Photovoltaic (PV) cells directly convert sunlight into electrical energy without the emission of carbon dioxide or other pollutants. That's the reason why they have been in the news for some time now. Over the years, there has been significant progress in making PV cells and modules more efficient, pushing the performance of the world-leading PV material silicon to reach its theoretical efficiency limit. Various concepts for further increasing the power conversion efficiency of PV cells were developed among them so-called tandem solar cells made up of two materials with different absorption characteristics that in combination convert a higher share of the incident sunlight to electricity. From a technological perspective, it is highly interesting to integrate a second PV material into the well-established Si-based process chain to enable fast market penetration through mass production. The requirements for such a material are non-toxicity, long-term stability, high conversion efficiency, compatibility with Si, consisting of non-critical, abundant raw materials, low thermal and energy budget in fabrication, etc.
In this project, nickelate perovskites are investigated as an alternative to the highly efficient but poorly stable halide perovskites. Nickelates, being oxide-perovskites, are stable under environmental conditions and exhibit resistance to photobleaching and thermal exposure. Typically, oxide-perovskites have ABO3 chemical formula, where A and B are cations bound to oxygen as an anion. In this work, various abundant and non-toxic rare-earth elements will be incorporated on the A-site and nickel will occupy the B-site. Since there is limited data on nickelates for PV applications, this research work aims to fill those gaps. We will investigate, eg, the bandgap energy for the different A-site cations to determine the most promising composition for PV applications.
The perovskite films will be explored by combinatorial material synthesis, here combinatorial pulsed laser deposition, that allows rapid screening of different cation compositions. Characterization tools like, x-ray diffraction (XRD) gave information about the structure and crystallinity, x-ray fluorescence (XRF) and x-ray photoelectron spectroscopy (XPS) about the composition, ellipsometer about the thickness and refractive index, and ultraviolet- visible spectroscopy about the absorption edge of the deposited films. The optimal composition discovered will then be grown with a minimal energy budget using easily scalable low-temperature atomic layer deposition.