Halide perovskites have captivated the research community over the past decade mainly in the photovoltaic field as a new generation of absorber materials for high-efficiency and low-cost solar cells. Nowadays, the power conversion efficiency (PCE) is reaching 25.7% for single cells and 31.3% for Perovskite/Si tandem cells. Moreover, halide perovskites exhibit attractive potential for Lasers, LEDs, Photodetectors, Photocatalysis. Nevertheless, despite promising low manufacturing costs, short payback time and abundant material resources, the potential industrial use of halide perovskites is still be hampered by toxicity issues, device stability and upscaling. Researchers are also looking for alternative materials related to the substitution of Pb by Sn in standard halide perovskite structures, double perovskite structures, perovskite-like structures or even non-perovskite structures such as rudorfittes. 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. 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 . In view of the sophisticated chemical and physical properties of Sn-based perovskites, theoretical calculations based on density functional theory (DFT) may 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 team, we have evidenced the proportionality between work function shifts and surface dipoles, providing an additional microscopic insight into interfacial properties in lead-free heterostructures.