Quantum Dot Solar Cells. Tuning Photoresponse through Size and Shape Control of CdSe−TiO₂ Architecture

TLDR

The study aims to tune the photoelectrochemical response and photoconversion efficiency of CdSe–TiO₂ solar cells by controlling quantum‑dot size and exploiting TiO₂ nanotube architecture, while outlining future improvements via a rainbow‑cell design. Size‑variant CdSe quantum dots were assembled onto TiO₂ particle and nanotube films using a bifunctional linker, enabling electron injection into TiO₂ upon band‑gap excitation to generate photocurrent in a photoelectrochemical cell. The authors demonstrated that smaller CdSe dots and TiO₂ nanotube morphology raise the IPCE to 45 % and the power‑conversion efficiency to ≤1 %, confirming that size control and nanotube architecture enhance charge transport and overall performance.

Abstract

Different-sized CdSe quantum dots have been assembled on TiO2 films composed of particle and nanotube morphologies using a bifunctional linker molecule. Upon band-gap excitation, CdSe quantum dots inject electrons into TiO2 nanoparticles and nanotubes, thus enabling the generation of photocurrent in a photoelectrochemical solar cell. The results presented in this study highlight two major findings: (i) ability to tune the photoelectrochemical response and photoconversion efficiency via size control of CdSe quantum dots and (ii) improvement in the photoconversion efficiency by facilitating the charge transport through TiO2 nanotube architecture. The maximum IPCE (photon-to-charge carrier generation efficiency) obtained with 3 nm diameter CdSe nanoparticles was 35% for particulate TiO2 and 45% for tubular TiO2 morphology. The maximum IPCE observed at the excitonic band increases with decreasing particle size, whereas the shift in the conduction band to more negative potentials increases the driving force and favors fast electron injection. The maximum power-conversion efficiency ≤1% obtained with CdSe−TiO2 nanotube film highlights the usefulness of tubular morphology in facilitating charge transport in nanostructure-based solar cells. Ways to further improve power-conversion efficiency and maximize light-harvesting capability through the construction of a rainbow solar cell are discussed.