Study of highly efficient $Cu(In,Ga)Se_2$ thin film-based tandem solar cells: alkali incorporation and compositional profile modification

Abstract

In this thesis, the efficiencies of $Cu(In,Ga)Se_2$ (CIGS) thin film solar cells are improved by technical engineering such as alkali incorporation and modification of compositional gradient of CIGS absorbing material. This work also includes characterizations of both material and devices for unveiling and regulating the loss or gain mechanisms of optical and electrical properties or resulting performance. The effects of unexplored heavy-alkali doping onto CIGS absorbers are revealed, especially the influence on deep-level defects inside the material and the consequent enhancement of the solar devices. Diffusion of heavy alkali element in CIGS is investigated in order to discover how such large atoms are distributed inside the films. Furthermore, the impact of alkali incorporation into different bandgap profiles of the material is examined, specifically operating behavior of the devices. These accomplishments are finally expanded to tandem applications to surmount the performance of single CIGS solar cells. This thesis presents state-of-the-art perovskite/CIGS tandem solar cell and provide a guidance for future developments.