Synthesis of type II CdTe-CdSe nanocrystal heterostructured multiple-branched rods and their photovoltaic applications

Novel type II CdTe-CdSe semiconductor nanocrystal heterostructures (SNCHs) with multiple-branched rod morphology were synthesized by epitaxial growth of CdSe from CdTe nanocrystals in solution, and the SNCHs were characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), energydispersive spectrometry (EDS), and X-ray diffraction (XRD) analysis. The SNCHs are composed of a CdTe core and CdSe branches, and most of the heterostructured nanocrystals have about 10 branched rods with thickness of 3-5 nm and length of 10-30 nm. The absorption spectra of the SNCHs covered the whole visible region from 380 to 780 nm with a distinct peak at 560~580 nm corresponding to the absorption of CdSe nanocrystals. The quenching of the photoluminescence (PL) peak of the CdTe core was observed in the SNCHs, which indicates that photoinduced charge separation existed in the SNCHs. Furthermore, the photovoltaic properties of the SNCHs were studied on the basis of the devices with single component of the SNCHs and with the blend of P3HT and the SNCHs. The device based on the SNCHs single component showed an open-circuit voltage (V_oc) of 0.40 V, a short-circuit current density (J _Sc) of 0.018 mA/cm², fill factor (FF) of 38%, and power convention efficiency (η) of 0.003% under the illumination of AM1.5, 100 mW/cm², which is greatly improved in comparison with that of the homostructured semiconductor nanocrystals. For the hybrid P3HT/SNCHs device, the J_sc, V_oc, FF, and η of the device reached 0.58 mA/cm², 0.63V, 43%, and 0.16% respectively.