PhD Defense of Raphael FILLON

This PhD work aims at studying the electronic properties of thin films CZTSSe solar cells. The final purpose is to identify crystallographic defects and determine their influence on the solar cells behavior in order to improve the efficiency and make CZTSSe competitive with other thin film technologies.
The first part of the work deals with the fabrication of the CZTSSe thin films and solar cells. CZTSSe is synthetized using a two-step process: vacuum deposition of precursors followed by an annealing under selenium atmosphere. The second part of the PhD work is the electrical characterization of the cells in the dark. Capacitance versus voltage measurements and admittance measurements are carried out at different temperatures. The results cannot be fully explained by usual models. As a consequence, further analysis has been conducted in a third part. Admittance has been calculated based on the classical equations that describe charge carriers in semi-conductor. The first interpretation only takes into account the contribution of defects. When the influence of potential fluctuations is added to the model, the adjustment between experimental measurements and calculated data is improved. However, a third component has to be included to fit the CZTSSe dielectric response. This component, causing a power variation of the conductivity with frequency is related to hopping mechanism. Adding this contribution to the admittance calculation allows to show that the CZTSSe conductivity is dominated by a localized states transport and can explain the low conductivity value .