Top-Cell Ohmic Shunt Imaging in 2-Terminal Tandem Solar Cells by Differential Electroluminescence

Perovskite/silicon tandem photovoltaic cells promise higher energy conversion efficiencies than silicon single junctions for reasonable additional production cost. However, they are more complex, due to the increased number of layers and to the perovskite material features regarding kinetic, stability, and surface homogeneity. Although measuring each subcell independently from each other is still a challenge, this work introduces a novel quantified electroluminescence (EL) imaging method of the top-cell ohmic shunt, a major issue in perovskite stacks. Device modeling, validated by experiments, led to ohmic shunt 2D resolution from differential EL measurements around 0.7 V, without optical filtering or spectral resolution. The shunt resistance maps of more than 60 cells were characterized, and the shunt quantification from these maps was consistent with electrical measurements. These maps provide relevant clues regarding ohmic defect origin by showing their strength, shape, and location. Applications range from lab-scale performance improvement and aging monitoring to manufacturing control including encapsulation.