Metal halide perovskites (MHPs) exploitation represents the next big frontier in photovoltaic technology with power conversion efficiencies above 26 %. However, two main drawbacks limit the potential application and commercialization of the technology: toxicity, due to the presence of lead, and instability under moisture, light and temperature, among other factors.  Currently, research efforts are dedicated to the synthesis of novel Pb-free MHPs with elements such as tin (Sn), germanium (Ge), bismuth (Bi), Titanium (Ti) or antimony (Sb) as substitutes for lead (Pb). Although the tin-based perovskite solar cell is the most promising candidate, other promising PSCs with elements such as Bi (with current efficiencies around 5 %) are being highly studied. Among the different approaches employed to boost the stability of halide perovskite solar cells, A-site substitution using organic ligands, has been the centre of research worldwide. In lead perovskite solar cells, A-site substitution with various organic and inorganic materials has been commonly explored to control the optoelectronic properties and consequently improve device performance. Cations such as methylammonium (MA+), formamidinium (FA+), phenethylammonium (PEA+), ethane- 1,2-diammonium (EDA+), and guanidinium (GA+) ions have shown positive outcomes when used at optimized stoichiometries in perovskite solar cell devices. Recently, a novel A-site cation, dimethylammonium (DMA+) cation, has been introduced in Pb-containing perovskite solar cells, which enhanced the photovoltaic performance and device stability. DMA can act as an A-site cation to incorporate with CsPbI3, creating a hybrid perovskite of CsxDMA1-xPbI3, which is more stable in ambient conditions than pure CsPbI3. This enhancement in stability is also observed when partial substitution of the large dimethylammonium (DMA) cation at the A site of FAxCs1–xPbIyBr3–y perovskites, results in a bandgap increase and it is accompanied by an expansion of the crystal lattice. The solar cells resulted extremely stable, retaining 96% of their original efficiency over 2200 h at 85 °C in the dark and 92% of their original efficiency after operation at 60 °C for 500 h. It is particularly noteworthy the high stability and hydrophobicity of DMASnX3 and PEA2SnX4, the Pb-free MHP do not dissolve in water, but it rather remains dispersed in solution, maintaining unchanged the crystal structure and the optical properties. The latter makes this perovskite an interesting candidate as photocatalyst. In this presentation, I will show our most recent results on the synthesis of Pb-based and Pb-free halide perovskites and their application as solar cells and potential photo(electro)catalyst. The materials were fabricated as heterojunctions with MXene thin films.