Non-thermal atmospheric pressure plasma etching of F:SnO2 for thin film photovoltaics

Thin film based photovoltaic systems offer significant advantage over wafer based technologies enabling the use of low cost, large area substrates such as glass, greatly facilitating the construction and integration of large modules. The viability of such systems has advanced in recent years, with researchers striving to optimise performance through the development of materials and cell design. One way to improve efficiency is to texture the interface between the TCO and the absorber layer to maximise scattering over the appropriate wavelength range, with nanometre scale features such as pyramids being reported as giving high scatter. These textures may be achieved by advanced growth processes, such as CVD, post growth etching or a combination of both. In this work, textured F:SnO2 films produced by APCVD were favourably modified using a remote, non thermal, atmospheric plasma to activate a selective dry etch process resulting in significantly enhanced topography. Uniform treatment of the samples was achieved by translation of the samples below the plasma head. Advantages of this approach, compared to competitive technologies such as wet chemical processes, are the relatively low power consumption and ease of scalability and retroprocess integration. The modified structures were studied using AFM, SEM and EDAX, with the observed topography controlled by process variables. Optical properties were assessed along with Hall measurements.