Lead-free halide perovskite semiconductors are necessary due to the atmospheric instability and lead toxicity associated with the 3D lead halide perovskites. However, a stable lead-free perovskite with an ideal bandgap (1.2-1.4 eV) for photovoltaics is still missing. In this work, we synthesized organic-inorganic gold halide double perovskites ((CH3NH3)2Au2X6, X = Br, I) through a solution-processed route that offers an ideal direct bandgap for photovoltaic applications. Density functional theory calculations confirm the direct nature of bandgap nature with reasonable absorption coefficients in the visible range and excellent charge transport properties. In addition, the Au-halide perovskites show high chemical stability and photoresponse. These combined properties demonstrate that Au-based halide perovskites can be a promising group of compounds for optoelectronic applications.

Direct-bandgap Mixed-valence Organic-inorganic Gold Perovskite as Visible Light Absorber

Silver bismuth iodide has been studied comprehensively for its potential as light harvesters, owing to their low toxicity and environment conviviality. However, they often suffer with low efficiencies as compared to conventional light harvesters and hence there is a broad room for improvement. Here we propose doping the standard AgBiI4 composition with tin (Sn), to improve the relative absorbance and thereby potentially improving the efficiencies. It is observed that the addition of Sn did not alter the structural properties significantly, while it works on the orientation of the crystal growth during thin film synthesis, leading to ordered and uniform films. An improvement in absorption coefficient was observed, which can be considered to improve the performances of devices fabricated with AgBiI4 as light harvesters.

Biplab Ghosh

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