CdTe1−xSx (x ⩽ 0.05) thin films synthesized by aqueous solution deposition and annealing

Abstract

While CdS thin films are commonly deposited from aqueous solutions, CdTe thin films are extremely difficult to deposit directly from aqueous solution. In this work, we report on polycrystalline CdTe1−xSx thin films synthesized via deposition from aqueous precursor solutions followed by annealing treatments and on their physical properties. The deposition method uses spin-coating of alternating Cd2+ and Te2− aqueous solutions and rinse steps to allow formation of the films but to shear off excess reactants and poorly-bonded solids. Films are then annealed in the presence of CdCl2 as is commonly done for CdTe photovoltaic absorber layers deposited by any means. Scanning electron microscopy (SEM) reveals low void fractions and grain sizes up to 4 µm and x-ray diffraction (XRD) shows that the films are primarily cubic CdTe1−xSx (x ⩽ 0.05) with random crystallographic orientation. Optical transmission yields bandgap absorption consistent with a CdTe1−xSx dilute alloy and low-temperature photoluminescence (PL) consists of an emission band centered at 1.35 eV consistent with donor–acceptor pair (DAP) transitions in CdTe1−xSx. Together, the crystalline quality and PL yield from films produced by this method represent an important step towards electroless, ligand-free solution processed CdTe and related alloy thin films suitable for optoelectronic device applications such as thin film heterojunction or nanodipole-based photovoltaics.