Cesium-Coated Halide Perovskites as a Photocathode Material: Modeling Insights

Abstract

Photocathodes emit electrons when illuminated, a process utilized across many technologies. Cutting-edge applications require a set of operating conditions that are not met with current photocathode materials. Meanwhile, halide perovskites have been studied extensively and have shown a lot of promise for a wide variety of optoelectronic applications. Well-documented halide perovskite properties such as inexpensive growth techniques, improved carrier mobility, low trap density, and tunable direct band gaps make them promising candidates for next-generation photocathode materials. Here, we use density functional theory to explore the possible application of pure inorganic perovskites (CsPbBr3 and CsPbI3) as photocathodes. It is determined that the addition of a Cs coating improved the performance by lowering the work function anywhere between 1.5 and 3 eV depending on the material, crystal surface, and surface coverage. A phenomenological model, modified from that developed by Gyftopoulos and Levine, is used to predict the reduction in work function with Cs coverage. The results of this work aim to guide the further experimental development of Cs-coated halide perovskites for photocathode materials.

A Theoretical Framework for Microscopic Surface and Interface Dipoles, Work Functions, and Valence Band Alignments in 2D and 3D Halide Perovskite Heterostructures

“…It has recently been demonstrated that by depositing monolayers of Cs on top of halide perovskites, the electron emission efficiency was improved, and the improvement was attributed to a change of sign of the electron affinity, which translates into a diminishing work function. Work function shifts obtained by DFT techniques can be compared to dedicated phenomenological models, but we show here that the atomistic origin can be directly analyzed within the general theoretical framework proposed in the present work. To shed more light on this effect, we placed a monolayer of Cs (each monolayer contains 2 Cs atoms for 2 terminal I atoms) on top of either side of the relaxed surface layers of both CsI- and PbI 2 -terminated CsPbI 3 slabs (Figure S7).…”

Theoretical study on photoelectric properties of ferroelectric photovoltaic perovskite CsGeBr3 based on first-principle calculations

“…To investigate the dynamic stability of the ferroelectric phase of CsGeBr 3 under different compressive strains, we calculate the phonon dispersion via the phony package [67,68]. As shown in figure 7, all the phonon dispersions have no imaginary frequency, which indicates that the structure of ferroelectric perovskite CsGeBr 3 is dynamically stable under the applied compressive strains in this work.…”

“…The vacuum space was set at 15 Å to separate the interactions between adjacent slabs. Considering the influence of surface termination and coating thickness on the work function, we choose 4 layers of slab surfaces along the [001] direction [68]. We measure the magnitude of coulomb potential of the intrinsic electric field of ferroelectric materials as Ψ = ΔΦ/e, where is the variance in electrostatic potential energy, and e represents the charge [39].…”

Halide perovskites and perovskite related materials for particle radiation detection

“…These values were also consistent with previous reports. 136,137 Beside inorganic perovskites, Liu et al also tested organicinorganic halide perovskites, including triple cation FA 0.7 MA 0.25 Cs 0.05 PbI 3 and Ruddlesden-Popper layered perovskites (BA 2 MA 1 Pb 2 I 7 and BA 2 MA 4 Pb 5 I 16 ). 136 (Fig.…”

“…A theoretical study of the origin of the reduced work function of Cs-coated halide perovskites was carried out by Lewis et al 137 They used density functional theory (DFT) to investigate Cs-coated halide perovskites. A single-layer Cs coating can reduce the work function of CsPbBr 3 and CsPbI 3 [001] surfaces from ∼4 eV to ∼2.1 eV, and a double-layer Cs coating further lowered the work function to 2.0 eV and 1.8 eV, respectively.…”