Influence of the structural differences between end-of-life Al-BSF and PERC modules on the Al leaching separation behavior

Abstract

The booming global photovoltaic industry is bringing a large number of end-of-life photovoltaic (PV) modules. Achieving effective and green recovery of end-of-life PV modules is crucial to perform the energy and environmental sustainable development. The passivated emitter and rear cell（PERC) modules are the mainstream products in the current solar cell market, while the aluminum back surface field cell（BSF)modules were the mainstream products in the previous solar market. These two types of modules currently occupy the main share of the recycling market. There are several studies on the separation and recovery of valuable metals in the end-of-life PV modules. However, the influence of different cell processes and structures on the separation behavior of mainstream impurities in cells remains unclear. In this paper, the impacts of the structure of PERC and Al-BSF cells on the separation behavior of dominant Al impurity were studied. The structure and component difference between the PERC cells and Al-BSF cells was first clarified. The relationship between the loss rate of silicon wafer and the leaching rate of the aluminum back impurity was then studied. The results showed that the local contacts between the Al layer and Si wafers were primarily formed in PERC cells, in which the higher temperatures and longer leaching times were required to achieve the same Al leaching efficiency of Al-BSF cells. As for the Al-BSF modules, in order to better balance the Al separation and silicon loss rate during the alkaline leaching process, the reaction time should be set in the range of 7–10 min. The leaching rate of aluminum can reach 97.5% at 25 °C and 1 M NaOH for 10 min. After leaching, a layer of residual Si-O-Al alloy phase which is attached to the back surface of the two kinds of cell was observed. This study has a guiding significance for the green and efficient recovery of the silicon wafer in photovoltaic (PV) modules.