Achieving air, heat and light stabilities in the perovskite solar cells (PSCs) have long been sought after due to their susceptibility to the performance loss especially upon exposure to the humid and high temperature environment and also the presence of the UV light. In this research, the improvement in the performance stabilities of the tin-lead (SnPb) PSCs was studied via doping and interlayer engineering. Doping technique has been used widely in order to improve the performance of the PSCs because doping materials are able to rectify certain defects and passivate the perovskite surface to produce high efficiency PSCs. The interlayer between the stacks of the inverted p-i-n single junction SnPb PSCs was modified between control devices and the target devices, i.e. the use of different hole and electron transport layers, and/or, the incorporation of inorganic base carrier extraction layers. Various research have demonstrated the positive impact on the performance of the PSCs via interlayer engineering due to the reduced interfacial recombination and also good energy alignment for effective carrier extractions. These effects which also brought the improvement in terms of air, heat and light stabilities have been demonstrated in various studies involving lead (Pb) based PSCs. However, there is a knowledge gap for SnPb based perovskite solar cells, more research is required in order to produce SnPb PSCs with similar performance to their Pb PSCs counterpart. This adverse performance gap occurred mostly due to the presence of the vulnerable tin (Sn) component in the SnPb PSCs. Sn component in the SnPb based perovskite films makes the perovskite films easily oxidized, especially in high humidity and high temperature ambient. The chemical and the physical structure of the SnPb perovskite films will be altered upon oxidation which in turn compromising the PSCs performance. In this study, we introduced metallic (Rb, K, etc.) halide doping materials in the SnPb perovskite films in the SnPb perovskite materials for performance enhancement. The thermal stability of the PSCs was investigated by analyzing their performance using solar simulator by subjecting the PSCs to the temperature over 85 °C for 150 hours in nitrogen atmosphere. From series of experiments, we managed to achieve SnPb based PSCs with the highest efficiency of more than 21% and demonstrated high photo and thermal stability when metallic halide dopants were incorporated. The SnPb PSCs which was stored in the nitrogen filled air are able to retain about 99% of their efficiencies after 1 month of storage. In term of thermal stability, the PSCs are able to retain more than 75% of their initial efficiencies after subjected to the temperature over 85 °C for 150 hours in nitrogen atmosphere. We will elucidate the successful treatment of the doping and interlayer engineering by studying the morphological, structural and elemental of the thin films before and after exposure to thermal heating via SEM, XRD and XPS. We demonstrated the effects of doping and interlayer engineering via impedance spectroscopy technique by extracting the electronic parameters in the SnPb PSCs such as the series and recombination resistances, and also the capacitance of the investigated devices. Indeed, the champion device with the incorporation of doping element and modified interfacial layer exhibited lowest series resistance and highest recombination resistance. The ionic diffusion was mitigated in the champion device as we analysed the capacitance at different operating frequencies. We conclude this research by proving the performance of the SnPb based PSCs will be enhanced by integrating metallic halide dopant and modified interfacial layers; rendering them more stable thermally and beneficial for long term application.