Continuous-wave laser annealing of metallic layers for CuInSe₂ solar cell applications: effect of preheating treatment on grain growth

Abstract

Ultra-fast thermal annealing of semiconductor materials using a laser can be revolutionary for short processing times and low manufacturing costs. Here we investigate Cu-In-Se thin films as precursors for CuInSe 2 semiconductor absorber layers via laser annealing. The reaction mechanism of laser annealed metal stacks is revealed by measuring ex situ X-ray diffractograms, Raman spectra and composition. It is shown that the formation of CuInSe 2 occurs via the formation of Cu x Se/In x Se y binary phases as in conventional annealing routes, despite the entirely different annealing time scale. Prealloying the Cu and In metals prior to laser annealing significantly enhances the selenisation reaction rate. Laser annealing for six seconds approaches a near phase-pure material, which exhibits similar crystalline quality to the reference material annealed for ninety minutes in a tube furnace. The estimated quasi Fermi level splitting deficit for the laser annealed material is only 60 meV lower than the reference sample, which implies a high optoelectronic quality. † Electronic supplementary information (ESI) available: Compositional mapping on cross section images, digital photograph of a laser-annealed sample, description of laser scan movement. See Fig. 3 SEM images of the annealed samples. Top-view images of LA samples annealed for 2, 4, and 6 s, with and without the pre-alloying step. The top view and cross sectional images of the reference material (thick oven) are also included for comparison.This journal is