A comparative study of diketopyrrolopyrrole and isoindigo based polymers for organic photovoltaic applications

• The polymers based on diketopyrrolopyrrole and isoindigo were studied and compared.
• The polymer based on diketopyrrolopyrrole showed absorption extended into near IR region.
• The polymer based on isoindigo showed little absorption in near IR region.
• The isoindigo based polymer showed lower HOMO/LUMO energy than DPP based polymer.

Two new donor/acceptor π-conjugated polymers with functional dyes, either diketopyrrolopyrrole or isoindigo as the electron accepting units and 5,10-bis(2,3-didecylthiophen-5-yl)-naphtho[1,2-b:5,6-b′]difuran as an electron donating units have been synthesized. The photo-physical, electrochemical and photovoltaic properties of the new polymers have been studied and compared. With the same donor unit, the diketopyrrolopyrrole based polymer showed low bandgap and broad absorption extended into near IR region. The isoindigo based polymer showed little absorption in near IR region. However, the isoindigo based polymer showed more efficient absorption than diketopyrrolopyrrole based polymer in the most of visible region (from 300 to 690 nm) in solution. The isoindigo based polymer showed lower HOMO and LUMO energy levels than diketopyrrolopyrrole based polymer. The isoindigo polymer based solar cell devices consistently showed higher open circuit voltages than the diketopyrrolopyrrole polymer based devices.

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