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).

Thioureas are an important scaffold in organocatalysis because of their ability to form hydrogen bonds that activate substrates and fix them in a defined position, which allows a given reaction to occur. Structures that enhance the acidity of the thiourea are usually used to increase the hydrogen-bonding properties, such as 3,5-bis(trifluoromethyl)phenyl and boronate ureas. Herein, we report the synthesis of bifunctional thioureas with a chiral moiety that include either a trifluoromethyl or methyl group. Their catalytic performance in representative Michael addition reactions was used in an effort to compare the electronic effects of the fluorination at the methyl group. The observed differences concerning yields and ee values cannot be attributed solely to the different steric environments; theoretical results indicate distinct interactions within the corresponding transition states. The calculated transition states show that the fluorinated catalysts have stronger N-H···O and C-H···F hydrogen bonds, while the nonfluorinated systems have C-H···π contacts. These results have shown that a variety of hydrogen-bonding interactions are important in determining the yield and selectivity of thiourea organocatalysis. These details can be further exploited in catalyst design.

Tw o-dimensional (2D) organic-inorganic perovskites have rapidly become an attractive alternative to traditional three-dimensional (3D) perovskite solar-cell absorbers owingt ot heir improved stability and processability.D espite their advantages,t he insulating nature of the organic cations and diminished light absorption limit their overall performance.H erein, it is demonstrated that the incorporation of conjugated diynes in hybrid 2D perovskites,a nd subsequent thermal treatment results in the formation of 2D perovskites that incorporate polydiacetylenes in their structure.F urthermore,i ti ss hown that oxygen or iodine doping results in the formation of stable radicals within the material alongside adrastic 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 recordc onductivities for 2D halide perovskites (n = 1). Two-dimensional (2D) organic-inorganic hybrid perovskiteshave recently attracted attention as viable alternatives to three-dimensional (3D) perovskites solar cells absorbers such as MAPbI 3 (MA = methylammonium) and related materials. Compared to the 3D analogues,2 Dp erovskites have shown improved processability and stability towards water and light. [1][2][3][4][5][6] This can be easily rationalized when considering the hydrophobic nature of the cations that replace the volatile and hydrophilic methylammonium. [1][2][3][4][5] Thei nsulating nature of the organic cations in 2D perovskites also disrupts the electronic structure of these materials,w hich leads to diminished light absorption (larger band gaps) and conductivities.T his peculiar electronic structure,w hich consists of alternating semiconducting and insulating layers,h as been described as aq uantum-well structure. [7][8][9] In this work, we describe how the incorporation of conjugated diynes into 2D lead halide perovskites and subsequent thermal treatment results in the topochemical formation of 2D lead halide perovskites that incorporate polydiacetylenes into their structure.F urthermore,w es how that by oxygen or iodine doping we can generate additional carriers that generate important changes in the properties of these materials, shifting the optical band gap from 3.0 to 1.4 eV and improving the conductivity by up to three orders of magnitude, effectively inverting the traditional quantum-well structure (Figure 1a,b).Seminal work by Tieke and collaborators [10][11][12][13] showed that irradiating 2D perovskites with unsaturated organic cations resulted in the topochemical polymerization of such cations with retention of the 2D hybrid perovskite structure.M ost studies by Tieke however,f ocused on the use of cadmium chloride layers and diene monomers,w hich have large band gaps and form polymers without notable electronic properties.L ater, Takeoka and co-workers incorporated polydiacetylenes in lead halide perovskites;however, they used gamma radiation to induce polymerization, which makes this technique unpractical for most applications. [14] Other attemp...

Thiourea organocatalysts with a chiral group containing a trifluoromethyl moiety have better hydrogen bonding properties. However, not all reactions catalysed by bifunctional catalysts are enhanced by stronger NH acidity.

Two‐dimensional (2D) organic–inorganic hybrid perovskites have rapidly become an attractive alternative to three‐dimensional (3D) perovskites as solar cell absorbers, owing to their improved stability, versatility, and ease of processing. Despite their advantages, the insulating nature of the organic cations makes these materials have lower absorbing and conducting properties, resulting in lower device efficiencies. A way to circumvent these issues is the integration of functional molecules that help mitigate these limitations. In this study, six new perovskites composed of three distinct diynes are synthesized, all of which can be thermally polymerized to form conjugated polymers within the perovskite layers. The incorporation of conjugated polymers results in drastic changes in these materials’ optoelectronic properties and their overall stability. Furthermore, depending on the nature of the diyne and the inorganic layers, the materials show varying polymerization yields, optical bandgaps, and charge carrier densities. These results afford significant insight into the chemical nature of the polymerized species and thus highlight the versatility of this approach to post‐synthetically generate conducting polymers within the layers of 2D perovskites, paving the way toward their use in optoelectronic devices.