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Novel Composite Oxides by Combinatorial Material Synthesis for Next Generation All-Oxide-Photovoltaics

Periodic Report Summary 1 - ALLOXIDEPV (Novel Composite Oxides by Combinatorial Material Synthesis for Next Generation All-Oxide-Photovoltaics)

Project Context and Objectives:
Energy policies increasingly push for innovative technologies such as solar energy Photovoltaic (PV) conversion devices, to decrease polluting emissions and reduce global climate change. However, despite the constant reduction in the cost of photovoltaic systems, mainly in the areas of module production, electronics and shipment, the significant cost of cell materials and fabrication have not been sufficiently reduced. To meet grid-parity, a cost reduction breakthrough using cheap abundant materials, in conjunction with low cost, disperse fabrication methods and long service time, is required.

The main objective of this AllOxidePV project is to develop low cost All-Oxide photovoltaic cells and modules, as the basis for next generation, low-cost, durable photovoltaic systems, enabling grid-parity worldwide. Metal oxides (MOs) were chosen as the desired family of materials for PV devices, as they are chemically stable, mostly non-toxic, abundant and can be manufactured in low cost methods under ambient conditions. Devices made of oxide semiconductors are mostly inexpensive, very stable and environmentally safe, (three most important requirements for photovoltaics). Unfortunately, most known MOs are not suitable active solar cell materials due to their electronic properties i.e. short lifetime and low mobility of electronic charge carriers. The development of new, multi-component MOs, including doped oxides, new crystal structures, amorphous materials and composites, lies at the heart of the AllOxidePV project. The goal is to overcome the limiting properties of known oxides, enabling efficient, durable solar conversion to electricity at an extremely low cost.

An interdisciplinary approach, merging combinatorial material science, interface engineering, analytical nanoscience, spectroscopy and computational data analysis, together with smart engineering of the internal surfaces and interfaces for these solar cells, will enable the realization of the AllOxidePV project and its challenging and ambitious goals. The project also involves multiple feedback loops between synthesis, characterization and device performance, accompanied by fundamental studies on highly idealized systems, for the understanding of the underlying physics.

The new PV family fabricated by our project's partners from low cost, durable and stable materials with inexpensive, ambient, large scale deposition methods, aims at making the required breakthrough in solar energy conversion science, technology, and cost. To achieve this goal we define the following objectives:
• Development of composite MOs with novel functionalities using combinatorial material synthesis
• High-throughput characterization of innovative MOs for All-Oxide photovoltaics
• Synthesis and characterization of well-defined model systems to gain an understanding of underlying physics for further material development
• Device design, fabrication and testing based on computational data mining
• Development of low-cost all-oxide PV fabrication technologies based on spray pyrolysis, bath deposition and combustion synthesis by spin coating.

The technologies applied, include:
• Combinatorial Material Science developing new MOs for the All Oxide PV.
1) High throughput material synthesis, generating a large variety of promising new composite oxides within a single deposition process.
2) High throughput detailed characterization of structural, optical and electronic properties (scanning XRD, transmission, reflection, scattering, impedance spectroscopy, conductivity).
3) Computational data storing and data mining including a dedicated database for experimental data from all groups and unique data mining processes to identify directions of progress.
• Synthesis of a highly ordered model systems to investigate the underlying physics of composites.
• In situ characterization of MO surfaces and interfaces during deposition
• Detailed characterization of promising new composite oxides and highly idealized model systems to gain an understanding of underlying physics and to derive design rules for suitable PV MO composites.
• Amorphous oxide electronics
• Transparent conducting oxides
• Development of large area fabrication tools and deposition techniques for process up scaling and mass production of MO-based PVs.

The consortium is comprised of the following research groups:
• Combinatorial Materials Science Laboratory, Bar Ilan University (BIU), Israel
• The Inorganic Materials Science (IMS) group of the MESA+ Institute for Nanotechnology, University of Twente (UT), Netherlands
• The Group of Photovoltaic and Optoelectronic Devices of the Physics Department, University Jaume I (UJI), Spain
• The Surface Science Division of the Materials Science Department, Darmstadt University of Technology (DUT), Germany
• CENIMAT - Centre for Materials Research, Department of Materials Science, FCT, Universidade Nova de Lisboa (UNI), Portugal
• SolMateS B. V. (SOL), Netherlands

In summary, the project's main objective is to develop new metal oxide, with new properties for realizing a new generation of efficient, durable, low cost PV family, all-oxide, photovoltaics.
Project Results:
The AllOxidePV project includes 7 work packages (WPs):
(1) Combinatorial Material Synthesis
(2) High-Throughput Characterization
(3) Modelling Systems' Physics
(4) All-Oxide Solar Cell Fabrication
(5) Fabrication process up scaling
(6) Coordination, dissemination & exploitation
(7) Management.

During the first 18 months, all partners attained significant progress and encouraging results and met all goals and milestones. PV cell efficiency improved from 0.020% to 0.23%, indicating feasibility for defining a new generation of low-cost PV cells via Combinatorial Materials Science.
The partners collaborated utilizing ongoing data and staff exchanges between groups.
Prof. Ichiro Takeuchi (USA) was appointed to the project's professional advisory board and a website was launched for partner and public use. The project was presented worldwide in lectures, presentations and posters, in leading conferences.
Summary of work and achievements during the first 18 months is as follows:

Partners have improved their facilities and developed new infrastructures, concepts and methods.

The DUT Surface Science Group has, for example, set up facilities for co-sputtering oxides at the DAISY-MAT. Deposition of Bi-Mn and Bi-Ni Oxides have been studied, and Mn Targets were found unstable. While Bi- and Ni oxides are transparent, the mixed oxides are highly absorbing.

BIU strengthened its CMS capabilities and developed new PV combinatorial device concepts, including window layers, light absorbers, back contacts, etc. High-throughput fabrication tools were developed and include PLD, Sequential Spray Pyrolysis (SP), and a new advanced sputtering station with varying plume location, 6 guns and 4 deposition sources.

High-throughput scanning characterization tools were developed that include a conductivity and photoconductivity scanner, thickness measurement, fast Impedance Spectroscopy scanner and PV performance setup for scanning small area PV cells in light and in dark.

Related high-throughput analysis techniques were developed, that include optical analyses, absorption, thicknesses, band-gap analysis combining optical and thickness data, composition mapping, electrical conductivity, crystallography, polymorphs, photocurrent, IV curves under solar simulation and in dark, Internal Quantum Efficiency etc.

A materials and devices database was developed to collect of the deposition, characterization and analytical information in near real-time.

BIU, DUT, UNI, UJI and UT synthesized and characterized new MO compounds/devices, exploring their potential as absorber layers in all-oxide-PV devices. New characteristics such as electrical resistivity (ρ), transport properties, bandgap values, band alignment, crystal structures and spectral response were found which might lead to their use as light absorbers in PV cells. Many composite materials with varying atomic ratios yielded interesting properties of relevance showing the significant effect of material complexity. Further XRD, Raman and UV-Vis spectra measurements, and hierarchical clustering analyses such as with Fe2O3-Nb2O5, showed distinct spectral behavior, indicating different structures and physical properties for potential PV devices. Most of these MOs will be explored by tuning of compound composition, growth conditions and crystal morphology.

A strategy for tailoring band gaps and interfacial barriers of functional oxides was developed by DUT, including the study of empirical design rules for predicting EVB and ECB of binary and ternary composites.

UT, DUT and additional partners have investigated fabrication of several highly ordered oxide-oxide interfaces.

Fabrication-process up scaling was studied by UNI, UT and SolMateS. SolMateS up-scaled MO solutions developed by UT in this project, using PLD. During the 18mo period, SolMateS developed (1) an industrial PLD for thin films on substrates (200mm diameter), (2) a room temperature process for a transparent conductive oxide layer on glass via PLD , Indium Tin Oxide (ITO) PLD deposition with excellent film properties (TR> 85% @VIS range). This transparent conductive oxide layer on glass is ready for industrial process, with very short deposition time (1min/100mm wafers).

FTO/c-TiO2/Cu:Co3O4 heterojunction solar cells were fabricated by UNI via Spray Pyrolysis (SP), optimized and are still under characterization. The structural, optical and electrical properties of the films and cells have been characterised with various techniques including x-ray diffraction, hall effect measurement, UV-Vis-NIR spectroscopy, dark and photo-conductivity, AFM and SEM.

Potential Impact:
Conventional energy sources based on oil, coal, and natural gas have proven to be highly effective drivers of economic progress, but at the same time damaging to the environment and to human health. Energy policies increasingly push for innovative technologies such as solar energy Photovoltaic (PV) conversion devices to decrease polluting emissions and reduce global climate change. However, in the case of photovoltaic systems, the cost of cell materials and fabrication have not been sufficiently reduced for large-scale use to meet grid-parity. A cost reduction breakthrough using cheap, abundant materials in photovoltaic systems, in conjunction with low-cost fabrication methods is required.

The main objective of this AllOxidePV project is to develop low cost All-Oxide photovoltaic cells and modules, as the basis for future next generation, low-cost photovoltaic systems, enabling grid-parity worldwide.

The new PV family fabricated by our project's partners from low cost, stable materials with inexpensive, ambient, large scale deposition methods, aims at making the required breakthrough in solar energy conversion science, technology, and cost.

The cost reduction of photovoltaic systems, the direct expected outcome of the AllOxidePV project, and a related increase in the use of photovoltaics worldwide, has significant social, economic and environmental impacts on humanity. Solar energy conversion systems generating power and electricity for homes, buildings and cities, maximize the use of earth's resources, help conserve energy, avoid pollution and make the world cleaner and thus healthier. The extended use of PV systems will also slow down the global warming, reduce the dependency in oil and its traditional suppliers, and create significant amounts of new jobs worldwide.

Health Improvement by Green / Sustainable Energy - Generating energy from solar panels emits very little pollution into the air, and thus solar energy is a much cleaner source of energy than burning fossil fuels. Cities or areas that decide to extensively use solar energy to power buildings would enjoy a higher quality of air in the region, which in turn can make sure citizens and workers in the area are healthier. Furthermore, studies indicate that burning fossil fuels facilitates global warming. Solar panels emit very low amounts of hazardous pollution into the air, and so solar energy does not damage the atmosphere or cause global warming. If areas decide to use solar energy to generate electricity, the shift will help diminish the effects of global warming, such as the sea levels rising and storms intensifying.

Job Creation - When cities or companies build and operate solar energy facilities, the projects often help to create jobs in project planning, development and implementation, constructing solar energy plants, managing equipment and operating the facility. These new job opportunities do not replace or typically come at the expense of any existing conventional energy related jobs, and decrease the unemployment rate of the given area.

Energy Independence Instead of Oil Dependence – Countries and utilities that burn fossil fuels to generate energy and power for homes and businesses, rely on oil to generate energy. As a result, they become dependent on oil that often comes from foreign nations to create the electricity. Therefore, solar energy programs and policies would help reducing the amount of oil purchased from foreign nations, reducing the dependence on foreign oil supplying countries.

Economics - Manufacturing solar energy is already, in many parts of the world, less expensive than burning fossil fuels, which is the traditional method of generating electricity. Thus, if businesses or households decide to use solar energy to power electricity in their homes or buildings, their electric bills can be substantially less than if they use energy generated from fossil fuels. Over an extended period, the financial difference of cheaper electric bills can become quite significant, enabling families and businesses to inject more of their money into the economy.

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