Muon spin spectroscopy to probe depth-dependent carrier lifetimes in silicon photovoltaics

Crystalline silicon is used for >90% of photovoltaic solar cells. Electron-hole pairs are produced when light of certain frequencies is absorbed. Some of these charge carriers are lost due to recombination processes in the silicon before they are collected, and the lifetime (or diffusion length) of the carriers defines the quality of a silicon wafer. A new ISIS-developed muon spin spectroscopy technique has advantages over incumbent methods as it is possible to: (i) implant the muon beam to different depths to give depth-dependent lifetime; and (ii) implant muons through metallic layers to enable lifetimes to be measured in completed cells. Our objectives are to use this technique to: (i) separate bulk- and surface-related recombination; (ii) understand passivation activation annealing processes; and (iii) make the first direct lifetime measurements in completed silicon cells.