neuen Beleuchtungssystemen und Oberflächenbeschichtungen (Touchscreens). Die folgende Dissertation behandelt die Durchführung und Optimierung der Syntheseverfahren von Metalloxid-basierten Nanomaterialien (MeOx) mit spezifischen Funktionalitäten. Dazu schafft eine Reihe von Charakterisierungsmethoden und Messtechniken einen vollständigen Ausblick in der Struktur, Morphologie und chemischen Zusammensetzung dieser Halbleitermetalloxid-Materialien. Im Mittelpunkt stehen bewusst die anwendungsbezogenen Eigenschaften der hergestellten Metalloxide im Nanometerbereich und die Voraussetzungen, die sie als Interfacematerialien erfüllen müssen. Gedruckt auf Glas oder Folie weisen sie hohe optische Transparenz, einstellbare elektrische Leitfähigkeit, Flexibilität und Kosteneffizienz auf. Ihre Integrierung als dünne Extraktions- und Transportschichten (Interface-Elektroden) in der organischen Photovoltaik und die Analyse ihres Zersetzungsverhaltens führen zur Entwicklung und Realisierung stabiler und hocheffizienter organischer BHJ Solarzellen

Design, syntheses and characterization of n-type metal oxide semiconductors as interface materials for opto-electronic devices

Metalloxide als transparente Leiter gewinnen immer mehr an Bedeutung bei der Entwicklung innovativer, maßgeschneiderter und anwendungsorientierter Lösungen für viele zukünftige Schlüsseltechnologien, etwa im Bereich der Energieumwandlung (Photovoltaik), gedruckten organischen Nanoelektronik, neuen Beleuchtungssystemen und Oberflächenbeschichtungen (Touchscreens). Die folgende Dissertation behandelt die Durchführung und Optimierung der Syntheseverfahren von Metalloxid-basierten Nanomaterialien (MeOx) mit spezifischen Funktionalitäten. Dazu schafft eine Reihe von Charakterisierungsmethoden und Messtechniken einen vollständigen Ausblick in der Struktur, Morphologie und chemischen Zusammensetzung dieser Halbleitermetalloxid-Materialien. Im Mittelpunkt stehen bewusst die anwendungsbezogenen Eigenschaften der hergestellten Metalloxide im Nanometerbereich und die Voraussetzungen, die sie als Interfacematerialien erfüllen müssen. Gedruckt auf Glas oder Folie weisen sie hohe optische Transparenz, einstellbare elektrische Leitfähigkeit, Flexibilität und Kosteneffizienz auf. Ihre Integrierung als dünne Extraktions- und Transportschichten (Interface-Elektroden) in der organischen Photovoltaik und die Analyse ihres Zersetzungsverhaltens führen zur Entwicklung und Realisierung stabiler und hocheffizienter organischer BHJ Solarzellen.Over the past few years, there have been a large number of efforts on wetchemical synthesis of semiconductor metal oxide nanoparticles (MeOxNPs) and metal oxide precursor solutions (sMeOx) due to their decisive role in research and development of new materials and devices. The main goal of the novel synthetic routes is and remains the development of new synthesis strategies and production methods for MeOx NPs and sMeOx allowing one to precisely predict the composition, structure, size and opto‐electronic properties. In this regard in‐depth studies of synthesis and product characterizations are an important step towards more new technological applications. In the present work various sol‐gel techniques, which should help preparation and processing of undoped and doped n‐type metal oxide semiconductor materials (ZnO NPs, Zn1‐xAlxO NPs, Zn1‐xCoxO NPs, Zn1‐xNixO NPs, Al3+ doped ZnO (sAZO), TiO2 NPs, LixTi1‐xO2 NPs) in the nanometer range, are slightly modified and performed. In order to find and to optimize a simple, cost‐effective, environmentally friendly and efficiently synthetic route the advantages and disadvantages of applied sol‐gel methods are in detail discussed and compared. Additionally, the reaction mechanisms which provide important and in‐depth insights in the formation of synthesized undoped and doped ZnO NPs, TiO2 NPs and sAZO are thoroughly analyzed. Using a wide range of characterization methods (UV‐Vis spectroscopy, XRD, SEM, TEM, FTIR spectroscopy, PL spectroscopy, Raman spectroscopy) and measurement techniques (Kelvin probe (WF), conductivity (σ)), the structural, morphological and opto‐electronic properties of produced n‐type metal oxide semiconductors (ZnO NPs, Zn1‐xAlxO NPs, Zn1‐xCoxO NPs, Zn1‐xNixO NPs, Al3+ doped ZnO (sAZO), TiO2 NPs, LixTi1‐xO2 NPs) in both bulk and thin transparent films are investigated and tested. The aim of those investigations is to gain sufficient information concerning the integration of synthesized binary metal oxides (ZnO NPs, Zn1‐xAlxO NPs, Zn1‐xCoxO NPs, Zn1‐xNixO NPs, Al3+ doped ZnO (sAZO), TiO2 NPs, LixTi1‐xO2 NPs) as interface materials or as intermediate layers in inverted organic BHJ solar cells (ioBHJ). According to achieved experimental results, the produced interfacial layers via doctor blading based on synthesized n‐type‐metal oxide semiconductor nanomaterials (ZnO NPs, Zn1‐xAlxO NPs, Zn1‐xCoxO NPs, Zn1‐xNixO NPs, Al3+ doped ZnO (sAZO), TiO2 NPs, LixTi1‐xO2 NPs) can satisfy even the most requirements for interface layers. They possess large band gaps (Eg) and the transmission (%T) of all thin transparent films in the visible range is more than ≥ 85%. The differences in the measured work functions (WF) are also not so much. The compared conductivity (σ) values confirmed that selected synthesis method and the applied coating technology can play an important role by producing thin interfacial metal oxide films with suitable physical and chemical properties. A direct comparison of synthesized (ZnO NPs, Zn1‐xAlxO NPs, Zn1‐xCoxO NPs, Zn1‐xNixO NPs, Al3+ doped ZnO (sAZO), TiO2 NPs, LixTi1‐xO2 NPs) as electron extraction layers or electron transport layers in ioBHJ solar cells provides that Al3+ doped ZnO precursor solutions (HT‐AZO or LT‐AZO) are in advantage towards particulate dispersions based on ZnO NPs. They have more compact and dense layers which include relatively good conductivity (σ) and higher transmission (%T). By the variation of their layer thickness no perceptible influence on the performance of ioBHJ solar cells are observed, compared to interfacial layers based on ZnO NPs. In addition, it is determined that TiO2 NPs and LixTi1‐xO2 NPs interface layers allow the construction of reproducible and efficiently ioBHJ solar cells and therefore they prove to be a good alternative for replacement of interface layers based on ZnO NPs. However, development and fabrication of efficient ioBHJ solar cells require intensive stability tests. The most significant studies up to now focus on fundamental degradation mechanisms of organic semiconductors, but not on the degradation behavior of metal oxide interfacial layers (MeOx NPs, sMeOx). In this regard, the effect of temperature, adsorption of oxygen (O2), diffusion of moisture or moisture vapor and UV‐light on the optical and electrical properties of metal oxide thin films (HT‐AZO or LT‐AZO) by applying damp heat test and UV radiation test were investigated and correlated to device degradation. The achieved experimental results show that the optical properties like transmittance (%T) and band gap (Eg) are not influenced by damp heat test and UV radiation test. It is recognized that the electrical properties of both HT‐ and LT‐AZO thin films, i.e. work function (WF) and conductivity (σ) showed evident degradation upon damp heat exposure indicating the strong interaction between the metal oxide surface and the ambient conditions leading to the formation of a depletion layer. Accelerated device degradation under damp heat testing underlines the formation of a barrier or depletion layer at the interface, reducing VOC, JSC, and FF

Development of Efficient and Stable Inverted Bulk Heterojunction (BHJ) Solar Cells Using Different Metal Oxide Interfaces

Solution-processed inverted bulk heterojunction (BHJ) solar cells have gained much more attention during the last decade, because of their significantly better environmental stability compared to the normal architecture BHJ solar cells. Transparent metal oxides (MeOx) play an important role as the dominant class for solution-processed interface materials in this development, due to their excellent optical transparency, their relatively high electrical conductivity and their tunable work function. This article reviews the advantages and disadvantages of the most common synthesis methods used for the wet chemical preparation of the most relevant n-type- and p-type-like MeOx interface materials consisting of binary compounds AxBy. Their performance for applications as electron transport/extraction layers (ETL/EEL) and as hole transport/extraction layers (HTL/HEL) in inverted BHJ solar cells will be reviewed and discussed

Inverted organic solar cells using a solution processed aluminum-doped zinc oxide buffer layer

In this article, we demonstrate a route to solve one of the big challenges in the large scale printing process of organic solar cells, which is the reliable deposition of very thin layers. Especially materials for electron (EIL) and hole injection layers (HIL) (except poly(3,4-ethylene dioxythiophene):(polystyrene sulfonic acid) (PEDOT:PSS)) have a low conductivity and therefore require thin films with only a few tens of nanometers thickness to keep the serial resistance under control. To overcome this limitation, we investigated inverted polymer solar cells with an active layer comprising a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) with solution processed aluminum-doped zinc oxide (AZO) EIL. Devices with AZO and intrinsic zinc oxide (i-ZnO) EIL show comparable efficiency at low layer thicknesses of around 30 nm. The conductivity of the doped zinc oxide is found to be three orders of magnitude higher than for the i-ZnO reference. Therefore the buffer layer thickness can be enhanced significantly to more than 100 nm without hampering the solar cell performance, while devices with 100 nm i-ZnO films already suffer from increased series resistance and reduced efficiency. (C) 2011 Elsevier B.V. All rights reserved

Comparison of various sol-gel derived metal oxide layers for inverted organic solar cells

Inverted bulk-heterojunction solar cells have recently captured high interest due to their environmental stability as well as compatibility to mass production. This has been enabled by the development of solution processable n-type semiconductors, mainly TiO(2) and ZnO. However, the device performance is strongly correlated to the electronic properties of the interfacial materials, and here specifically to their work function, surface states as well as conductivity and mobility. It is noteworthy to say that these properties are massively determined by the crystallinity and stoichiometry of the metal oxides. In this study, we investigated aluminum-doped zinc oxide (AZO) as charge selective extraction layer for inverted BHJ solar cells. Thin AZO films were characterized with respect to their structural, optical and electrical properties. The performance of organic solar cells with an AZO electron extraction layer (EEL) is compared to the performance of intrinsic ZnO or TiO(x) EELs. We determined the transmittance, absorbance, conductivity and optical band gap of all these different metal oxides. Furthermore, we also built the correlations between doping level of AZO and device performance, and between annealing temperature of AZO and device performance. (C) 2011 Elsevier B.V. All rights reserved