Reduced charge recombination in a co-sensitized quantum dot solar cell with two different sizes of CdSequantum dot

Abstract

An efficient photoelectrode is fabricated by sequentially assembling 2.5 nm and 3.5 nm CdSe quantum dots (QDs) onto a TiO₂ film. As revealed by UV-vis absorption spectroscopy, two sizes of CdSe QD can be effectively adsorbed on the TiO₂ film. With a broader light absorption range and better coverage of CdSe QDs on the TiO₂ film, a power conversion efficiency of 1.26% has been achieved for the TiO₂/CdSe QD (2.5 nm)/CdSe QD (3.5 nm) cell under the illumination of one Sun (AM 1.5G, 100 mW cm⁻²). Electrochemical impedance spectroscopy shows that the electron lifetime for the device based on TiO₂/CdSe QD (2.5 nm)/CdSe QD (3.5 nm) is longer than that for devices based on TiO₂/CdSe QD (2.5 nm) and TiO₂/CdSe QD (3.5 nm), indicating that the charge recombination at the interface is reduced by sensitizing with two kinds of CdSe QDs.