Influence of CdCl2 treatment of CdS on the properties of electrodeposited CdS/CdTe thin film solar cells

The effects of cadmium chloride treatment on the thin (0.2 μm) CdS layer in electrodeposited CdS/CdTe cells have been studied by comparing cell characteristics of sixteen cells with that treatment with those of sixteen cells without that treatment immediately after fabrication and after 180 days. Cells with the treated CdS layers (type A) had higher and more stable U_oc values e.g. 753±5 mV (t=0), 742±7 mV (t=180) compared with the untreated cells (type B) of 712±18 mV (t=0), 660±15 mV (t=180). CdCl₂ improved the CdS crystallinity as observed from electron microscopy and inferred from optical measurements. Current-voltage-temperature measurements showed that the current transport for both sets of cells was controlled by both tunnelling and interface recombination but type A cells displayed less tunnelling. The reverse saturation current, J₀ , for type A cells was 2.0±0.1 nA cm^-2 (t=0 and 180) compared with type B cells for which J₀ was 16 nA cm^-2 (t=0) and 25 nA cm^-2 (t=180). The type A cells displayed little variation of capacitance at 10 kHz with reverse bias indicating the presence of an intrinsic or low doped depletion layer present at the CdS/CdTe interface. Surface analytic studies suggested the presence of a CdS_xTe_1-x compound