Light Trapping in Isotextured Silicon Wafers

Abstract

We present an experimental investigation into light trapping within isotextured wafers. Measurements of reflectance and transmittance are performed on Si wafers both before and after the deposition of thin films on their surfaces. The wafers have a variety of surface morphologies that were created by varying the isotexture etch duration. We find that, unlike external reflectance, light trapping in isotextured wafers depends only weakly on the isotexture etch time (for practical etch durations). We also find that the light trapping induced by isotexture is similar to that induced by random pyramids. Moreover, we conclude that the spherical-cap model, which is extended to account for internal rays within the isotexture, can be applied to predict the transmittance and escape reflectance and, hence, the light trapping in isotextured wafers. By way of quantification, the model predicts the AM1.5g generation current to within ±1% and the reflectance and transmittance to within ±2% absolute for λ < 1100 nm (and to within ±4% for λ < 1200 nm for most samples). With an established light-trapping model, photovoltaic researchers can more accurately predict the behavior of isotextured solar cells for various antireflection coatings, encapsulants, and light sources.