Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Patent
1998-04-06
1999-06-29
Chapman, Mark
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
438 85, 438 89, 438 97, H01L 21477
Patent
active
059163755
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photovoltaic cell for converting solarlight energy into electrical energy and, more particularly, a manufacturing method to enhance conversion efficiency of a photoelectric conversion device such as a thin film photovoltaic cell, which employs a CdTe thin film formed on a transparent substrate such as a glass substrate as a light absorber layer.
2. Description of the Prior Art
It has been well known that CdTe has a high absorption coefficient of more than 10.sup.4 cm.sup.-1 and its thin film of about 5 .mu.m thickness is capable of sufficiently absorbing the solarlight. The CdTe thin film is promising as material for the thin film photovoltaic cell since it is easy to form a polycrystal film of high quality by virtue of various thin film forming methods such as a printing method, a plating method, an evaporation method, etc. In addition, a band gap of CdTe (.about.1.47 eV) is most suitable for solarlight spectrum amongst various materials for the photovoltaic cell, and thus the highest conversion efficiency can be expected. It has also been calculated that theoretical efficiency of a CdTe thin film photovoltaic cell is in excess of 20%. However, the highest value of the conversion efficiency of the CdTe thin film photovoltaic cell which has been reported up to now is about 15%, which is largely different from a theoretical value. Like the above, the photovoltaic cell employing the CdTe thin film as the light absorber layer has been expected as the low cost and high efficiency photovoltaic cell, but it is difficult under the existing circumstances to manufacture the photovoltaic cell which employs the CdTe thin film having sufficiently high conversion efficiency as the light absorber layer with good reproducibility.
As the photovoltaic cell employing the CdTe thin film as the light absorber layer in the prior art, a pn junction photovoltaic cell is common which is formed by depositing a p-type CdTe layer 4 on an n-type CdS layer 3, as shown in FIG. 1. Though illustrated upside down in FIG. 1, a transparent conductive film 2 such as an indium-tin oxide film (ITO film) is formed on a glass substrate 1, then the n-type CdS layer 3 is formed 0.1 to 10 .mu.m thick thereon, then the p-type CdTe layer 4 is formed 1 to 10 .mu.m thick thereon, and then an ohmic electrode 5 made of Cu/Au, etc. is formed thereon. If a sheet resistance of the CdS layer 3 is sufficiently small, the transparent conductive film 2 may be omitted.
In the prior art, the CdTe/CdS photovoltaic cell shown in FIG. 1 has been manufactured according to manufacturing steps described in the following. That is, the cell has been manufactured according to following steps (1) to (5) (this is called "a first manufacturing method in the prior art" hereinafter):
(1) The transparent conductive film 2 such as the indium-tin oxide (ITO) is deposited by the sputtering method, etc. on the glass substrate 1 such as a Corning 7059 substrate to have a thickness of about 150 nm to 1 .mu.m such that a sheet resistance of less than 10 .OMEGA./.quadrature. can be given.
(2) The n-type CdS layer 3 is deposited by the vacuum evaporation method, etc. at a substrate temperature 350.degree. C. to have a thickness of 0.1 to 10 .mu.m. If a sheet resistance of the CdS layer 3 is enoughly small, there is no necessity of the above transparent conductive film 2.
(3) Next, either CdTe molecules or Cd and Te with corresponding mole fraction are deposited 1 to 10 .mu.m thick by means of a screen printing method, an electrolytic plating method, a spray method, or the like.
(4) Cadmium chloride (CdCl.sub.2) or chlorine (Cl.sub.2) is then mixed with or added to such CdTe molecules or Cd and Te with corresponding mole fraction in proper quantity. In turn, a resultant structure is annealed in an air or an inert gas at a temperature of 350 to 700.degree. C. for about 0.1 to 2 hours to thus obtain the p-type CdTe layer 4 which has a substantially equal stoichiometry.
(5) Finally, the ohmic electrode
Agui Takaaki
Takamoto Tatsuya
Chapman Mark
Japan Energy Corporation
LandOfFree
Method of producing photoelectric conversion device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of producing photoelectric conversion device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing photoelectric conversion device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1372643