Modulating FRET in Organic−Inorganic Nanohybrids for Light Harvesting Applications

Abstract

The energy transfer efficiencies of organic−inorganic nanohybrids comprised of two structurally similar squaraine dyes and CdSe nanoparticles were studied in detail and compared. Carbazole based unsymmetrical squaraine dyes (CTSQ-1 and CTSQ-2) having modified absorption characteristics were considered for modulating the effect of the overlap integral on energy transfer rate with the designed QDs. CTSQ- 2 with ∼1.75 times higher molar extinction coefficient and 35 nm red-shift in absorption resulted in an ∼2.4 times faster energy transfer rate with QD. The calculated energy transfer rates (kT = 1.35 × 108 s−1 and 3.26 × 108 s−1 respectively for QD:CTSQ-1 and QD:CTSQ-2 nanohybrids) are at least one order of magnitude higher than both radiative (kr = 5.97 × 106 s−1) and nonradiative decay rate constants (knr = 1.89 × 107 s−1) of QDs yielding very high FRET efficiency. The Stern−Volmer analysis of the quenching data indicated mainly static interaction of dyes with the QDs thus suggesting formation of organic−inorganic nanohybrids. When incorporated in dye-sensitized solar cells, the nanohybrids with 93% FRET efficiency, exhibited an overall 43% improvement in the photovoltaic performance. Among the two architectures employed for device fabrication the one with the smallest donor−acceptor distance delivered the best performance. Due to increased contribution from QDs, the IPCE spectra clearly indicate panchromatic response from the visible to NIR region. Thus, photovoltaic performance of NIR absorbing dyes were successfully improved by constructing panchromatic organic−inorganic nanohybrid materials.