Conjugated Thiophene-Containing Polymer Zwitterions: Direct Synthesis and Thin Film Electronic Properties

Abstract

We report a direct and facile synthesis of novel conjugated polymeric zwitterions (CPZs) as a simple route to electronically active homopolymers and copolymers containing dipole-inducing pendent zwitterions. Sulfobetaine-containing polythiophenes (PTSB-1 and PTSB-2) and alternating thiophene–benzothiadiazoles (PTBTSB-1 and PTBTSB-2) were prepared and characterized relative to alkylated polymer analogues (POT- a -T and POT- a -BT). The polar zwitterionic side chains make these polymers hydrophilic and salt-responsive, with interesting electronic properties that depend on zwitterion distance from the conjugated polymer backbone (tether length), as characterized by UV–vis absorption and ultraviolet photoelectron spectroscopy (UPS). Close proximity (CH2 spacer) of the sulfobetaine groups to the polymer backbone results in increased ionization potential and enlarged band gaps of 2.19 and 2.04 eV for PTSB-1 and PTBTSB-1, respectively. On Au and Ag surfaces, the zwitterionic pendent groups significantly alter the work function due to the presence of an interfacial dipole, with the largest interfacial dipoles measuring −1.29 eV (PTBTSB-1/Au) and −0.69 eV (PTBTSB-1/Ag).

Structures and Synthesis of Zwitterionic Polymers

“…On the other hand, a large number of novel building blocks as well as polymer structures have evolved recently, too. This concerns to a lesser degree the nature of the zwitterionic moieties incorporated into the polymer, but mostly the nature of the polymer skeleton, including electronically conjugated ones [96][97][98][99][100][101][102][103][104][105], as well as the overall polymer architecture.…”

“…RDRP methods enable also the anchoring of polyzwitterions to surfaces by "grafting-through" [105] and "grafting-to" processes [193,203,[313][314][315][316][317]. In particular, the latter profits from the facile incorporation of reactive groups in special positions, e.g., in the center or at the ends of the polymers, that enable efficient attachment of the macromolecules onto the substrates.…”

“…Another classical step growth polymerization method applied to polyzwitterions is the condensation of silanols, yielding, e.g., mesoporous organosilica [381]. Recently, transition metal catalyzed couplings, such as Suzuki couplings, were shown to afford polyzwitterions, too (Figure 7c) [101,104,105]. Such conjugated zwitterionic polymers are particularly sought for electrical, optical, and optoelectronical devices.…”

Understanding Interface Engineering for High‐Performance Fullerene/Perovskite Planar Heterojunction Solar Cells

“…[ 56 ] The strengthened electric fi eld increases free charge generation and extraction effi ciency to enhance the short-circuit current density ( J SC ) and fi ll factor (FF). The interfacial dipole moreover increases the Φ offset between the two electrodes of the device, thus maximizing open-circuit voltage ( V OC ).…”

Raising efficiency of organic solar cells with electrotropic additives

“…Interlayer materials with dipolar amine [18][19][20] and zwitterionic sulfobetaine 21 functional groups have recently been introduced as effective solution-processible cathode modification layers, increasing PCE values of OPV devices and enabling utilization of high work function metals (Au, Ag, and Cu) as cathodes, potentially improving device lifetimes and eliminating vacuum deposition steps from the device fabrication process. The ability of amine-and sulfobetaine-functionalized interlayers to reduce the work function of metal electrodes has been directly linked to the presence of dipolar groups 18,22 and their spontaneous polarization in the vicinity of a metal surface. 21,23 Herein, we introduce an approach to improve performance of organic photovoltaic devices that relies on using the amine-functionalized fullerene derivative, 2,3,4-tris(3-(dimethylamino)propoxy)fulleropyrrolidine (C 60 -N), 18 as an additive in a BHJ active layer to modify the electronic structure of the device.…”