However, until now, it has been known that for all their gains in efficiency, organometal halide hybrid perovskites have faced stability challenges due to presence of defects, disorder and heterogeneity on photoexcited carrier dynamics. Mixed-cation perovskites solar cells have consistently outperformed their single-cation counterparts in both efficiency and stability cases. The first perovskites device to exceed 20% power conversion efficiency was fabricated with a mixture of methylammonium and formamidinium and improved stability. Recent reports have shown promising results with the introduction of cesium mixtures, enabling high efficiencies with improved photo-, moisture and thermal stability. McGehee 12 reported exceptional stability for new perovskites recipes that replace an organic component called methylammonium with formamidinium or the element cesium. The combination of the more stable perovskite and the protection provided by the ITO layer allowed the cells to operate for more than 1000 hours in air and 40% humidity without significant degradation. When encapsulated to protect them from moisture, these cells showed no sign of degradation for six weeks, even when exposed to temperatures of 85°C and a relative humidity of 85% for 1000 hours, a standard test of durability. -Panels that pass it usually will not fail due to heat and humidity over 25 years outside,‖ McGehee says. The increased moisture and thermal stability are especially important for various reasons including deposition of metal oxide contacts through atomic layer deposition or chemical vapour deposition that may require elevated temperatures or water as a counter reagent. With all these concerns, it is reasonable to find an alternative perovskites material that can improve the photo-, moisture and thermal stability issues of methylammonium based organolead halide hybrid perovskites solar cells. This is due to the reasons that methylammonium cation is weakly stable towards moisture and thermal treatments and it is more preferable to find materials with reasonable stability and relatively high efficiency for practical applications. The materials community is currently witnessing a fundamental change in the way novel materials are designed and discovered. A steady increase in computational power, accompanied by developments in quantum theory and algorithmic breakthroughs that allow for efficient yet accurate quantum mechanical computations, opens the door to computing properties of a wide range of materials that once seemed prohibitively expensive. As a result, explorations of the vast chemical space are increasingly being pursued and have significantly aided our intuition and knowledge-base of material properties. In our previous work we synthesized bulk crystals of MAPbI 3 . We, herein, investigated crystal structure, electronic and optical properties of CuPbI 3 , CuPbBr 3 , CuPbCl 3 and AgPbI 3 fully inorganic new perovskites for the first time, with the purpose for more stable and optimal light absorption compared to the methylammonium based organometal halide perovskites. First Principles calculations were performed based on DFT calculation as implemented in the VASP program during which the spin-orbit effect was neglected. These materials are direct bandgap material, which allow direct band to band transition with theoretically calculated tunable bandgap ranged 1.54 eV-2.33 eV (theoretically calculated) and 1.42-1.93 eV(experimentally determined). This suggests that these materials are suitable for photovoltaic and other optoelectronic device applications such as laser, light emitting diode and photovoltaic devices, which require direct band to band transitions.