CdS–CdTe Solar Cell Prepared by Vapor Phase Epitaxy

Abstract

CdS–CdTe solar cells were prepared by epitaxial growth of CdS on p·CdTe wafers, and properties of the cells were extensively studied. The cells have a junction structure of n·CdS–(n or i)·CdTe–p·CdTe. Formation of the (n or i) layer is due to diffusion of In into CdTe; the thickness of the layer was 0.5 µm in the most efficient cell. The best cell exhibited a solar conversion efficiency of 10.5% under illumination by sunlight (AM1.3, 68 mW/cm2), and 6.0% under illumination by a simulated sunlight (AMO). The high efficiency is attributed to the reduction in both the series resistance and surface recombination, which results from the presence of the heavily doped CdS layer on the wafer. The cell is not humidity sensitive and is stable in the forward bias test, These results suggest strongly that practically useful solar cells can be manufactured from this type of junction.

Development of high-efficiency, thin-film CdTe solar cells. Final subcontract report, 1 February 1992--30 November 1995

“…In addition, rapid thermal processing lowers energy consumption and can speed cell fabrication. RTP has been used for homojunction formation in the CdTe, I&, and CuInSe, thin film solar cells [3,4], as well as for grain growth in the amorphous/polycrystalline silicon cells [5,6]. However, no research has been conducted on the CdTe/CdS heterojunction cells using RTP.…”

“…This section reviews the device physics pertaining to homojunction and heterojunction solar cells [1,2,3]. It is well known that without external voltage or light bias applied to a p-n junction, the diffusion and drift current within the junction are balanced and there is no net current flow.…”

“…Other factors, such as substrate orientation, total flow rate, and chamber geometry also determine the growth process. [3][4][5] where R and R' are the organic radicals, M is a group I1 or 111 metal, and X is a group V or VI element. The vapor reactants %M and G X are thermally decomposed at elevated temperatures to form the nonvolatile product MX, which is deposited on the substrate and the volatile products RH and R'H are flushed by the H2 gas into the exhaust.…”

“…There has been a steady increase in the efficiency of these cells in the past few years, with the maximum reported efficiency of 15.8% to date [3]. In order to achieve high efficiencies reproducibly and approach the estimated potential efficiency of 2 18%, much more basic research on defects, loss mechanisms, and process optimization is required.…”

Spectroscopic studies ofCdTe(111)bulk and surface electronic structure

“…It is widely used in various devices including γ-and x-ray spectrometers, solar cells, optoelectronic and optoacoustic modulators, and infrared windows [1][2][3][4][5]. It serves as an excellent substrate for epitaxial growth of other II-VI compounds such as Hg x Cd 1-x Te with a tunable band gap [6][7][8], and as a key parent material for the realization of the quantum spin Hall phase [9][10][11].…”