TITANIUM DIOXIDE AS ANTI-REFLECTIVE COATING FOR CRYSTALLINE SILICON SOLAR CELLS

摘要

We investigate the optimum thickness combination of an anti-reflection titanium dioxide film and asurface passivation silicon dioxide layer. Titanium dioxide is deposited in an Atmospheric Pressure Chemical VapourDeposition at 260°C and silicon dioxide is grown by a dry oxidation on a mono-crystalline silicon substrate.Measurements of unencapsulated samples show optimum results of around 10.5 % weighted reflectance(corresponding to the AM1.5G spectrum) for polished and 3.5 % for textured samples. When encapsulated,reflectance increases to 11 % for polished respectively 5.5 % for textured samples. These optima occur for titaniumdioxide thicknesses between 60 nm and 85 nm, and silicon dioxide thicknesses between 0 nm and 15 nm. Sufficientsurface passivation (emitter saturation current density ≤ 50 fA/cm~2) is achieved for silicon dioxide thicknessesgreater than 10 nm for <100> and 20 nm for <111> oriented surfaces. Relying on a simple solar cell model, theoptimum thickness combinations (silicon dioxide, titanium dioxide), regarding cell efficiency, are (15 nm, 50 nm) for<100> and (20 nm, 50 nm) for <111> oriented surfaces.Based on the experimental results a model has been developed, that allows to reliably predict reflectance for furtherexperiments. For 15 nm silicon dioxide, the calculated optimum titanium dioxide thickness shifts to 55-60 nm.