Investigating the effect of lead substitution on the optical, electrical, and photoresponse properties of Quasi-2D double perovskites

Quasi-2-dimensional (2D) halide perovskites have recently attracted attention due to their higher operational stability as alternatives to 3-dimensional (3D) perovskites having exceptional optoelectronic and charge transport properties. To reduce the lead content, here following the double perovskite approach lead is substituted with silver and bismuth simultaneously, and three quasi-2D perovskites, with general formula (C7H10N)(2)Pb((1-2x))AgxBixBr4, (0 <= x <= 0.5) were prepared. The optical studies show that the partially lead substituted sample has the lowest optical band gap, aptly supported by the theoretical calculations. The powder X-ray diffraction technique along with field-emission scanning electron microscopy suggests enhancement in crystallinity along with the decrease in grain boundaries with the substitution of lead. The improvement in crystallinity with concomitant reduction in grain boundaries has led to the decrease in point defects as identified from the positron annihilation lifetime spectroscopy and coincidence Doppler broadening analysis. The tuned band gap, improved crystal quality along with lower defects jointly contributed to the enhancement in electrical properties of the perovskites with varying lead percentages. Finally, the photoresponse of all the materials was studied after fabricating metal (Al)-semiconductor (MS) junction thin film photodetector devices.