Raman spectroscopy and photoluminescence (PL) were used to investigate the improved short-circuit current density (JSC) of CdS/CdSe quantum dot (QD)-sensitized solar cells with multi-walled carbon nanotubes (MWCNTs). Raman and PL experiments were carried out in order to explore the hot-electron and cold-electron injections, respectively. The experimental results showed that the concentration of MWCNTs influences the hot-electron and cold-electron injections from CdS/CdSe QDs to TiO2 nanoparticles. Therefore, the improved JSC in CdS/CdSe QD-sensitized solar cells can be explained as due to the better electron injections.