Single molecular precursor ink for AgBiS2 thin films: synthesis and characterization

Abstract

Recently, AgBiS₂ has been demonstrated to be a promising non-toxic, earth-abundant absorber material for solar energy application. In this work, a novel route to deposit AgBiS₂ thin films from single molecular precursor ink is presented. It is found that the amount of thiourea has a crucial impact on the formulation of a stable molecular ink. Understanding the coordination chemistry of the molecular precursor ink is important for getting better control over the thin film processing. With the assistance of Raman spectroscopy, possible complexation mechanisms and general coordination states within the molecular ink are studied. In addition, the influence of ink composition as well as the annealing temperature on the structure and morphology of resulting AgBiS₂ films is systematically investigated. It is found that the crystallinity and particle size increase with higher annealing temperature. The obtained AgBiS₂ thin films show a cubic structure with a preferred orientation in [111] direction. Optical and electrical measurements demonstrate that the obtained AgBiS₂ is an indirect band gap material, which features two transition mechanisms with an indirect band gap of around 0.87 eV and a direct one of around 1.21 eV. The high absorption coefficient, low Urbach energy and fast transient photoconductivity confirm its potential as an absorber for photovoltaic applications.