Lead halide perovskites (LHPs) have demonstrated enormous potentials in a wide range of application including optoelectronic devices and photocatalysis due to their exceptional optical and electronic properties. However, long-term stability and toxicity of LHPs are the main limiting factor towards their practical application. In this view, lead-free halide double perovskites (DPs)_, are under spotlight due to their superior material stability and attractive optoelectronic properties. Nevertheless, relatively larger band gap (> 4eV) of Cs₂AInCl₆ (A = Ag Na) DPs materials are the main bottlenecks towards their light harvesting application including photocatalysis.^[1,2] Moreover, the severe charge recombination and presence of fewer catalytic active sites are considered as main limiting factor towards efficient photocatalytic CO₂ reduction.^[3] The doping and compositional engineering of Cs₂AInCl₆ (A = Ag, Na) DPs are under spotlight due to their dopant-induced extended light harvesting abilities and enhanced self-trapped excitons (STEs) emission for a wide range of applications including optoelectronic devices and photocatalysis.^[1,2,4,5] Furthermore, the catalytic performances of lead-free DP NCs can be further improve by coupling them with two-dimensional (2D) nanosheet (NSs) with desirable energy offset. The  type II heterojunction between DP NCs and 2D NSs can enhance the charge separation and inhibit the charge recombination. It is well established that 2D ultrathin g-C₃N₄ NSs possess large surface area, rich density of catalytic active sites, and superior charge transport. All these features are advantageous for photocatalytic CO₂ reduction. In particular, the interface between Cs₂AgBiBr₆ DP NCs/ g-C₃N₄ 2D NSs would significantly facilitate the charge transfer and separation of photogenerated excitons.

In this talk, I will present the colloidal synthesis of iron-doped Cs₂AInCl₆ (A = Ag, Na) DP NCs, which resulted in a significant extension of absorption edge into the visible part of spectrum. Furthermore, I will discuss how iron doping allows precise tuning of the optical band gap and electronic band structures of the resulting DP NCs and their application in photocatalytic CO₂ reduction. Next, I will also explore our recent results on multifacet spheroidal Cs₂AgBiBr₆ DP NCs/g-C₃N₄ NSs heterostructure, including colloidal synthesis, optical properties and their application in visible-light driven photocatalytic CO₂ reduction.