Environmentally friendly approaches for recycling of CIGS solar cells

Doctoral thesis, 2025

The expected huge increase in photovoltaics (PV) deployment is going to be accompanied by a considerable volume of PV waste. Recycling of this waste is still at a primitive stage though. Among the current PV types, the Copper Indium Gallium diSelenide (CIGS) thin-film technology can achieve high energy conversion efficiencies, while consuming small amounts of materials. However, the presence of critical, precious and toxic elements in this PV technology demands its waste to receive proper treatment, in order to address resource scarcity, safety and economic issues. The existing limited literature on waste recycling of two of the most important elements present in a CIGS solar cell, namely indium (In) and silver (Ag), suggests their separation from the waste mainly through acid leaching, using high chemicals concentrations and often high temperatures. However, such conditions are not environmentally friendly and can also be costly for the industry. Another challenge in their recycling is the demand for highly selective recovery processes, since only highly pure recovered materials can replace virgin materials. In this work, these issues are addressed by exploring alternative methods for efficient and selective recovery of materials from CIGS solar cells, characterized by low environmental impact, in terms of chemicals and energy consumption. For this purpose, different conditions for Ag and In recovery were tested and two different recovery processes were developed: first, a high efficiency acid leaching of Ag and In and, later, a selective recovery of solid Ag and In-compounds. The prior method achieved a complete leaching of Ag and an about 85 wt% leaching of In in 24 h using 2 M HNO3. The same leachate proved to be able to be used for at least 10 leaching cycles, without losing its leaching efficiency per cycle for these two metals. However, a considerable amount of many other elements present in the solar cell leached as well. In the latter recycling approach, complete dissolution of Zn and liberation of Indium Tin oxide (ITO) particles were achieved in a first step, using only 0.1 M HNO3 and low ultrasonic (US) power. In a second step, the Ag grid was recovered, using 0.1 M HNO3 and high US power. The remaining material was then leached with a solution of pH=11 at 50 ℃, with the aim to selectively dissolve Mo and subsequently liberate the CIGS material on top of it. As a result, separate fractions of solid Ag, ITO and CIGS, dissolved Mo (with or without W and Ti) and Zn and the solid stainless-steel substrate were recovered. The developed methods are simple and can be attractive for the recycling industry.