| Summary: | BackgroundAll-inorganic perovskite solar cells have been extensively studied for their phase and thermal stability. In perovskite solar cells, the interface energy level arrangement between the hole transport layer (HTL) and the perovskite layer plays a decisive role in the performance of the device. Suitable interfacial energy level alignment is essential to facilitate the injection of photogenerated holes from perovskite into the HTL simultaneously effectively block electron transport efficiently, thus suppressing the recombination of holes with electrons.PurposeThis study aims to precisely determine the interfacial energy level alignment between CsPbI2Br and Spiro-OMeTAD experimentally.MethodsFirst of all, the Spiro-OMeTAD was deposited on CsPbI2Br film, then the interfacial electronic structure between CsPbI2Br and Spiro-OMeTAD was investigated by in situ X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. Finally, the fabricated CsPbI2Br film was characterized by synchrotron-based grazing incidence X-ray diffraction (GIXRD) and scanning electron microscope (SEM).ResultsExperimental results show that there is no detectable interaction observed at the Spiro-OMeTAD/CsPbI2Br interface where electrons accumulate due to the formed interfacial state. An interfacial dipole of 0.18 eV is formed at the interface with 0.13 eV and 0.27 eV upward energy band bending at the CsPbI2Br substrate side and the Spiro-OMeTAD side, respectively. The hole injection barrier at the interface as indicated by the gap between the CsPbI2Br valence band maximum (VBM) and the Spiro-OMeTAD highest occupied molecular orbital (HOMO) is determined to be 0.23 eV, which favours the hole injection and extraction. Meanwhile, the gap between the CsPbI2Br conduction band minimum (CBM) to the Spiro-OMeTAD lowest unoccupied molecular orbital (LUMO) known as the electron-blocking barrier is up to 1.25 eV, effectively blocking the electron transfer from CsPbI2Br to Spiro-OMeTAD with the interfacial recombination efficiently suppressed.ConclusionsIt is concluded that Spiro-OMeTAD is an excellent HTL material in CsPbI2Br-based all-inorganic perovskite solar cells. The present work also provides meaningful guidance for the tunning interfacial electronic structure between perovskite and HTLs for high-performance CsPbI2Br solar cells.
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