Chemical bath deposition of photosensitive CdS and CdSe thin films and their conversion to n-type for solar cell applications

Methods for preparing good quality CdS and CdSe thin films of 0.1 - 0.7 micrometer thickness from solutions at 24 - 50 degree(s)C containing citratocadmium(II) ions and thiourea (for CdS) or N, N-dimethyl selenourea (for CdSe) are presented. The as prepared CdS thin films are photosensitive showing photo- to dark-conductivity ratio (S) of > 106 under AM-2 illumination. Annealing of these films at 400 - 450 degree(s)C for a few minutes converts them to n-type through partial conversion of the films to nonstoichiometric CdO. In the case of CdSe, such annealing improves the photosensitivity of the films from S equals 10 (as prepared) to greater than 107 (after annealing) under AM-2 illumination. Either film can be converted to n-type with dark conductivities of greater than 1 (Omega) -1 cm-1 and S equals 1 to 10 under AM-2 illumination using a post deposition treatment in dilute (0.01 - 0.05 M) HgCl2 solution followed by heating at 200 degree(s)C.