Lock-in EBIC studies of CdS/CdTe solar cells grown by high vacuum evaporation

The use of an electostatically blanked electron beam has allowed the application of phase sensitive detection to the electron beam-induced current technique. This has allowed the recovery of smaller induced signals, even from films of low mechanical integrity following substrate removal. This technique has been applied to CdTdCdS solar cells deposited by the high vacuum evaporation technique. EBlC images of untreated and chloride treated devices suggest that this treatment produces higher efficiency regions near CdTe grain boundaries than In the grain interiors. This is explained by the collecting junction being closer to the CdStCdTe interface in the near boundary regions. compared with a more deeply buried junction within the grains. This conclusion is supported by beam voltage dependent EBIC measurements, which show unexpectedly efficient collection deep in the absorber layer. Comparison with previous work implies that this variation in junction position is due to higher doping near the grain boundaries.