Recovery of silver from end-of-life photovoltaic cells via mild glucose reduction to produce high-purity ultrafine silver powder for conductive silver paste

Abstract

Recovering silver from end-of-life (EoL) photovoltaic (PV) cells is of great significance for closing the resource loop in the photovoltaic industry. Currently, the conventional silver recovery processes mainly include acid leaching, chlorination precipitation, ammonia dissolution and liquid-phase reduction. However, the recovered silver powder cannot be directly used for silver paste preparation and requires complicated post-treatment procedures. Adjusting the reduction process to obtain ultrafine silver powder directly applicable to silver paste can effectively shorten the application process of silver and reduce costs. In the current study, glucose is employed as a mild reducing agent to regulate the reduction rate and the morphology of obtained silver powder. Unlike direct strong reductants, this mild reduction avoids burst nucleation and enables morphology control. Temperature and solution pH value are the two most critical factors affecting the efficiency of the reduction reaction, which promote the ring-opening and isomerization processes, respectively. The recovered silver powder has a purity of 99.58% with relatively narrow particle size distribution (480 ± 101 nm) and good dispersibility. The powder can be directly used for high-temperature conductive silver paste without requiring secondary processing. The sheet resistance of the silver paste after sintering ranges from 3.0 to 4.8 mΩ/sq. In terms of numerical values, it is comparable to the national standard for solar cell silver pastes (≤5.0 mΩ/sq). This work develops a closed loop of recovery-regeneration-application for photovoltaic silver resources and provides a short-process, low-cost approach.