Cooperatively Tuning Phase Size and Absorption of Near IR Photons in P3HT:Perylene Diimide Solar Cells by Bay-Modifications on the Acceptor

Abstract

P3HT is a widely used and commercial polymer donor, but it cannot absorb near IR solar photons. Chemical accessibility to tune the frontier molecular orbits of π-conjugated small molecule acceptors increases the possibility to improve their near IR absorption, which is complementary to P3HT. Taking the aggregation tendency of the planar π-system into account, we herein use the traditional n-type organic semiconductor of perylene diimide (PDI) as the model backbone, showing a molecular way to cooperatively tune the aggregation tendency and absorption of the near IR photons. Practically, we replace the 2-methoxylethoxyl units from the mother PDI monomer (O-PDI-O), one-by-one, with the 4,8-bis(2-(2-ethylhexylthienyl) benzo[1,2-b′:4,5-b′]dithiophene (BDT) moieties, giving two other PDI monomers of B-PDI-O and B-PDI-B. Because of the photoinduced intramolecular charge transfer transition from the BDT unit to the PDI core, B-PDI-B exhibits a broad absorption shoulder beyond 600 nm in the dilute solution, and be...