When light of specific frequency hits a semiconductor crystal, it is absorbed and produces excitation, a state of higher energy. In solar cells, this energy is converted into electricity. In two-dimensional crystals, which consist of only a few atomic layers, so called “excitons” are the protagonists of these processes. These excitations consist of one particle of positive charge and one of negative charge. Yet, two-dimensional crystals host a multiplicity of excitons, making it hard to distinguish the kinds of excitons in specific situations. Researchers of TU Dresden, in collaboration with an international team, have now identified the nature of interlayer excitons in two-dimensional crystals. Their findings were published in the journal Nature Physics.