Synthesis and Characterization of Squaraine‐Based Conjugated Polymers With Phenylene Linkers for Bulk Heterojunction Solar Cells

Abstract

Abstractπ‐Conjugated copolymers consisting of squaraine dyes as light‐harvesting components and phenylene linkers (PSQ) are presented. They show intense absorption in visible (Vis) and near‐infrared (NIR) region, originating with the intramolecular charge transfer of the dye. Although their optical and electrochemical properties are dominantly derived from dye components, phenylene linkers affect aggregation in the solid state and phase segregation of the PSQ/PCBM composites. Bulk heterojunction solar cells consisting of PSQ/PCBM exhibit spectral response in Vis–NIR region, and they show power conversion efficiencies up to 0.64%. The copolymer approach to develop squaraine‐based polymers enables the auxiliary tuning of the physical properties that determine photovoltaic performance through the choice of linkers.

Synthesis, electrochemical, and optical properties of low band gap homo- and copolymers based on squaraine dyes

“…In the field of indolenine‐squaraines, only few approaches have been reported on the synthesis of donor‐bridged squaraine copolymers. In search of polymers with broad absorption in the NIR region, Maeda et al used both meta ‐ and para ‐linked phenylene bridges but the bathochromic shift of the absorption was very small . A similar behavior was observed by Kuster and Geiger where various bridges between indolenine‐squaraines were investigated.…”

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.…”

“…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.…”

Squaraine‐Based Polymers: Toward Optimized Structures for Optoelectronic Devices

“…The organic photovoltaic (OPV) device incorporating indolenine‐based polysquaraine Psq1 /PC 61 BM (1:1) active blend film yielded a power conversion efficiency (PCE) of 0.45% ( V oc = 0.48 V, J SC = 2.82 mA cm −2 , fill factor (FF) = 34%) (Figure ). More recently, Nakazumi and co‐workers developed 1,3‐squaraine‐based polymers with phenylene linkers, Psq2 (Figure ), and showed that Psq2 /PC 61 BM bulk heterojunction (BHJ) devices exhibited power conversion efficiencies values of up to 0.64% ( V oc = 0.47 V, J SC = 4.6 mA cm −2 , FF = 29%) . Finally, Yang et al focused their attention on 1,2‐squaraine moiety rather than the well‐known isomeric 1,3‐squaraine counterpart as the A‐unit of D–A conjugated polymers ( Psq3 and Psq4 , Figure ).…”