Selective recovery of the CIGS and Mo layers from thin film solar cells

The Cupper Indium Gallium diSelenide (CIGS) Photovoltaic (PV) technology is well established in the market and considered as a good candidate for incorporation in other, more recently developed and complex PV technologies (e.g. tandem). Despite its popularity, little research has been done on the recycling of its materials, which contain valuable, critical and toxic elements. In this paper, the possibility of recovering in solid form the valuable CIGS material from CIGS solar cells, through first selectively leaching the Mo layer deposited underneath and subsequently liberating the unsupported CIGS by mechanical means, was explored. Different NaOH concentrations, process temperatures and means of mechanical liberation of the unsupported CIGS were investigated. The results showed that although a range of the tested NaOH concentrations could efficiently dissolve the Mo even at ambient temperature, for 0.1-0.5 M NaOH, some of the CIGS reacted with the NaOH and the compositional elements of the former ended up scattered in various phases. This was not the case when using a dilute NaOH solution of pH = 11 at 50 °C with an automatic titration system for keeping the pH constant. More specifically, after the application of these conditions for 8 h and a subsequent mechanical brushing of the substrate, the composition and crystalline structure of the recovered CIGS had remained practically unaffected, compared with the untreated material. Complete recovery of the CIGS was then achieved, with a purity of about 95 wt%. Simultaneously, 82 wt% of the Mo was recovered in the leachate. • 95 wt% pure solid CIGS, recovered after alkaline leaching and brushing of solar cells. • Recovery of solid CIGS via alkaline leaching of the Mo-containing layers underneath. • A range of NaOH concentrations can leach completely the Mo. • Leaching at pH = 11 at 50 °C for 8h offers efficient and selective recycling.