The status of the technology associated with the development of high output voltage silicon solar cells is reported. The energy conversion efficiency of a double diffusion process is compared to that of a single diffusion process. The efficiency of a 0.1 ohm/cm solar cell is characterized both before and after covering

Allison, J. F.

Arndt, R. A.

Muelenberg, A.

Weizer, V.

English

NASA Technical Reports Server

RECENT PROGRESS IN HIGH-OUTPUT-VOLTAGE SILICON SOLAR CELLS" 
A. Meulenberg, R. A. Arnat,  a n d  J. F. Allison 
COMSAT Laboratories 
Clarksburg, Maryland 
and 
V. Weizer 
N ASA Lewis Research Center  
Cleveland, Ohio 
High-quality shallow- junction planar solar cells have been fabricated on 
0.1 Q-cm float zone refined silicon using Emulsitone N250 spin-on dopant, 
aluminum-alloyed back contacts, and "dot" contact front grids (ref. 1). Use 
of a process similar to the NASA-Lewis double-diffusion process (ref. 2) has 
reduced shunt leakage and junction recombinztion currents while adding 10 mV 
to the best open-circuit voltages obtained from the single-diffusion process. 
The present status of a 0.1-Q-cm covered solar cell (153-mA short-circuit, 
654-mV open-circuit voltage, 77.5-mW maximum power, and 14.4-percent AM0 
efficiency) is characterized in figure 1 before and after covering. The short- 
circuit current (ISC) is about 6 percent less than that observed in typical 
higher resistivity (21-Q-cm) violet cells (ref. 3) but the open-circuit voltage 
(VOC) is about 9 percent higher. During covering or subsequent handling, the 
cell fill factor was reduced in an unexplained manner (analysis indicates a 
lowered shunt resistance). 
have exceeded 79.5 mW. 
If it had been maintained, the maximum power would 
The quantum-yield data are presented in figure 2 along with data from 
a deeper junction cell 
(x. N 0.1 pm) cell made byjadifferent process. 
fiiure is the unusual shape of the set A curves. 
surface dead layer displays a much more abrupt drop in the short wavelength 
region rather than the more gentle the slopes observed in figure 2 below 700 nm. 
It would appear that the double-diffusion process alters the cell characteristics 
in a manner quite different than expected from a simple change in the diffused 
layer (see ref. 2 for a possible explanation). 
with N250 at 88OOC followed by different etch times prior to an N250 diffusion 
at 820OC for 15 minutes; set B was diffused with N250 at 820OC for 15 minutes. 
(x - 1.6 pm) from the same batch and a shallow junction 
An important feature of this 
A conventional cell with a 
Set A had an overnight diffusion 
The advantages of a 2-step diffusion process are delineated by com- 
parisons of the data from two sets of cells (table I). 
several differences resulting from a prediffusion; most important are a 10-mV 
increase in VOC and an improved fill factor of set A. 
explained by the lower bulk dark current (JD); the better fill factor (FF) is 
2This paper is based upon work performed at COMSAT Laboratories under the 
The data indicate 
The improved VOC is 
joint sponsorship of NASA, under Contract NAS-3-22217, and the Communications 
Satellite Corporation. 
11 
https://ntrs.nasa.gov/search.jsp?R=19810009012 2020-03-21T08:58:56+00:00Z
due to the lower preexponential of the n = 2 term (JRC) and higher shunt 
resistance (RSH). 
in figure 2. The long wavelength response (A > 1000 nm) and the currents 
(I ) from y-ray irradiation of the two sets are nearly equal and indicate 
dizfusion lengths comparable to or greater than the cell thickness (200 pm). 
This point is supported by the values of ISC in set B, which are almost as high 
as those for 1- to 2-R-cm violet cells. 
The penalty is reduced ISC agd blue response (IB), as seen 
Efforts are continuing to better understand the mechanism responsible 
for increased voltage resulting from the double-diffusion process. 
mechanism is understood, work can be directed toward further voltage gains and 
reduction of short-circuit current losses. 
Once this 
1. 
2. 
3.  
REFERENCES 
Lindmayer, J. ;  and Allison, J. F. :  Dotted Contact Fine Geometry Solar Cell. 
U.S. Patent 3,982,964, Sept. 28, 1976. 
Godlewski, M. P. ;  Klucker, T. M.; Mazaris, G. A.; and Weizer, V. G.: Open- 
Circuit Voltage Improvements in Low Resistivity Solar Cells. 14th IEEE 
Photovoltaic Specialists Conference, Jan. 7-10, 1980, San Diego, CA, 
Proc., pp. 166-171. 
Haynos, J.G.; Allison, J. F.;  Arndt, R. A,; and Meulenberg, A.: The COMSAT 
Non-Reflective Silicon Solar Cell: 
International Conf. on Photovoltaic Power Generation, Sept. 1974, Hamburg, 
Germany, Proc., pp. 487-500. 
A Second Generation Improved Cell, 
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with Shallow (B-3) and Deep (A-1) Junct ion C e l l s  
14 


Recent progress in high-output-voltage silicon solar cells

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