To cope with the toxicity of Pb-based perovskites and achieve smaller electronic band gaps, replacing Pb with Sn has gained growing attention recently 1,2. Importantly, the low-bandgap Pb-Sn alloyed perovskite allows the building of all-perovskite tandem solar cells that shall overcome the performances of single-junction perovskite cells 3,4. In fact, of all possible means to improve perovskite film quality and suppress nonradiative recombination in optoelectronic devices for a high photo conversion efficiency purpose, the surface and interface functionalizations after the assembly with charge transport layer (CTL) are one of the most critical parameters 5,6. In view of the sophisticated chemical and physical properties of Sn-based perovskites, theoretical calculations based on density functional theory (DFT) provide a useful insight into the interplay between absorbers and CTLs. Here, FASnI3 is chosen as a benchmark material. We thoroughly investigate the influence of its surface termination on structural and electronic properties when interfacing with organic C60 (100) and inorganic SnO2 (100) and (110), including the intermediate work function calculations on the free-standing slabs. Based on the theoretical methology developed in our team7, we have evidenced the proportionality between work function shifts and surface dipoles, making the optimization of interfacial charge transport possible by surface dipole tuning. Our findings on the charge transport properties of the two targeted CTLs, contribute to analyzepromising alternatives as CTLs for Pb-free perovskites thanks tosurface and interface engineering.