Bandgap Engineering of Lead-Free Double Perovskite Cs₂AgInCl₆ Nanocrystals via Cu²⁺-Doping

Abstract

Lead-free double perovskites (DPs) with excellent moisture, light, and heat stability have been explored as alternatives to toxic lead halide perovskite (APbX 3 ) (A for monovalent cation and X for Cl, Br, or I). However, the bandgaps of the current DPs are generally larger and either indirect or direct forbidden, which leads to weak visible light absorption and limitation for photovoltaic and other optoelectronic applications. Herein, we demonstrate the first synthesis of Cu 2+ -doped Cs 2 AgInCl 6 double perovskite nanocrystals via a facile hot-injection solution approach. The electronic bandgap can be dramatically tuned from ∼3.60 eV (Cs 2 AgInCl 6 , parent) to ∼2.19 eV (Cu 2+ -doped Cs 2 AgInCl 6 ) by varying the Cu 2+ doping amount. We conclude that the decrease of bandgap is attributed to the overlap of the Agd/In-p/Cl-p orbitals and the Cu-3d orbitals in the valence band. The wide tunability of the optical and electronic properties makes Cu 2+ -Doped Cs 2 AgInCl 6 DP NCs promising candidates for future optoelectronic device applications.

Experimental and Theoretical Investigation of the Structural and Opto‐electronic Properties of Fe‐Doped Lead‐Free Cs2AgBiCl6 Double Perovskite

“…The binding energy of all the elements is slightly shifted at higher values than the reported one, demonstrating that the stronger M‐Cl interaction in the [BiCl 6 ] 3− and [AgCl 6 ] 5− octahedra and leads to differing the chemical environment around Bi, Ag, and Cs on Fe‐incorporation. The results are analogous to that of earlier reported systems [46–48] . These results confirm the effective doping of Fe in Cs 2 AgBiCl 6 double perovskite material.…”

“…The band gap reduction after Fe‐doping may be due to the overlap of the Ag‐d/Cl‐p orbital and the Fe‐3d orbital during the construction of the valence band and new VBM shifting towards a higher energy level as revealed by DFT calculations (Figure 8). A similar result has been observed in Cu‐doped Cs 2 AgInCl 6 , Sb‐doped Cs 2 AgBiBr 6 and Ti‐doped Cs 2 AgBiBr 6 [48, 50] . The decrease in band gap suggests that the Fe‐doped Cs 2 AgBiBr 6 double perovskite material is a more suitable absorber for tandem solar device applications.…”

“…The PL decay time of the Fe‐doped Cs 2 AgBiCl 6 double perovskite is reduced as compared to the undoped Cs 2 AgBiCl 6 double perovskite materials [37] . It may be the enhancement in the non‐radiative recombination rate [48] . The emission decay traces can be well fitted to bi‐exponential function, [53–55] …”

Enhanced visible light absorption in layered Cs3Bi2Br9 through mixed-valence Sn(ii)/Sn(iv) doping

“…The wide range of ions that can be incorporated on both the cation and anion sites of an choice of composition. 2 Several strategies have been employed, from alloying on the halide site, 8,[23][24][25] which usually produces a band gap response similar to that seen in the perovskites, to doping on the B-metal site, which may lead to introduction of filled states within the band gap, 26,27 or band bowing. [26][27][28] Recently, Ghosh et al studied a mixed valence perovskite (CH 3 NH 3 )AuBr 3 , containing Au(I) and Au(III), which resulted in significant visible light absorption.…”

Lead‐Free Halide Double Perovskite Nanocrystals for Light‐Emitting Applications: Strategies for Boosting Efficiency and Stability

“…The Cu 2+ as dopant was successfully incorporated into the lattice of Cs 2 AgInCl 6 nanocrystals, which could reduce bandgap from 3.60 to 2.19 eV with the increase of the Cu 2+ doping content from 0% to 3.4% due to the contribution of Cu‐3d orbitals in the VBM. [ 161 ] Similarly, Cu 2+ doped Cs 2 AgSbCl 6 HDPs can significantly change bandgap, in which the bandgaps decreased from 2.6 to 1.02 eV after Cu 2+ doping amount increased from 0 to 0.1. [ 162 ] However, the PL property of Cu 2+ doping HDPs have not obviously improved.…”