German findings may explain high efficiency of perovskite PV

Scientists have found a clue for the remarkably high efficiency of perovskite solar cells. Researchers from Forschzungszentrum Jülich (FZJ) discovered that one of the main mechanisms causing energy loss is different in this material than in most semiconductors.

When a photon of sufficient energy hits a solar panel, an electron is dislodged and promoted to the higher-energy conduction band, leaving behind a hole in the valence band. The electron and the hole are pulled into different directions by an electric field inside the material, creating a flow of electricity. Unfortunately, more often than not, electrons and holes recombine before they find their way to an electrical contact. This typically occurs at defects of the crystal lattice.

“It had previously been assumed that recombination is predominantly triggered by defects that are energetically located in the middle between the valence and conduction bands. This is because these deep defects are similarly accessible to excited electrons and their counterparts, the holes,” says Thomas Kirchartz, who heads up a FZJ research group on organic and hybrid solar cells.