Non‐vacuum deposition of Cu(In,Ga)Se2 absorber layers from binder free, alcohol solutions

ABSTRACT Non‐vacuum methods for Cu(In,Ga)Se 2 (CIGS) absorber deposition have gained wide interest because of their inherent cost and energy saving potential. Here, a solution‐based processing route for CIGS absorber layers is presented that employs binder‐free solutions of metal salts in non‐toxic, alcohol solvents. Despite the low‐boiling‐point nature of the employed solvents, a residual carbon‐rich layer is observed between the CIGS and metal back contact. Based on comprehensive investigations by scanning electron microscopy, energy‐/wavelength dispersive X‐ray spectroscopy, X‐ray fluorescence, X‐ray diffraction, thermogravimetric analysis, differential thermal analysis, and extended X‐ray absorption fine structure spectroscopy, a formation reaction mechanism through intermediate metal–organic complexes is proposed. In this route, the CIGS layer is formed in selenium atmosphere via a gradual decomposition of the carbon‐rich layer comprising carboxylic chelate complexes of metals. A compositional gradient occurs in the CIGS absorber, whereas a significant amount of metals remains in the carbon‐rich layer. The incorporation of Ga into CIGS is affected by the initial salt concentration and the selenization temperature. Fabricated solar cells exhibit active area efficiencies of up to 7.7% on 0.3 cm 2 area without anti‐reflection coating, which is among the highest reported efficiencies for solar cells from a solution process with non‐explosive gases or solvents. Copyright © 2012 John Wiley & Sons, Ltd.