Novel Low Cost Wet Chemical Cleaning Processes for Industrial Large Area n-Type Silicon Solar Cells with 22% Efficiency

We report on the development of industrial wet chemical cleaning processes for n-type passivated emitter, rear totally diffused (n-PERT) solar cells. PERT silicon solar cells with 22% efficiency have been manufactured comparing established silicon surface cleaning processes like sulfuric ozone mixture (SOM) with novel wet chemical processes based on DI water/ozone (DIW/O3) and industrial cleaning processes like diluted hydrochloric acid/hydrofluoric acid mixture (HCl/HF) as used in solar cell mass production. We have tested the different wet chemical cleaning methods on prominent metal impurities like Fe and Cu. These metals typically occur on the silicon wafer surface after alkaline processing like saw damage etch and texturing. It has been shown that the impurity removal efficiency of the different cleaning methods is varying strongly for different metals. This information is used for optimizing wet chemical cleaning processes in terms of bath lifetime and chemical consumption reduction. In this paper the results of the metal removal efficiency study is applied to a n-PERT solar cell process flow, but it could be applied on other high efficiency cells concepts like IBC or HIT as well.