Cu(In,Ga)(Se,S)_2 Absorbers Formed by Rapid Thermal Processing of Elemental Precursors: Analysis of Thin Film Formation and Implementation of A Large Area Industrial Process

摘要

Large area Cu(In,Ga)(Se,S)_2 thin films (CIGSSe) for solar modules are processed by rapid thermal annealing of stacked elemental layers. A pilot line for 60 * 90 cm~2 absorbers and 30 * 30 cm~2 modules is now up and running. Modules with efficiencies at 12% are fabricated with excellent structural and electrical uniformity. For the optimization of electrical performance the selenization and sulfurization process is analyzed by x-ray fluorescence (XRFA), x-ray photo-electron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and current voltage (I-V) measurements. Sequentially processed CIGSSe films show characteristic depth distribution profiles of gallium and sulfur. Based upon our previously published model obtained by In-Situ XRD analysis the Ga profile can be explained by the strongly inhibited formation of binary gallium-selenides. The sulfur incorporation is investigated by comparing XRFA data and SIMS profiles of samples from different sulfurization recipes. A characteristic dependence of S on the Cu/(In+Ga) ratio is observed. Two different mechanisms for sulfur incorporation are proposed. It will be shown that the accumulation of sulfur towards the back is predominantly due to the incorporation into an intermediate molybdenum sulfo-selenide layer. Device characterization shows that the Ga and S profiles lead to a favorable double band gap grading structure.