Point defects and their impact in next generation solar cells revealed by in-situ positron annihilation spectroscopy

Positron Annihilation Spectroscopy (PAS) is a very sensitive method to reveal the presence of vacancy-related point defects in thin film solar cells. Its depth-range and resolution matches various types of existing and emerging thin film solar cells. We apply Positron annihilation spectroscopy (PAS) to monitor environmental degradation of ZnO/CIGS and of perovskite solar cells. Furthermore, we examine the presence of point defects and near-surface oxidation of thermally annealed RF-sputtered BaSi2 thin films. We show that the positron is a very sensitive probe for the surfaces of semiconductor quantum dots in thin film QD photovoltaic systems. Ab-initio modelling in combination with Positron Annihilation Lifetime Spectroscopy (PALS) provided first-time proof of the presence of the positron surface state underlying the very high sensitivity of positrons to probe surfaces of CdSe quantum dots.