Formation of conductive CdO thin films on photoconductive CdS thin films for window layer applications in solar cells

We report the formation of a thin layer of CdO on chemically deposited US t hin films during air anneal at 370 degreesC to 500 degreesC for 5 min to 12 0 min. During a 5 min anneal, the sheet resistance of the US thin films dro ps from about 10(13) square /9 to 3.5 k square/square (370 degreesC) and 47 0 square/square (500 degreesC). X-ray diffraction studies showed that this is associated with the formation of a thin layer of CdO layer.. which occur s at temperatures above 370 degreesC. The US, which remains under the condu ctive CdO top layer, is photosensitive - with photo-to-dark current ratio o f 10(3) - 10(4). Essentially the air annealing converts the highly resistiv e and highly photosensitive intrinsic (i) CdS thin film into a (i)CdS-(n(+) )CdO layer. The technique offers prospects to convert the top part of a che mically deposited CdS thin film window layer of high photosensitivity, depo sited on an absorber layer, to a conductive layer. This is of interest in t hin film solar cell technology.