Photonic crystals have attracted interest for enhancing light energy conversion in nanostructures because of the possibility of trapping light in these architectures. Type-II quantum dots, such as Q-CdTe/CdSe, offer advantages of enhanced charge separation and absorbance of light energy smaller than the energy gap of the core and shell materials. In this work, we investigated light energy conversion at titania inverse opals (i-TiO2-o) sensitized with Q-CdTe whose surface was modified with selenide, before and after annealing, and compared to similarly sensitized nc-TiO2. The effects of selenide modification and of the inverse opal structure were interrogated. i-TiO2-o films with stop-band at ca. 540-570 nm were sensitized with Q-CdTe of three sizes in the range 2-4 nm with absorbance edges to the red, within, and to the blue of the stop band. A significant increase in the light-to-current conversion was measured after Se2- modified Q-CdTe on i-TiO2-o and nc-TiO2 films were annealed, attributed to a better interface with type-II Q-CdTe/CdSe. Enhanced absorbance and quenching of emission confirmed Q-CdTe/CdSe properties. A significant gain was measured at green-emitting 2.3 nm Q-CdTe on i-TiO2-o relative to nc-TiO2, with an average enhancement factor of ca. 4-fold to the blue and the red of the stop band. A smaller gain was measured for larger ca. 3 nm Q-CdTe particles. Absorbance spectra of sensitized inverse opals showed peaks to both the blue and red edge of the stop band, indicating amplified absorbance at these frequencies. A significant increase, between 4- and 5-fold on average, in the overall incident photon-to-current-conversion efficiency at 400-700 nm resulted at green-Q-CdTe/CdSe/i-TiO2-o relative to Q-CdTe/nc-TiO2, in part due to the type-II quantum dots and in part to light trapping in the inverse opal. Studies are ongoing on the role of disorder in light trapping in real photonic crystals.

Amplified light energy conversion at TiO2 photonic crystals sensitized with Q-CdTe modified with selenide: Effects of light trapping and selenide treatment

256th National Meeting (2018)

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