Synthesis and Characterization of CdTe Tetrapods by Continuous Precursor Injection Method

Abstract

CdTe tetrapods have been got a considerable attention as appropriate solar energy harvesting material due to their good exciton separation at the surface and transport along the branches, and suitable absorption range covering near IR region. For the realization of efficient solar cells, it is essential to produce CdTe tetrapod with uniform morphology in a large quantity: CdTe tetrapods with arms as long as possible for the efficient electron conduction and well-controlled arm diameter for the maximum solar energy absorption. In order to achieve these objectives, we have carried the controllable and scalable synthesis of CdTe tetrapods in terms of kinetic parameters. Using our newly developed continuous precursor injection (CPI) method- the approach involves the successive and slow injection of precursors at a well-controlled rate so that the reaction condition remains in the kinetic growth regime for the anisotropic growth, we were able to produce CdTe tetrapods with well-controlled arm length and diameter and appropriate solar energy absorption. To be specific, CdTe tetrapods with an arm length from 20 to 70 nm and arm diameter from 3 to 12 nm were produced and they showed high structural selectivity of 76 %. In order to synthesize CdTe tetrapods with high uniformity, the nucleation step and the growth (i.e., seeded growth method) step should be separately carried out. First CdTe tetarapod seeds were synthesized. And then, secondly the slow growth with stabilized seeds obtained from the nucleation step was preceded by the continuous precursor injection (CPI). To maintain the anisotropic growth to proceed longer, it was necessary to keep the precursor concentration supplied by CPI in the kinetic growth regime. It is required to clearly understand how to find proper precursor injection rate and reaction temperature to generate CdTe tetrapod with desired arm length and diameter. We need to do more work on the growth mechanism and to figure out how to control the reactivity of precursors or to develop new precursors in order to generate the desired CdTe tetrapods with hugely uniform morphology and crystallinity.