  Owing to the energy shortages and various severe adverse effects of
traditional fossil fuel power generation mechanisms, photovoltaic and
thermoelectric materials are considered as the potential candidates for
building non-traditional, efficient, and eco-friendly power generation
portfolios. Lead-based perovskites have emerged as highly efficient, abundantly
available, and low-cost materials for such applications but there are two major
challenges i.e. chemical instability and the danger of toxic lead leaching that
can badly affect both the environment and human health. Therefore, in search of
lead-free perovskites, the replacement of lead with eco-friendly elements like
bismuth and sodium may be a good strategy. Bismuth has very similar electronic
properties as that of lead so it gives very efficient perovskites. Therefore,
double perovskites containg Bi element X$_2$NaBiCl$_6$ (X=Cs, Rb, K) are
explored here in terms of the structural, opto-electronic , and thermoelectric
properties using the first-principles approach. The materials are attractive
for optoelectronic applications such as ultraviolet sensors and detectors due
to the prominent absorption peaks in ultraviolet region (10eV-30eV), low
reflection (5-7%), and high optical conductivity. In addition to the alluring
optoelectronic features, the compounds under study have figure of merit being
close to unity so these are also promising for thermoelectric applications.
