Fabrication of improved and stable thin film CdS:Cu2S solar cells by inhibiting vertical junction formation

A new technique to eliminate detrimental affects associated with narrow vertical junctions along CdS grain boundaries in wet processed CdS:Cu2S solar cells by manipulating the ion exchange kinetics through a negative DC potential at CdS is described. AES depth profiles indicate a build-up of Cd++ at the interface. Analysis of dark I-V characteristics at temperatures between -120 and +150°C show exclusion of tunneling mode of current transport. Saturation current density and the reverse leakage currents reduce by two orders of magnitude implying that both recombination and shorting centres associated with vertical junctions are reduced. A significant feature of the technique is improvement of Voc to .558 Volts for texturised cells. Improved spectral response of such cells show a stable chalcocite phase even after air heating and carrier generation near CdS. Isochronal annealing of junctions conclude that cells processed by the new technique are quite stable.