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 CH₃NH₃PbI₃ 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%.

Corrosive precursors used to prepare organo-metal-halide perovskite photoactive layers usually prevent the application of ultrathin metal layers in semitransparent bottom electrodes. Tin-oxide/metal/tin-oxide electrode is introduced, where the ultrathin metal layer is shielded by impermeable tin-oxide (SnO_x) grown by atomic layer deposition. The SnO_x concomitantly functions as an electron extraction layer that affords a high open circuit voltage of 1.17 V.

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