Environmentally friendly approaches for recycling of CIGS solar cells
Doktorsavhandling, 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.

Silver

alkaline leaching

acid leaching

ITO recovery

CIGS recycling

ultrasonic-leaching

indium

molybdenum

Lecture hall KC, Kemivägen 4, Gothenburg, for the Degree of Doctor of Philosophy in Chemistry at Chalmers University of Technology
Opponent: Prof. Dr. Ragnhild Elizabeth Aune, NTNU (Norwegian University of Science and Technology), Norway

Författare

Ioanna Teknetzi

Kärnkemi och industriell materialåtervinning

In 2022, solar energy produced 4.5 % of the global electricity, by usings photovoltaic (PV) systems. The expected surge in PV deployment is going to be accompanied by considerable amounts of waste, produced in all the stages of the life of a PV, from its manufacturing until the end of its life. As PV can contain valuable and toxic materials, proper treatment of this waste should take place. Unfortunately, today recycling of PV waste is still under development.

The particular work explores the recycling of metals from a specific PV technology, based on a thin-film of Copper Indium Gallium diSelenide (CIGS). As there are very few methods proposed currently for its recycling and these tend to consume high amounts of chemicals and energy, there is a need for developing new processes, which will be efficient, result in high purity recovered materials, so that they can be reused again, and be more environmentally friendly. This work developed a complete separation process for all the valuable materials found in a CIGS solar cell, the most important component of a PV system, with a special focus on the valuable silver and indium. The process comprises three dissolution steps, each of them performed under different conditions. A very small amount of chemicals is used in each step and high temperatures are avoided. The valuable materials are liberated from the solar cell in the form of solids, by first dissolving layers deposited underneath them. The result is a complete separation of all the valuable materials of the solar cell into separate fractions of high purity, which can be purified even further easily. Experiments on the dissolution of the valuable metals from CIGS solar cells also proved that milder conditions than what is proposed in the literature can still be efficient. The solutions used for the dissolution can also be enriched in metals by being reused in many cycles, reducing the cost for chemicals and facilitating further separation and purification of the metals. In total, this work demonstrates that highly efficient and environmentally friendly recycling of CIGS solar cells is achievable and the developed methods are simple to implement.

Ämneskategorier (SSIF 2025)

Materialkemi

Separationsprocesser

Oorganisk kemi

Drivkrafter

Hållbar utveckling

Innovation och entreprenörskap

Infrastruktur

Chalmers materialanalyslaboratorium

ISBN

978-91-8103-196-6

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5654

Utgivare

Chalmers

Lecture hall KC, Kemivägen 4, Gothenburg, for the Degree of Doctor of Philosophy in Chemistry at Chalmers University of Technology

Opponent: Prof. Dr. Ragnhild Elizabeth Aune, NTNU (Norwegian University of Science and Technology), Norway

Mer information

Senast uppdaterat

2025-03-21