Styrning av gradienter i tunnfilmssolceller

Research Project, 2016 – 2021

This project aims at the development of annealing processes in sulfur, selenium or other vapors, for higher efficiency thin film solar cells based on Cu(In,Ga)Se2 and Cu2ZnSnS4. The specific aim is to make band gap graded films both at the back- and front interfaces for reduced solar cell losses. The starting material can be either graded or non-graded, and is deposited by co-sputtering or co-evaporation. A custom-built furnace, with three sources, where temperature and partial pressure can be separately controlled, is used. The third source can for example be used for Na- or Ka-based compounds for surface modifications. The process development, including fabrication, analysis and modeling of solar cell devices, is accompanied by fundamental studies of inter-diffusion, phase segregation, homogeneity and grain growth in these material systems. Large area depth profiling measurements are complemented by local characterization by atom probe tomography. Theoretical analysis by first-principles based methods is used to study properties such as phase stability, electronic structure, defect and cluster formation and grain boundary properties. Diffusion studies are supported by molecular dynamics simulations. The expected outcome is processes for increased device efficiency for these solar cells, or maintained efficiency with processes better suited for industrial processing. This is based on better understanding of fundamental limitations set by thermodynamic and kinetic concerns.