Structural, Thermodynamical and Electronic Properties of All-Inorganic Lead Halide Perovskites

Abstract

Organic-inorganic hybrid lead halide perovskites have emerged as the most promising materials in the field of optoelectronics due to their unique electronic and optical properties. However, the poor long-term material and device stabilities of these materials have limited their practical application. Compared to organic-inorganic hybrid perovskites, all-inorganic halide perovskites like CsPbX3 (X = Cl, Br, I) show enhanced thermal stability and the potential to resolve the issue of instability. Nevertheless, the structural and physical properties of allinorganic CsPbX3 halide perovskites with multiple structural polymorphs are still under debate. A recent research article on CsPbI3 reported the wrongly indexed the XRD pattern of γ-CsPbI3 as α-CsPbI3. Consequently, the band gap of γ-CsPbI3 (1.73 eV) was erroneously designated for α-CsPbI3. Therefore, there is a need for systematic research on the relationship between the structural features and electronic properties of CsPbX3. Here, we present a comprehensive theoretical study of the structural, thermodynamical and electronic properties of three polymorphic phases, α-, β-, and γ-CsPbX3. The space group of α-, β-, and γ-CsPbX3 are Pm3 m, P4/mbm, and Pnma, respectively. First-principles calculations indicate that the phase transition from the hightemperature α-phase to the low-temperature β-phase and then to the γ phase is accompanied by an increase in the degree of PbX6 octahedral distortion. The zero-temperature energetic calculations reveal that the γ-phase is the most stable. This is consistent with the fact that experimentally, the γ-phase is stabilized at a relatively low temperature. Analysis of the electronic properties indicates that all the CsPbX3 perovskites exhibit a direct-gap nature and the band gap values increase from α to β, and then to the γ phase. From the analysis of the orbital hybridization near the band gap edges, the increase can be explained by the downshift of the valence band edges caused by the gradual weakening of the Pb-X chemical bond. Among all the phases, the strongest Pb-X interaction in the α-phase leads to the most dispersive band-edge states and thus the smallest carrier effective masses, which are beneficial for carrier transport. Additionally, the band gaps decreased by changing the halogen type from Cl to Br and I under the same phase. this is a consequence of the increased X np orbital energies from Cl 3p to Br 4p and then to I 3p that leads to a high valence band edge for CsPbI3 and results in the smallest band gap. Our results provide deep understanding on the relationship between the physical properties and structural features of all-inorganic lead halide perovskites.

Metal Halide Semiconductors beyond Lead-Based Perovskites for Promising Optoelectronic Applications

“…For example, in low-dimensional materials, reasonable control over layer thickness can achieve tunable band gaps, owing to the strong quantum confinement effect . Furthermore, equivalent replacement with the same main-group elements is also an effective way to control the band gap. , It should be noted that for the same group elements having similar valence electronic configuration, a significant deviation in orbital contribution to the band edge is not expected. In addition, an alloying strategy is also widely used in band engineering.…”

Entropy-Driven Stabilization of Multielement Halide Double-Perovskite Alloys

“…Despite the rapid increase in power conversion efficiency (PCE) of lead halide perovskites, the ultimate commercialization of this emerging technology still faces some serious challenges, such as the toxicity of Pb and instability against moisture/air and temperature. Extensive research efforts have been performed to explore alternative nontoxic/low-toxicity and air-stable halide perovskites. − For example, one alternative is replacing toxic Pb with Sn/Ge to reduce the environmental toxicity of perovskites. Although spontaneous oxidation still exists, the current highest PCE of tin-based solar cells has reached 14.6% .…”

Modulating CsPbl3 crystallization by using diammonium agent for efficient solar cells

“…However, the poor thermal stability and moisture sensitivity of metal halide organic–inorganic hybrid perovskites make a significant obstacle to the practical application of PSCs due to the volatilization of organic groups and the weak hydrogen bonding between the organic cations and [PbI 6 ] 4− octahedra frameworks 10–12 . Recently, inorganic perovskites aroused tremendous attention because of their good thermal stability 13–17 . Black‐phased CsPbI 3 perovskite with a bandgap ( E g ) of approximately 1.7 eV could be an ideal light absorber for the development of efficient single‐junction solar cells or tandem solar cells to further increase the photovoltaic performance 18–21 .…”

“…[10][11][12] Recently, inorganic perovskites aroused tremendous attention because of their good thermal stability. [13][14][15][16][17] Black-phased CsPbI 3 perovskite with a bandgap (E g ) of approximately 1.7 eV could be an ideal light absorber for the development of efficient single-junction solar cells or tandem solar cells to further increase the photovoltaic performance. [18][19][20][21] In the last couple of years, even though the PCE of inorganic PSCs was largely improved, 22,23 their efficiency still largely lags behind the hybrid PSCs because of the large open-circuit voltage deficit, 24,25 which could be mainly assigned to the unsatisfied quality of inorganic perovskites, such as low black-phase stability, numerous defects, and poor crystallinity.…”