Silicon Grain Boundaries: Correlated Chemical and Electro-Optical Characterization

The interrelationships among the chemistry, composition, and the electrooptical properties of grain boundaries and the performance of polycrystalline Si solar cells are examined. Two impurity mechanisms are reported. The first is the segregation of oxygen to the grain boundaries during thermal processing of the materials/devices. Direct evidence is presented relating the grain boundary oxygen content to the electrical activation of that region. The second is the passivation of the grain boundaries by hydrogen incorporation. The first direct evidence for hydrogen penetration down grain boundaries (correlated with electrical characteristics) is presented. A new method is introduced utilizing the volume indexing of digital SIMS signals, providing compositional information and impurity maps on internal materials/device interfaces.