Test results indicate that solder coating cells produces protective or deleterious effect, depending on the environment. Major problem for solder coated cells is in control of solder thickness and uniformity. Problem area for non-solder coated cells is not identified

Berman, P. A.

Moss, R. W.

English

NASA Technical Reports Server

August 1971
Brief 71-10282 
NASA TECH BRIEF 
NASA Pasadena Office 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the. Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Environmental Effects on Silicon Solar Cells 
A series of environmental tests was performed 
on batches of silicon solar cells having titanium-
silver contacts, with and without solder coating, to 
determine the effects of these environments on the 
mechanical and electrical properties of the cells. 
The tests were initiated because of a major problem 
encountered by users of silicon solar cells, i.e., the 
loss of contact pull strength after exposure to various 
environments. This loss can be so severe in vacuum 
metallized silver over titanium (Ag-Ti) contacts that 
it is necessary to put a protective layer of lead-tin-
silver solder (36 Pb, 62 Sri, 2 Ag) over the contact 
strips. While this solder coating protects the Ag-Ti 
contacts from environmental attack, it creates other 
problems, such as adding the weight of the solder, 
producing a thermal shock in the cell during solder 
dipping, and increasing the possibility of cell crack-
ing or delamination during thermal cycling, due to 
excessively heavy or uneven solder coating. 
The cells analyzed in the experimental program 
represented two main types: N on P, 0.04 cm thick 
cells with solder-coated Ag-Ti confacts; and N on 
P, 0.02 cm thick cells with nonsolder-coated Ag-Ti 
contacts. 
Cells with solder coating exhibited the largest 
electrical and mechanical degradations after ex-
posure to a series of five thermal cycles from 408 to 
77 K. Cells without solder coating exhibited the 
largest mechanical degradation after a 36 hour ex-
posure at 418 K. The latter, however, did not result 
in significant electrical degradation. Thus, the 
presence of solder coating on solar cells can have 
a protective or deleterious effect, depending on 
the environment.
It was observed that either solder-coated or 
nonsolder-coated cells were capable of surviving 
all the environmental tests with essentially no deg-
radation indicating that problems were in the process 
controls rather than in the basic cell process. Anal-
ysis indicated that, in the case of solder-coated 
cells, the major problem was in the control of 
solder thickness and uniformity. In the case of non-
solder-coated cells, the major problem area was not 
identified; however, it was postulated that more than 
one mechanism was operating since it was not pos-
sible to correlate electrical degradation with contact 
pull-strength degradation. 
Note: 
The following documentation may be obtained 
from:
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: 
NASA-TR-321362 (N69-18012), Effects of 
Environmental Exposures on Silicon Solar 
Cells 
Patent status: 
No patent action is contemplated by NASA. 
Source: . R. Moss and P. Berman of

Caltech/JPL
under contract to

NASA Pasadena Office

(N PO- 1 1475) 
Category 02 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19710000281 2020-03-17T02:20:43+00:00Z


Environmental effects on silicon solar cells

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