Organic-inorganic lead halide perovskites have rapidly emerged over the last few decades as photovoltaic materials due to their high power conversion efficiency (PCE). The high efficiency of these kinds of semiconducting materials is attributed to some of the useful and interesting properties, viz., high absorption coefficients, long carrier lifetimes, diffusion lengths and high charge carrier mobility, etc. But the toxicological nature and the instability of lead halide perovskites limit their commercialization. In this regard, to provide a kind of solution, we have designed five different lead (Pb) free Ga and In based halide perovskites ((AM)$_3$(Ga$_$In$_$)$_2$I$_9$, (MA)$_3$(Ga$_$In$_$)$_2$I$_9$, (DMA)$_3$(Ga$_$In$_$)$_2$I$_9$, (TMA)$_3$(Ga$_$In$_$)$_2$I$_9$, and (TTMA)$_3$(Ga$_$In$_$)$_2$I$_9$) having the general formula A$_3$B$_2$X$_9$. The trivalent metal cation based A$_3$B$_2$X$_9$ type perovskite materials exhibit non-toxicity and more ambient stability compared to the conventional ABX$_3$ type perovskite materials. Structural parameter analysis shows that the designed perovskite materials are capable of forming structurally and thermodynamically stable materials. Optical properties study reveals that all the designed compounds possess absorption maxima within the visible range of the electromagnetic spectrum. In addition, among the studied compounds, (TTMA)$_3$(Ga$_$In$_$)$_2$I$_9$ shows the highest theoretical PCE of 16.43\%.

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