Characterisation of in-situ thermally evaporated CdS/CdTe thin film solar cells with Ni-P back contacts

CdS/CdTe thin film solar cells have been produced using the in-situ thermal evaporation of CdS followed by CdTe onto SnO2 coated glass substrates and a novel contact material, Ni-P, used to make contact to the p-CdTe. The specific contact resistivity of this contact to p-CdTe was found to be reduced to 0.08-0.01 Ohm . cm(2) for an optimum annealing temperature of 250 degrees C, the behaviour corresponding to a reduction in the percent of P in the Ni-P contact and an increase in photocurrent for illuminated CdS/CdTe/Ni-P solar cells. Photocapacitance data for such solar cells depended strongly on whether or not the devices had been given a CdCl2 heat treatment prior to contact formation, the heat treatment eliminating deep states within the CdTe. Shallow levels with depths of 0.10, 0.21 and 0.38 eV were observed for the untreated samples and shallow levels with depths of 0.04, 0.08, 0.15 and 0.21 eV for the CdCl2 treated samples.