Dye‐Containing Polymers with π‐Extened Diketopyrropyrrole Derivatives for Semi‐Transparent Organic Photovoltaics

Abstract

Dye‐containing polymers P1 (PEDPP‐OT‐BDT) and P2 (PEDPP‐OT‐BDTT) including a π‐extended diketopyropyrrole (DPP) derivative and electron‐rich thiophene fused ring units (4,8‐bis((2‐ethylhexyl)oxy)benzo[1,2‐b:4,5‐b']dithiophene for P1 and 4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b']dithiophene for P2) were synthesized as narrow band gap dyes. A π‐extended DPP (EDPP‐OT‐BrPh), fragment of the polymers P1 and P2, was obtained by extending the π‐conjugation of DPP using Ru(III)‐catalyzed C‐H and N‐H activation reported by Gońka et al. in 2019, exhibiting a high quantum yield (φem = 0.84) and small HOMO‐LUMO gap (Eg = 1.69 eV) due to the spatial overlap of the HOMO and LUMO orbitals. The solubility of the π‐extended DPP was improved by introducing four 2‐octylthophene side chains around the periphery of the planer dye moiety, while maintaining the high planarity of the dye molecule, which is essential to the function of optoelectronic devices. As a result, P1 and P2, polymerized with the π‐extended DPP and BDT derivatives, exhibit carrier mobility of approximately 10‐5 cm2/Vs in organic field‐effect transistors (OFETs). In bulk heterojunction (BHJ) solar cells with [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM), they demonstrate a power conversion efficiency (PCE) of 1.0% with an average transmittance (AVTs) of around 60%.