Accurate determination of the IQE of screen printed silicon solar cells by accounting for the finite reflectance of metal contacts

The internal quantum efficiency (IQE) of a solar cell follows from the external quantum efficiency (EQE) and reflectance data of the front side. Most of the silicon solar cells currently produced feature metallised areas on the front. To account for the finite reflection of the metal grid, the reflection of the non-metallised area has to be extracted from the reflection data. Our results show that neglecting the finite reflection of the front metallisation results in a misinterpretation of the IQE by up to 9 % (relative). We show that the impact of the metallisation on the front reflectance scales linearly with the surface ratio of the metallisation and present a method to extract the reflectance of non-metallised areas from large-area reflectance measurements of screen printed solar cells. Our approach uses an algorithm to automatically determine the metallised surface area by means of microscope images and reference measurements of fully metallised samples to calculate the required reflectance data. This way the accuracy of the IQE is significantly improved.