Modification of light scattering properties of boron doped zinc oxide grown by Low Pressure Chemical Vapour Deposition using wet chemical etching

The best light scattering properties for ZnO:B films grown by Low Pressure Chemical Vapor Deposition (LPCVD) require low doping in the precursors and films. Such films must be thicker than 2 μm to achieve sheet resistances ≤ 20 Ω/sq, suitable for thin film silicon solar cells. In this study, ZnO:B films, grown by LPCVD with different doping levels, were etched using several solutions so as to modify their surface morphology in a quick and simple way. The haze ratio, at 800 nm, of the films increased from values below 10 % to about 20 % after etching. Observation of the SEM micrographs confirmed that the film surface had been modified by the etching process. Highly doped films could be etched to achieve a high haze while keeping the sheet resistance below 15 Ω/sq. Tandem junctions consisting of amorphous silicon p-i-n and micro-crystalline silicon p-i-n solar cells grown on etched highly doped ZnO:B films exhibited higher open circuit voltage than those on a natively textured lower doped films. Further optimization of both the etching process and the starting ZnO:B material is expected to lead to higher solar cell efficiency. These results show that the optimum thickness of ZnO:B front contacts in thin film silicon can be reduced, potentially cutting production time and material costs.