Stability and toxicity issues of hybrid lead iodide perovskite MAPbI_3 necessitate the hunt for potential alternatives. Here, we shed new light on promising photovoltaic properties of gold mixed valence halide perovskites Cs_2Au_2X_6 (X=I, Br, Cl). They satisfy the fundamental requirements such as non-toxicity, better stability, band gap in visible range, low excitonic binding energy etc. Our study shows favorable electronic structure resulting in high optical transition strength, thus sharp rise in absorption spectra near band gap. This, in turn, yields very high short circuit current density and hence higher simulated efficiency compared to MAPbI_3. However, careful investigation of defect physics reveals the possibility of deep level defects (such as V_X, V_Cs, X_Au, X_Cs, Au_i, Au_X, X= I, Br), depending on the growth condition. These can act as carrier traps and become detrimental to photovoltaic performance. The present study should help to take necessary precautions in synthesizing these compounds in a controlled chemical environment which can minimize the performance limiting defects and pave the way for future studies on this class of materials.