US 4,395,583 A · Optimized back contact for solar cells

Abstract

The surface recombination velocity at the back portion of a solar cell is reduced in a first embodiment by reducing the back surface metal contact area without increasing series resistance. The back surface is provided with a p.sup.+ layer deposited on the solar cell p layer in order to further reduce the surface recombination velocity and therefore the diffusion current generated in the back layer of the cell. The p.sup.+ layer is provided with an oxide coating. Micro holes are etched through the oxide layer, and a thin layer of metal is evaporated over the entire surface. In a second embodiment the surface recombination velocity at the back portion of the cell is reduced by depositing a thin non-conductive coating on the p.sup.+ layer. A selected metal coating is then deposited on the non-conductive coating to thereby form a Mott-Schottky barrier, the metal coating retarding the transport of minority carriers through the non-conductive coating without impeding the flow of majority carriers through the non-conductive coating. In a third embodiment, the surface recombination velocity is reduced by depositing a conductive oxide on the p.sup.+ layer, and a metal coating is further deposited on the conductive oxide coating. The conductive oxide coating reduces surface recombination at the interface of the p.sup.+ and conductive oxide layers, and provides majority carriers to the p.sup.+ layer.

Claims28

Dependent claims

A solar cell having a first extrinsic semiconductor layer providing majority carriers of a first electrical charge, a second semiconductor layer adjacent to said first layer, and a back contact optimized to reduce effective surface recombination, said optimized back contact comprising:

(a) a third extrinsic semiconductor layer having a thickness (W) substantially less than its minority carrier diffusion length (L), adjacent to said second layer to form a first interface having a low effective surface recombination velocity, said third layer providing a number of majority carriers of a second electrical charge opposite to said first electrical charge;
(b) a non-metallic coating deposited on said third layer to form a second interface having a low surface recombination velocity, said non-metallic coating having a plurality of micro holes provided therethrough, the total area of said micro holes being small relative to the total area of said non-metallic coating;
and
(c) a metal coating deposited on said non-metallic coating to thereby provide electrical contacts from said metal coating to said third layer through said micro holes to form a third interface at said electrical contacts,
wherein the ratio (W/L) of the width (W) of said third layer to the minority carrier diffusion length (L) in said third layer is chosen so as to reduce the quantity:
##EQU9## below (x/y)(D/L) where x and y are the minority carrier concentrations in said third and second layers, respectively;
D is the minority carrier diffusion coefficient of said third layer;
and A.sub.o, A.sub.m and A.sub.total are the relative areas of said second, third and first interfaces, respectively.

5 more elements

(a) a third extrinsic semiconductor layer having a thickness (W) substantially less than its minority carrier diffusion length (L), adjacent to said second layer to form a first interface having a low effective surface recombination velocity, said third layer providing a number of majority carriers of a second electrical charge opposite to said first electrical charge;
(b) an electrically conductive non-metallic coating deposited on said third layer to form a second interface having a low surface recombination velocity, said non-metallic coating having a plurality of micro holes provided therethrough, the total area of said micro holes being small relative to the total area of said non-metallic coating;
and
(c) a metal coating deposited on said non-metallic coating to thereby provide electrical contacts from said metal coating to said third layer through said micro holes to form a third interface at said electrical contacts,
wherein the ratio (W/L) of the width (W) of said third layer to the minority carrier diffusion length (L) in said third layer is chosen to minimize the quantity:
##EQU10## where x and y are the minority carrier concentrations in said third and second layers, respectively;
D is the minority carrier diffusion coefficient of said third layer;
and A.sub.o, A.sub.m and A.sub.total are the relative areas of said second, third and first interfaces, respectively.

5 more elements

Dependencies are inferred from the claim text.

Optimized back contact for solar cells

Life of this patent

Optimized back contact for solar cells

Life of this patent

Abstract

Claims28