Thousand‐fold Conductivity Increase in 2D Perovskites by Polydiacetylene Incorporation and Doping

Abstract

Two-dimensional (2D) organic-inorganic perovskites have rapidly become an attractive alternative to traditional three-dimensional (3D) perovskite solar-cell absorbers owing to their improved stability and processability. Despite their advantages, the insulating nature of the organic cations and diminished light absorption limit their overall performance. Herein, it is demonstrated that the incorporation of conjugated diynes in hybrid 2D perovskites, and subsequent thermal treatment results in the formation of 2D perovskites that incorporate polydiacetylenes in their structure. Furthermore, it is shown that oxygen or iodine doping results in the formation of stable radicals within the material alongside a drastic shift of the band gap from 3.0 to 1.4 eV and in-plane conductivity improvements of up to three orders of magnitude, which lead to record conductivities for 2D halide perovskites (n=1).

Two‐Dimensional Halide Perovskites in Solar Cells: 2D or not 2D?

“…Even so, the organic cations can also have some influence in the optoelectronic properties of the materials, for example, the organic spacer has significant influence on the M–X–M angle, which when deviating from the ideal 180° alters the band structure, increasing the bandgap . Another example is the use of haloalkanes, which by means of halogen bonding with the inorganic layers can reduce the bandgap of layered perovskites by almost 0.3 eV relative to their non‐halogenated counterparts . More recent examples include the use of highly conjugated polymers and aromatic cations …”

“…Stupp and co‐workers demonstrated that in compounds of the type (Ar−O−(CH 2 ) 3 −NH 3 )PbI 4 (where Ar=perylene, pyrene, or naphthalene) the inclusion of the cation improves the stability, the out‐of‐plane electronic conductivity, and the overall performance of the photovoltaic device . Other example of organic cations that can affect the optoelectronic properties of 2D perovskites is the incorporation of ammonium diynes that upon heating generate highly conjugated polymers inside the perovskite crystal, thereby improving their optical absorption, electronic conductivity, and potentially the mechanical properties of the materials and devices themselves . Another interesting case is the use anilinium compounds in perovskites with n ≥2, as the inclusion of this cation showed important red‐shifting in the band edge and reduced exciton binding energies …”

“…These interactions may include hydrogen and halogen bonds as well as p-p and van der Waalsi nteractions.W hile many of these interactions are weak,i nm ore complex organic moieties with multiple functional groups the effects of the interactions alongt he longitudinal axis of the organic molecule are additive and can, therefore, play ac rucial structure-directing role. [12] Importantly, the perovskite framework is highly tolerant of organic functional groups such as thiol, [13] carboxyl, [14] alkenyl, [15] alkynyl, [16] diyn, [17] and many others. [10,18,19] The tolerance for such aw ide varietyo fs izes and functional groups in the organic cations, along with the possibility to change the metal, halides, and thickness of the inorganic sheets (n value), make the possible 2D hybrid perovskites virtually infinite, and yeto nly af ew hundred perovskite structuresh ave been reported,a nd only a small fraction of those have been used in as olar cell.…”

Reversible Thermochromism and Strong Ferromagnetism in Two‐Dimensional Hybrid Perovskites

“…Importantly, the process of conductivity changed with temperature is reversible, the conductivity is reduced when the temperature is lowered (Figure S13). In previous work, researchers have tried to tune the conductivity of perovskite via changing the organic moieties, and obtained conductivity change can only cover no more than four orders of magnitude . In comparison, the conductivity change of (BED) 2 CuCl 6 spans close to six orders of magnitude, which is the highest value for perovskite materials.…”

Thousand‐fold Conductivity Increase in 2D Perovskites by Polydiacetylene Incorporation and Doping

“…Pb-Br octahedra:green, Pb:green, Br:brown, N: blue, C: gray.Hydrogen atoms are omitted for clarity [30]. Pb-Br octahedra:green, Pb:green, Br:brown, N: blue, C: gray.Hydrogen atoms are omitted for clarity [30].…”