5-Alkyloxy-6-fluorobenzo[c][1,2,5]thiadiazole- and Silafluorene-Based D–A Alternating Conjugated Polymers: Synthesis and Application in Polymer Photovoltaic Cells

Abstract

Three donor–acceptor (D–A) alternating conjugated polymers with silafluorene as the donor unit, 5-alkyloxy-6-fluorobenzothiadiazole as the acceptor unit, and thiophene as the spacer has been synthesized and used as donor materials for polymer solar cells (PSCs). The introduction of a fluorine atom on the benzothiadiazole unit can lower the HOMO and LUMO energy level of the resulted polymers to afford higher open circuit voltage (V oc); whereas the introduction of a flexible alkyloxy chain on benzothiadiazole unit can increase the solubility of the resulted polymers without interfering the close packing of polymer chains in the solid state. High molecular weight polymers P-1a, P-1b, and P-1c, which are fully soluble in 1,2-dichorobenzene (DCB) at elevated temperature, have been prepared by Suzuki polycondensation. Among these polymers, P-1c exhibited the highest hole mobility up to 1.36 × 10–2 cm2 V–1 s–1. PSCs based P-1b:PC71BM demonstrated the highest V oc up to 0.98 V. P-1a:PC71BM based PSCs gave the highest power conversion efficiency (PCE) of 6.41%, which is the highest value among solar cells with benzothiadiazole- and silafluorene-containing polymers as the donor material.

Effect of substitution positions of alkyl side chains in phenanthrodithiophene–isoindigo copolymers: The enhancement of crystallinity and control of molecular orders

“…For instance, conformation of the polymer backbone and curvature that strongly depends on the π ‐conjugation length, regularity, symmetry, and coplanarity of a repeating unit drastically, can often impact on the polymer packing structure in the solid state . In addition, the incorporation of side chains onto the polymer backbone with various factors such as substitution position, the number, topology, length, branching position, and attachment density, can facilitate the ideal molecular arrangements and high‐crystalline structures in both neat and blended films with an n‐type material, resulting in high OFET and OPV characteristics. Along this line, although many researchers have investigated the side chain engineering of various semiconducting polymers in numerous combination of donor and acceptor units to maximize the device performances, the prediction of appropriate side chains in each polymer is still difficult.…”

Synthesis of di(ethylene glycol)-functionalized diketopyrrolopyrrole derivative-based side chain-conjugated polymers for bulk heterojunction solar cells

“…[14][15][16] PSCs providing good PV performance have been studied widely in which the conjugated polymers contain p-type electron-donating groups and electron-donating and -withdrawing donor-acceptor (D-A)-type structures. 10,12,17 The bipolar characteristics of conjugated polymers containing electron-and hole-transporting moieties are responsible for the lower-energy band gaps and higher charge mobilities of the photoactive layers that can enhance the PV efficiencies of PSCs. In addition, polythiophene (PT) derivatives bearing electron-donating and -withdrawing pendant groups, so-called two-dimensional low band gap conjugated polymers, have been proposed by several groups for PSC applications.…”

Insights into the influence of fluorination positions on polymer donor materials on photovoltaic performance

“…[19][20][21][22][23] The absorption, energy level and charge mobility of polymers and even the morphology of blend films can be modulated by polymer structure engineering. [24][25][26][27][28][29] The design of polymers with a donor (D)-acceptor (A) alternating structure is an effective way to broaden their absorption. [30][31][32][33] The introduction of fluorine atoms onto either donor unit or acceptor unit of the polymers can enhance the crystallization of polymers and decrease their energy levels, [34][35][36][37][38][39] due to its strong electron-withdrawing nature and the ability of forming noncovalent bond between fluorine and hydrogen or sulfur atom (F···H or F···S).…”