Tailoring Light‐Harvesting in Zn‐Porphyrin and Carbon Fullerene based Donor‐Acceptor Complex through Ethynyl‐Extended Donor π‐Conjugation

Abstract

AbstractOrganic photovoltaic efficiency though currently limited for practical applications, can be improved by means of various molecular‐level modifications. Herein the role of extended donor ‐conjugation through ethynyl‐bridged meso‐phenyl/pyridyl on the photoinduced charge‐transfer kinetics is studied in noncovalently bound Zn‐Porphyrin and carbon‐fullerene based donor‐acceptor complex using time‐dependent optimally tuned range‐separated hybrid combined with the kinetic rate theory in polar solvent. Noncovalent dispersive interaction is identified to primarily govern the complex stability. Ethynyl‐extended ‐conjugation results in red‐shifted donor‐localized Q‐band with substantially increased dipole oscillator strength and smaller exciton binding energy, suggesting greater light‐harvesting efficiency. However, the low‐lying charge‐transfer state below to the Q‐band is relatively less affected by the ethynyl‐extended ‐conjugation, yielding reduced driving forces for the charge‐transfer. Detailed kinetics analysis reveals similar order of charge‐transfer rate constants (~1012 s−1) for all donor‐acceptor composites studied. Importantly, enhanced light‐absorption, smaller exciton binding energy and similar charge‐transfer rates together with reduced charge‐recombination make these complexes suitable for efficient photoinduced charge‐separation. These findings will be helpful to molecularly design the advanced organic donor‐acceptor blends for energy efficient photovoltaic applications.