Polymeric Squaraine Dyes as Electron Donors in Bulk Heterojunction Solar Cells

TL;DR

This study synthesizes a polysquaraine polymer with low band gap properties, demonstrating its potential as an electron donor in bulk heterojunction solar cells with a maximum efficiency of 0.45%.

Contribution

It introduces a new polysquaraine polymer synthesized via Yamamoto coupling and evaluates its electronic and photovoltaic properties in solar cells.

Findings

Polymer shows broad absorption from 300 to 850 nm.

Power conversion efficiency reaches 0.45%.

External quantum efficiency indicates promising photoresponse.

Abstract

A polysquaraine low band gap polymer was synthesized by Yamamoto coupling of a monomeric dibromo indolenine squaraine dye. The resulting polymer has a weight average molar mass in the order of Mw ~30.000-50.000 and a polydispersity of ca. 1.7 as determined by gel-permeation chromatography (GPC). The electronic properties of monomer and polymer were investigated by cyclic voltammetry, absorption and emission spectroscopy. Owing to exciton coupling the absorption bands of the polymer are red-shifted and strongly broadened compared to the monomer squaraine dye. Bulk heterojunction solar cells were prepared from blends of the polysquaraine with the fullerene derivative [6,6]-phenyl C61-butyric acid methyl ester (PCBM) in different weight ratios (1:3 to 1:1). The power conversion efficiencies under simulated AM 1.5 conditions yielded 0.45 % for these non-optimized systems. The external quantum efficiency (EQE) shows that the photoresponse spans the range from 300 to 850 nm, which illustrates the promising properties of this novel organic semiconductor as a low band gap donor material in organic photovoltaics.