Towards More Efficient Solar Cells: the Effect of Dynamical Disorder on the Electronic Structure of Halide Double Perovskites

Abstract

Recently, simple perovskites have attracted great attention as energy-absorbing materials in solar cells. In computational and experimental studies they have shown several desirable properties but also challenges, such as instabilities and toxicity due to the presence of heavy metals, such as lead. As a solution to the problems connected to the simple perovskites, the double perovskites were suggested as suitable materials in the solar cells of tomorrow. In order to use double perovskites in an application they need to be thoroughly understood. Within this thesis the octahedral tilting and the band gap of double perovskites have been studied, which is a step towards finding a material that is stable and exhibit the optimal band gap for absorbing solar energy. It turns out that the octahedral tilting is not as prominent in all double perovskites as in the simple ones. The statement that the octahedral tilting is due to the presence of lone-pair electrons is considered and it agrees with the calculations - lone-pair electrons induce octahedral tilting. The effect of octahedral tilting on the band gap of the double perovskites is studied as well and it is concluded that the band gap increases with the tilting. So, as the global warming increases rapidly it is important to find green solutions and as solar cells produce renewable energy and are emission-free they are good candidates for further research and developement.