First‐principles study ofCs₂Ti_1−xM_xBr₆(M = Pb, Sn) and numerical simulation of the solar cells based onCs₂Ti_0.25Sn_0.75Br₆perovskite

Abstract

The impact of partial substitution by replacing 'Ti' atom with Pb and Sn respectively in vacancy ordered perovskites Cs 2 Ti 1−x M x Br 6 (M = Pb, Sn) has been studied using density functional theory calculations. Our results indicate the unexpected presence of intermediate bands (IBs) in the forbidden gap of electronic structure for lead substituted compounds (x = 0.25, 0.5, 0.75) Cs 2 Ti 1 −x Pb x Br 6. These IBs located above the valence band could be tuned from 0.60 to 0.45 eV with appropriate Pb doping percentage. The nature of the band gap for the Sn substituted Cs 2 Ti 0.25 Sn 0.75 Br 6 compound was found to become direct as the highly dispersive Sn impurity bands from the conduction band minimum. Also, the negative formation energy of Pb and Sn doped compositions ensures the stable nature of these compounds. The tunable nature of IBs in the Pb substituted Cs 2 Ti 1−x Pb x Br 6 compounds suggests that they could become potential solar absorber semiconductor for IB solar cells (IBSCs), however, further tuning could be required to realize them. Also, the electronic band structure of lead-free composition Cs 2 Ti 0.25 Sn 0.75 Br 6 exhibits a direct band gap of 1.50 eV, which could be a promising candidate for single-junction caesium-titanium perovskite-based solar cells. Based on this result, the efficiency of perovskite solar cell based on the lead-free composition Cs 2 Ti 0.25 Sn 0.75 Br 6 has been calculated by solar cell capacitance simulator (SCAPS)-1D software. The effect of various physical parameters on the photovoltaic performance of Cs 2 Ti 0.25 Sn 0.75 Br 6 solar cells has been investigated to obtain the highest efficiency of the solar cells. The optimized power conversion efficiency of the solar cell based on the planar device configuration FTO/c-TiO 2 (20 nm)/Cs 2 Ti 0.25 Sn 0.75 Br 6 (600 nm)/Cu 2 O (200 nm)/Au is 22.13% with V oc = 1.02 V, J sc = 26.24 mA/cm 2 , and FF = 82.24%. These results could pave the way towards environmentally friendly perovskite solar cells.

Titanium‐Based Vacancy‐Ordered Double Halide Family in Perovskite Solar Cells

“…[ 44 ] In achieving an ideal bandgap while catering to the high and indirect bandgap issue of Cs 2 TiBr 6 , Ti can partially be replaced with another cation. Through DFT calculations (VASP), Shrivastava et al studied the impact of partial substitution of the Ti atom with other cations, specifically Sn and Pb, resulting in compounds with a chemical formula Cs 2 Ti 1– x M x Br 6 [ 45 ] where M = Sn and Pb. Pb substitution or doping will not be reviewed here.…”

“…The structure is derived from conventional perovskites by doubling the ABX 3 unit cell along all three crystallographic axes and removing every other B-site cation to form a face-centered lattice of isolated BX 6 octahedral units bridged by A-site cations in the void (vacancy-ordered DHPs). [18,19] The absence of one B-site cation in the double perovskite A 2 B 2 X 6 yields the vacancy-ordered double perovskite structure, [20] as illustrated in the schematic diagram in Figure 2. The A 2 BX 6 structure shows similar features to ABX 3 perovskites, mostly of cubic structures.…”

Acid‐ and Base‐Stable Cs2Pt(Cl,Br)6 Vacancy‐Ordered Double Perovskites and Their Core–Shell Heterostructures for Solar Water Oxidation

“…It is well known that perovskites based on mixed halides and metal cations offer a wide range of tunability in their optoelectronic properties including absorption, and photoluminescence (PL). [47,48] In this work, mixed halide tunability of Cs 2 PtCl 6Àx Br x by anion exchange technique using bromide salt solutions was investigated. The Cs 2 PtCl 6 is mixed with 1.5 M LiBr solution and the anion exchange studies were carried out over a period of time.…”

“…It is well known that perovskites based on mixed halides and metal cations offer a wide range of tunability in their optoelectronic properties including absorption, and photoluminescence (PL). [ 47,48 ]…”