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.

Transition metal nitride contacts for CdTe photovoltaics

“…Following deposition of the junction, the layers were treated with CdCI2 at 387°C for 30 minutes in dry air. The device processing has been described in detail previously [15].…”

Nitrogen doped chalcopyrites as contacts to CdTe photovoltaics

“…[5] These substrates consist of soda-lime glass coated with a four layer stack; from the substrate to the ambient these layers include SnO 2 , SiO 2 , SnO 2 :F, and the HRT. This results in an ~15 Ω/square transparent front contact.…”

“…Cu is diffused into the back contact region by an optimized annealing process for 45 min at 150°C in laboratory ambient. [5] On selected 5 cm x 5 cm pieces of the substrates a Br 2 /methanol etch was performed to remove the oxide and form a Te rich near-surface (top ~ 1 nm) of the CdTe back surface prior to the back contact deposition.…”

“…The resulting baseline devices were 12.2±0.2% efficient with excellent uniformity across the substrates. A detailed description of the devices and processing may be found in Reference [5].…”

Characterizing thin film PV devices with Low-Incidence Surface Milling by Focused Ion Beam

“…CdS/CdTe thin films investigated in this work were deposited by RF magnetron sputtering in two different sputtering geometries, normal incidence (our "Classic" system) in which the deposition occurs with the substrate facing the sputter targets [1,2] and angle incidence (AJA system) in which the deposition occurs at about 45° to a rotating substrate. The substrate temperature during deposition was approximately 250°C with an RF power density of 1 W/cm 2 in the Classic, and 270°C with 2.5 W/cm 2 in the AJA.…”