Speaker
Description
Photovoltaic (PV) installations have recently reached the terawatt level and this is almost entirely due to the success of silicon-based solar cell technologies. Silicon PV is low-cost and cell efficiencies are unrivalled by other mass-market single-junction technologies. Improvements in silicon cells will have a real-world impact on climate change mitigation and improving energy supply security.
Hydrogen-related defect engineering is fundamental for several processes in the photovoltaics industry. It is involved in the fabrication of anti-reflection coatings and in the passivation of surface and bulk carrier traps. However, hydrogen has also been blamed for being involved in the degradation of the conversion efficiency of Si solar cells (by up to 16% relative after several months/years of sun-light exposure in the field). This is known as Light and elevated Temperature Induced Degradation (LeTID) of the cells, and it is manifested as a severe life-time reduction of photo-generated electrons which are trapped and annihilated at unknown defects in the silicon.
We present a hybrid density functional study of thermally- and carrier-activated processes involving reactions between hydrogen and group-III acceptors in crystalline silicon. Finite-temperature calculations of the free energy change along the reactions, allow us to come up with a first-principles-level account of the degradation mechanism of the cells, as well as possible routes for avoiding LeTID.
Our findings have important repercussions regarding our understanding of hydrogen in p-type silicon, its role on doping and lifetime of carriers.
