CHARACTERIZATION OF ETCHING PROCEDURE IN PREPARATION OF CDTE SOLAR-CELLS

An etching procedure for forming a low resistance contact to polycryst alline CdTe thin films in CdS/CdTe solar cells was studied, The etchin g solution used was a mixture of HNO3, H3PO4 and H2O. X-ray diffractio n (XRD), secondary ion mass spectrometry (SIMS) and electric measureme nts revealed that the etching results in a formation of crystalline te llurium on the film surface, thereby increasing substantially the cond uctivity of the surface layer. The total process was found to consist of three steps: (i) immediately after an immersion into the etching so lution there was a certain induction period with no discernible change s, (ii) a subsequent reaction step during which poorly crystallized el emental tellurium was formed, gaseous byproducts liberated and the sur face changed its colour, and (iii) after taking out of the etching sol ution the tellurium crystallized causing a strong decrease in the shee t resistance. In situ XRD and electric measurements were carried out t o follow the third step. The chemical aspects of the three steps as we ll as their contributions to the reproducibility and control of the ov erall etching procedure have been considered.