The fast-growing development of environmentally friendly energy generation methods have brought about the explosion of photovoltaic (PV) modules in recent decades. To date, the estimated cumulative installed capacity of PV modules has dramatically increased to 715 GW globally and 259 GW in China. In this regard, the limited lifetime (~25 years) of PV modules will lead to a significant amount of end-of-life PV modules. Currently, improper landfilling of PV module wastes is intolerable due to the leaching of hazardous heavy metals (e.g., lead and cadmium). Instead, collection and recycling is becoming the general trend.

Recently, a research group led by Prof. WANG Yin from the Institute of Urban Environment (IUE) of Chinese Academy of Sciences (CAS), proposed a novel method of solvothermal swelling coupled with thermal decomposition for nondestructive silicon wafer recovery from crystalline silicon base PV module. This study has been published in Chemical Engineering Journal.

The research results show that undamaged silicon wafers can be easily obtained by conducting a solvothermal swelling process in advance to build channels for the quick, horizontal release of ethylene-vinyl acetate (EVA) thermal decomposition gas. Using scaling-up equipment, 86.11% of Si-wafers in commercial PV module are reclaimed without any damage, nearly 10-fold higher than that of thermal decomposition alone (9.26%). Moreover, PV backsheet can be depolymerized with specially designed solvents (toluene-ethanol), greatly facilitating swelling by exposing EVA directly to toluene vapor and reducing the emission of fluorine-containing gas pollutants. Properties of the reclaimed silicon wafers, including interstitial oxygen, substitutional carbon, resistivity, and minority carrier lifetime were comparable to the originals.

This work was supported by the “Strategic Priority Research Program (A)” of the Chinese Academy of Sciences, FJIRSM&IUE Joint Research Fund, the Industry Leading Key Projects of Fujian Province and the Science and Technology Program of Xiamen.

Schematic diagram of the (a) crystalline silicon base PV module structure and (b) silicon wafer nondestructive recovery system with solvothermal swelling-thermal decomposition technology.