Analyzing Rapid-QE Data Using Rayflare

Johnson Wong1, Bernhard Mitchell1, Hannes Wagner-Mohnsen1, Phoebe Pearce2 1Wavelabs Solar Metrology Systems GmbH, Leipzig, --, Germany /2University of New South Wales, Sydney, --, Australia

1000 Topcon cells external quantum efficiency (EQE) curves are obtained at 27 representative LED wavelengths spanning from 350-1200nm.  These curves are fitted according to a representative optical model that incorporates the pyramidal textured silicon, antireflection coatings and rear heavily doped poly-Si layer of the typical Topcon solar cell, implemented using the open source software Rayflare.  Considering that it is infeasible to rigorously determine the multiple optical layers thickness and complex refractive indices simultaneously, the fitting procedure instead seeks plausible explanation of the layer parameters based on a priori knowledge of the manufacturing variance in each layer property.  This approach yields practical interpretation of measurement data that is conforming to the statistical distribution one expects in the manufacturing environment, reasonable accuracy in deriving manufacturing variance and their impact on device performance, and also allows for flexibility that more measurement data can be included in the fit to decrease the solution uncertainty.  For a subset of the samples, additional reflectance measurements are performed and included into the fitting procedure to assess the bias introduced by including/excluding the reflectance measurement data, as well as the improvement in uncertainty provided by them.