Characterization of a hollow cathode styled plasma reactor for photovoltaic applications

Abstract

Heated pocket deposition sources are often used for the rapid manufacture of thin film CdS/CdTe photovoltaic devices, however, new process methods are needed to further improve the quality of the films, increase cell efficiency, and reduce production costs. A plasma-enhanced, close-spacing sublimation (PECSS) technique utilizing a hollow cathode style discharge in a heated pocket has recently been developed as a candidate process method. It has been successfully used to eliminate pin holes, to dope CdS with oxygen, and dope CdTe absorption layers; all of which have resulted in higher device efficiencies. This work presents a characterization of plasma properties inside the hollow cathode style reactor including: plasma density, electron temperature, and plasma potential. Additionally, the uniformity of the ion current flux to the substrate is presented for nitrogen/oxygen and argon feed gases by means of in situ surface probes fabricated by segmenting a transparent conductive oxide film on a glass substrate. A three-dimensional model was developed and used to calculate plasma production and transport processes, and to gain an understanding of the relative roles of energetic primaries and bulk cold electrons on spatial ionization rates that develop within the reactor plasma as a function of gas pressure and geometry. Comparisons between the model and experimental measurements are presented and good agreement has been observed when the appropriate spatially varying ionization rates are estimated.

Characterization of Atmospheric Electrical Discharge in Pin-water Configuration at Different NaCl Concentrations

“…The electron temperature (T e )(in eV) was one of the most important variables used for evaluating plasma properties. It calculated by the Boltzmann plot method as follows [23,24]:…”

“…The full width at half maximum (FWHM) and lorentzian fitting were used for determining the electron number density. ( ) (in cm -3 ) with the variation of NaCl concentrations using stark broadening of (N 2 I) for the following wavelengths (337.13, 357.69 and 380.49)(nm)) that is collected through the following relation [24,26]:…”

“…The electron Debye length (λ D ) (in m) was defined as a microscopic maximum spatial scale for the charge-separation which represents the shielding distance or the thickness of the plasma sheath which is calculated as [24,26,27]:…”

2D Fluid Modeling of Light Pumped Na Containing Plasma to Develop a Prototype of a Photo Electromotive Force Converter

“…Such gas-plasma photoelectric converters have not been extensively researched yet. Although plasma is used in numerous applications to enhance photovoltaic efficiency [5,6], in plasma itself, the photovoltaic effect has received little attention. For example, such, when the increase in temperature does not reduce the efficiency, but, on the contrary, increases the conversion efficiency unlike semiconductor solar panels [7].…”

Development of plasma enhanced closed space sublimation for the deposition of CdS:O in CdTe solar cells

“…These innovations must be scalable to large area and consume as little time as possible. With the recent successful development of plasma cleaner hardware [1,2,3] and the proven scalability of inline close space sublimation (CSS), the next research thrust was to incorporate plasma enhanced techniques into other stages of the in-line CdTe manufacturing process. To do this a hollow cathode plasma cleaner-like discharge was incorporated within a CSS source to allow the sublimating material and the film growth surface to be modified during deposition.…”