Metal-organic perovskite layers for solar cells are often fabricated using the spin-coating technique on compact substrates. These perovskite layers generally exhibit holes, yet attain astonishingly high levels of efficiency. The reason that these holes do not cause significant short circuits between the front and back contact has now been discovered by a HZB team headed by Dr.-Ing. Marcus Baer in cooperation with the group headed by Professor Henry Snaith (Oxford University) at BESSY II.