Experimental Determination of Atomic Scale Structure and Energy-Level Alignment of C₆₀ on CsPbBr₃(001)

The efficiency and stability of perovskite solar cells are largely determined by the interfaces between different functional layers in the device. Here, we investigate the atomic scale structural and electronic properties of C₆₀ on thin films of CsPbBr₃ on Au(001) by scanning tunneling microscopy and spectroscopy (STM/STS). By varying the PbBr₂ content of the film, we control the surface termination, switching between CsBr and PbBr₂, with each exhibiting distinct reconstructions. Investigating the self-assembly of C₆₀ in the submonolayer regime, we find that the molecule-substrate interaction is enhanced on the PbBr₂-terminated perovskite film. By STS, we determine the electronic energy-level alignment of the C₆₀ frontier orbitals, revealing that regardless of surface termination, a C₆₀ film functions as an electron transport layer in a device. However, different surface terminations induce a significant shift in the molecular energy levels by 0.4 eV, with implications for electron mobility and recombination losses in applications.