Characterization of the solar cell materials using surface spectroscopy techniques

Most solar cells fabricated using earth abundant materials are based on heterojunction architecture since their doping to form p-n junctions is quite challenging. Therefore, band alignment engineering by impurity management is critical for the performance of heterojunction thin film solar cells. In this thesis, the interfaces between different layers within various solar cell compositions are studied by ultraviolet photoelectron spectroscopy (UPS) determine the valence band alignment and therefore to engineer better electron and hole transport layers. Additionally, time of flight secondary ion mass spectroscopy (TOF-SIMS) studies will be carried out to measure the impurity levels in various (Perovskit) active layers of the solar cells, and the effect of impurity level to the valence band maximum are investigated. Elemental concentrations and chemical compositions of various layers are investigated using X-ray photoelectron spectroscopy (XPS) depth profiling technique. UPS and XPS are performed complementarily to measure the valence band maximum more precisely. Finally, band gap of the target materials are measured via optical reflection and transmission measurements. Bant gap information and the valence band maximum value will be used to obtain the conduction band alignment and therefore in designing superior electron transport layers. This thesis will allow the fabrication of heterojunction solar cells with near-perfect band alignment.