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  Sci. Lett. J. 2012, 1: 21  
  Research Article
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Influence of the CF4+O2 plasma treatment of ZnO:Al on a-Si p-i-n solar cell performance  
  J. D. Santosa, S. Fernándeza, A. Casadoa, J. L. Baldonedob, O. De Abrilc, C. Maffiottea, J. Cárabea, J. J. Gandíaa  
a CIEMAT, Av. Complutense, 22, 28040, Madrid, Spain
b Centro de Microscopía Electrónica “Luis Bru”. Ciudad Universitaria, 28040 Madrid, Spain
c ICMM-CSIC, Cantoblanco. 28049 Madrid, Spain

  The transparent conductive oxide (TCO) is commonly used as front electrode in p-i-n solar cells. Its surface state has an important impact on the amorphous silicon (a-Si:H) nucleation, and hence on the device efficiency. Specifically, the TCO surface morphology should be controlled to assure the growth of a dense enough a-Si:H structure. Otherwise, ohmic current paths might develop in the solar cell, causing an electrical loss increase. The application of a plasma treatment allows the elimination of possible imperfections on the TCO surface. Thus, the final device shows a higher shunt resistance, and consequently a better performance. This work addresses the problem of the shunting behaviour observed in our a-Si:H p-i-n devices deposited onto sputtered ZnO:Al (AZO). As a solution, a CF4+O2 plasma treatment was used to smoothen the AZO surface. For exposure times around five minutes, the elimination of surface defects led to a more compact a-Si:H structure, and a notable fill factor improvement was observed. Nevertheless, for long enough exposures, this dry-etching process caused an important deterioration of the AZO electrical characteristics. The effect of the CF4+O2 plasma treatment on the AZO bulk and surface properties was also studied.  
  a-Si:H; AZO; Solar cell; CF4+O2; Dry-etching; Shunt resistance  
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