Amplification of Solar Energy Conversion in Quantum‐Confined CdSe‐Sensitized TiO2 Photonic Crystals by Trapping Light

Abstract

Photonic effects amplifying solar energy conversion are reported in titania inverse opals sensitized with quantum‐confined CdSe films. TiO2 inverse opals (i‐TiO2‐o) and unstructured nanocrystalline TiO2 (nc‐TiO2) films are sensitized with CdSe deposited via successive ionic layer adsorption and reaction (SILAR) by generating Se2− in situ under inert atmosphere, and the film absorbance is tuned by the number of SILAR cycles. Photonic effects are investigated while varying the i‐TiO2‐o stop band position relative to CdSe films’ absorbance. i‐TiO2‐o films with stop band at 700 and 560 nm are sensitized with CdSe having absorption edges at 600 and 650 nm thus tuning absorbance to the red and the blue of the stop band. Significant amplification in photon‐to‐current conversion efficiency is measured when CdSe films prepared via two cycles are adsorbed on i‐TiO2‐o with a stop band at 700 nm, with a maximum average enhancement factor equal to 6.7 ± 1.6 at 640 nm, 60 nm to the blue of the stop band center, relative to nc‐TiO2 sensitized with comparable CdSe amounts. The gain is observed over a wide frequency range to the blue of the stop band and is greatest when film absorbance was low. The photocurrent gain is not a result of differences in the rates of charge separation or charge transport, and occurs in the same frequency range where absorbance amplification is measured to the blue of the 700‐i‐TiO2‐o stop band, and is thus attributed to slow light effects enhancing absorbance in the photonic crystal environment.