Halogen Bonding in Perovskite Solar Cells: A New Tool for Improving Solar Energy Conversion

Abstract

Hybrid organic–inorganic halide perovskites (HOIHPs) have recently emerged as a flourishing area of research. Their easy and low‐cost production and their unique optoelectronic properties make them promising materials for many applications. In particular, HOIHPs hold great potential for next‐generation solar cells. However, their practical implementation is still hindered by their poor stability in air and moisture, which is responsible for their short lifetime. Optimizing the chemical composition of materials and exploiting non‐covalent interactions for interfacial and defects engineering, as well as defect passivation, are efficient routes towards enhancing the overall efficiency and stability of perovskite solar cells (PSCs). Due to the rich halogen chemistry of HOIHPs, exploiting halogen bonding, in particular, may pave the way towards the development of highly stable PSCs. Improved crystallization and stability, reduction of the surface trap states, and the possibility of forming ordered structures have already been preliminarily demonstrated.

Green-Solvent-Processable Low-Cost Fluorinated Hole Contacts with Optimized Buried Interface for Highly Efficient Perovskite Solar Cells

“…Moreover, the 19 F NMR characterizations of the molecules before and after mixing with PbI 2 were conducted, as shown in Figure . Apparently, the upfield shift of F peaks for both FMPA–BT-CA and 2FMPA–BT-CA were observed, which may be ascribed to the formation of halogen bonding between F atoms and iodine (I) atoms in PbI 2 since the heavy iodine atoms could lead to a higher electron cloud density of F atoms . Therefore, we speculated that apart from the coordination effect between CA groups and Pb defects, the additional F atoms can further contribute to the interactions with free I – ions, which should enhance the passivation effect toward the buried interface of perovskite…”

“…Apparently, the upfield shift of F peaks for both FMPA−BT-CA and 2FMPA−BT-CA were observed, which may be ascribed to the formation of halogen bonding between F atoms and iodine (I) atoms in PbI 2 since the heavy iodine atoms could lead to a higher electron cloud density of F atoms. 41 Therefore, we speculated that apart from the coordination effect between CA groups and Pb defects, the additional F atoms can further contribute to the interactions with free I − ions, which should enhance the passivation effect toward the buried interface of perovskite. 42 It is well known that the surface properties of hole contacts will profoundly affect the growth of perovskite in p-i-n PSCs.…”

Halogen Bonding Involving Gold Nucleophiles in Different Oxidation States

“…According to the recently refined IUPAC recommendations, “in XB, the electrophilic region of a halogen atom (σ-hole) attractively interacts with any nucleophilic region (or regions in cases of bi- , or polyfurcated XB); the electrophilic region is not necessarily electropositive, but it should be less electronegative than the partner”. This type of noncovalent interactions − has found applications in various fields of chemical science, such as supramolecular chemistry, − crystal engineering, , drug design, − stabilization of explosives, noncovalent catalysis, − and polymer chemistry . Predominantly, XB acceptors span electronegative nonmetal elements featuring lone pair(s) [abbreviated as LP(s)] as basicity functions. ,− …”

Exploring halogen⋯halogen interactions in supramolecular self-assemblies of BODIPY networks

“…Noncovalent interactions, such as hydrogen bonding (HB), halogen bonding (XB), electrostatic, dipole-dipole and van der Waals interactions, represent an essential set of tools for the building of supramolecular architectures with precisely controlled structures and functions. [1][2][3][4][5][6] Thanks to the dynamic and reversible properties of noncovalent interactions, supramolecular assemblies have been used in widespread applications such as catalysis, [7][8][9][10] solar cells, [11][12][13] crystal engineering, 14,15 sensors, 16,17 and stimuli-responsive and selfhealing materials. [18][19][20][21][22][23] Among these interactions, XB has become increasingly attractive as a routine and predictable tool in supramolecular chemistry, due to its highly directional nature, significant strength, and tunable length.…”