Magnetron sputtering for II-VI solar cells: thinning the CdTe

Abstract

Magnetron sputtering (MS) of CdTe and related II-VI materials facilitates low energy ion and electron bombardment that promotes good film growth at substrate temperatures well below those needed for other physical vapor deposition methods. MS also provides good control of deposition rates while allowing scale-up to large areas. In this paper we review the use of MS for deposition of polycrystalline thin films of CdS, CdTe and related materials for solar cells with a focus on reducing the thickness. We relate the deposition conditions and plasma properties determined by Langmuir probe measurements to some of the materials properties of the films through spectroscopic ellipsometry and high resolution electron microscopy. For cells with CdTe layers from 0.35 to 2.5 μm, we have done a first-order optimization of chloride treatment conditions and back contact structure. We discuss the influence of CdTe thickness and post-deposition processing on the efficiency, open-circuit voltage, short-circuit current, and fill factor and show that 10% efficient cells can be fabricated with 0.5 μm of CdTe.