Enhanced transient photovoltaic characteristics of core-shell ZnSe/ZnS/L-Cys quantum-dot-sensitized TiO2 thin-film

摘要

Photoanodic properties greatly determine the overall performance of quantum-dot-sensitized solar cells (QDSCs).In the present report,the microdynamic behaviors of carriers in the nanocomposite thin-film,a ZnSe QD-sensitized mesoporous La-doped nano-TiO2 thin-film,as a potential candidate for photoanode,are probed via nanosecond transient photovoltaic (TPV) spectroscopy.The results confirm that the L-Cys ligand has a dual function serving as a stabilizer and molecular linker.Large quantities of interface states are located at the energy level with a photoelectric threshold of 1.58 eV and a quantum well (QW) depth of 0.67 eV.This QW depth is approximately 0.14 eV deeper than the depth of QW buried in the ZnSe QDs,and a deeper QW results in a higher quantum confinement energy.A strong quantum confinement effect of the interface state may be responsible for the excellent TPV characteristics of the photoanode.For example,the peak intensity of the TPV response of the QD-sensitized thin-film lasts a long time,from 9.40 × 10-7 s to 2.96 × 10-4 s,and the end time of the PTV response of the QD-sensitized thin-film is extended by approximately an order of magnitude compared with those of the TiO2 substrate and the QDs.The TPV characteristics of the QD-sensitized thin-film change from p-type to n-type for the QDs before and after sensitizing.These properties strongly depend on the extended diffusion length of the photogenerated carries and the reduced recombination rate of photogenerated electron-hole pairs,resulting in prolonged carrier lifetime and an increased level of electron injection into the TiO2thin-film substrate.