Airbrush Coated PEDOT:PSS Back Contacts for Silicon Solar Cells

In this work, we demonstrate the use of an in-house built automated airbrush system to spray coat PEDOT:PSS layers on p-type silicon surfaces. We identify the effects of chemical additives on spraying reliability and show that the addition of a fluorosurfactant can provide a clog-free operation that is suitable for laboratory use. Next, we analyze the influence of hot plate temperature and nozzle height on the saturation current density (J0s) of PEDOT:PSS on mirror polished silicon. The silicon surface has either a wet chemically grown silicon oxide or the oxide stripped away by dipping into a hydrofluoric (HF) acid solution. For the samples with chemical oxides, J0s values below 30 fA/cm2 are achieved at an optimal hot plate temperature of ~180 °C. For HF-dipped samples, the J0s values are larger than 75 fA/cm2 and there is no clear dependency on plate temperature. Finally, we demonstrate the device performance using 2×2 cm2 silicon solar cells with double side pyramid texturing, phosphorus diffused front emitters and spray-coated PEDOT:PSS back contacts deposited on single side HF processed surfaces. We achieve the best cell performances at 100 °C and demonstrate a power conversion efficiency of 16.2%.