Enhanced optical performance of APCVD zinc oxide via post growth plasma treatment at atmospheric pressure

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Hodgkinson, JL ; Yates, HM ; Sheel, DW

The use of atmospheric pressure (AP) CVD to produce\ud highly developed Transparent Conducting oxides (TCO)\ud for thin film photovoltaic systems has significant potential\ud to reduce manufacturing costs and increase the product\ud scope via in-line processing compared to off-line, low\ud pressure techniques. A further advantage of APCVD is\ud the ability control surface morphology via growth parameters, a key factor in controlling the distribution of\ud scattered light at the TCO/absorber interface. The nanoscale\ud features may be further optimised via post growth etching, for example, to round sharp vertices or induce or\ud exaggerate texture in a film material that is intrinsically\ud smooth. This is normally achieved via low pressure\ud plasma treatments or wet chemical processes, hence the\ud presented novel AP plasma approach here offers reduced\ud capital costs combined with ease of scalability and process\ud integration. In this work we describe the multi-scale\ud manipulation of an APCVD grown ZnO via surface morphological\ud modification, achieved by the application of\ud an atmospheric pressure plasma etch system. The modified\ud surfaces are evaluated for optical and morphological\ud properties. Initial research has shown that under the correct plasma etch conditions, optical haze can be increased by as much as 20%, with the crucial additional ability to also tailor the film surface features. The use of audio frequency and sub-microsecond pulsed plasmas for etching are compared in terms of activity and control.
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