Constructing Stable and Potentially High-Performance Hybrid Organic-Inorganic Perovskites with “Unstable” Cations

Abstract

<jats:p>A new family of functional hybrid organic-inorganic perovskites (HOIPs) is theoretically designed based on the following chemical insights: when a proton is adhered to molecules like water or ethanol, the newly formed larger-sized cations (e.g., H<jats:sub>5</jats:sub>O<jats:sub>2</jats:sub><jats:sup>+</jats:sup>, C<jats:sub>2</jats:sub>H<jats:sub>5</jats:sub>OH<jats:sub>2</jats:sub><jats:sup>+</jats:sup>, and CH<jats:sub>3</jats:sub>SH<jats:sup>+</jats:sup>) entail low electron affinities mimicking superalkalis; they are conjugated acids of weak bases that cannot survive in solution, while their chemistry behavior in the HOIP frameworks, however, may be markedly different due to greatly enhanced cohesive energies of the proton, which facilitate the formation of new HOIPs. First-principles computations show that the putative formation reactions for these newly designed HOIPs typically release much more energy compared with the prevailing HOIP MAPbI<jats:sub>3</jats:sub>, suggesting the likelihood of facile solution-based fabrications, while the suppression of reverse formation suggests that the humidity stability may be markedly enhanced. During their formations, halide acids are unlikely to react with ethanol or methanethiol without the presence of metal halides, a condition further favoring their stability. The proposed structure of (H<jats:sub>5</jats:sub>O<jats:sub>2</jats:sub>)PbI<jats:sub>3</jats:sub> may also clarify the origin of the long-speculated existence of HPbI<jats:sub>3</jats:sub>. Importantly, density functional theory computations suggest that many of these HOIPs possess not only direct bandgaps with values within the optimal range for solar light absorbing but also more desirable optical absorption spectra than that of MAPbI<jats:sub>3</jats:sub>, where their ferroelectric polarizations also benefit photovoltaics. The stability and photovoltaic efficiency may be even further improved for the newly designed two-dimensional (2D) HOIPs and 2D/3D hybrid HOIP structures.</jats:p>

Bimetallic superalkali substitution in the CsPbBr3 perovskite: Pseudocubic phases and tunable bandgap

“…However, we acknowledge that the accuracy of DFT calculations can be enhanced by using dispersion corrections when estimating dispersion effects in perovskite systems. [21][22][23] All calculations have been performed spin-polarized and without symmetry constraints. Electronic wave functions were expanded to an energy cutoff of 650 eV.…”

Two-Dimensional van der Waals Ferroelectrics: Scientific and Technological Opportunities

“…Note that the record for photovoltaic efficiency, higher than 25%, was achieved in hybrid perovskites. , Although those 2D structures possess chemical stability higher than that of the well-known MAPbI 3 , their band gaps are over 3 eV, which is not within the desirable solar range. A potential ideal candidate is 2D (C 2 H 5 OH 2 ) 2 SnI 4 , which was predicted to possess a band gap of ∼1.7 eV (Figure b) and a switchable in-plane polarization of 1.2 × 10 –10 C/m. Li et al predicted that 2D carbon nitrides may enable “facile functionalization”, forming FE structures (see Figure c) when wetted by a solution of metal halides with mobile cations/anions, with each cavity spontaneously functionalized by a unit of metal halide inside.…”

Rational Design of a Super-Alkali Compound with Reversible Photoluminescence

“…Also, the cationic part of H 5 O 2 + Cl – , the so-called Zundel-type cation H 5 O 2 + , − is a very important hydrated proton ubiquitous in solutions and water–solid interfaces, and the incorporation of this cation into the host crystal will enhance host–guest interaction through hydrogen bonding. More importantly, it is reported that once bonded with water molecules, the proton behaves like alkali cations with a much-reduced electron affinity. , This value-added feature along with the expanded ion radius , is of particular importance for the formation of new LDMHs.…”