Nondestructive silicon wafer recovery by a novel method of solvothermal swelling coupled with thermal decomposition

Abstract

• 86.11% of Si-wafers in commercial PV module can be reclaimed without damage. • The formation of gas release channels contributes to the nondestructive recovery. • PV backsheet removal avoids the fluorine-containing gas emission. • Solvothermal swelling strategy provides significant time and organic solvent savings. • The reclaimed silicon wafer meets the requirements of new PV module fabrication. End-of-life (EoL) photovoltaic (PV) waste is becoming a severe environmental issue worldwide. Developing technologies to reclaim nondestructive and reusable silicon wafers (Si-wafers) is the most appealing way to solve this problem, saving ~40% on PV module production costs, but it remains a great challenge. Herein, we develop a novel method of coupling solvothermal swelling with thermal decomposition (SSTD) for structure-intact Si-wafers recovery. Laboratory-scale studies reveal that undamaged Si-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. The reclaimed Si-wafers are comparable to the originals, with the following properties: interstitial oxygen, <6 × 10 17 atoms·cm −3 ; substitutional carbon, <5 × 10 17 atoms·cm −3 ; resistivity, 1.84 Ω·cm; and minority carrier lifetime, 3.92 μs.