Tandem solar cells are effectively a stack of different solar cells on top of each other. Tandem solar cells can either be individual cells or connected in series. The most common arrangement for tandem cells is to grow them monolithically so that all the cells are grown as layers on the substrate and tunnel junctions connect the individual cells.Thus it becomes optimised to each section of the solar spectrum and capture more energy from the sun. Tandem solar cell is a type of multi-junction cell.