Indium-Free Perovskite Solar Cells Enabled by Impermeable Tin-Oxide Electron Extraction Layers

Corrosive precursors used for the preparation of organic-inorganic hybrid perovskite photoactive layers prevent the application of ultrathin metal layers as semitransparent bottom electrodes in perovskite solar cells (PVSCs). This study introduces tin-oxide (SnO_x ) grown by atomic layer deposition (ALD), whose outstanding permeation barrier properties enable the design of an indium-tin-oxide (ITO)-free semitransparent bottom electrode (SnO_x /Ag or Cu/SnO_x ), in which the metal is efficiently protected against corrosion. Simultaneously, SnO_x functions as an electron extraction layer. We unravel the spontaneous formation of a PbI₂ interfacial layer between SnO_x and the CH₃ NH₃ PbI₃ perovskite. An interface dipole between SnO_x and this PbI₂ layer is found, which depends on the oxidant (water, ozone, or oxygen plasma) used for the ALD growth of SnO_x . An electron extraction barrier between perovskite and PbI₂ is identified, which is the lowest in devices based on SnO_x grown with ozone. The resulting PVSCs are hysteresis-free with a stable power conversion efficiency (PCE) of 15.3% and a remarkably high open circuit voltage of 1.17 V. The ITO-free analogues still achieve a high PCE of 11%.