DESIGN OF A THREE-LAYER ANTIREFLECTION COATING FOR HIGHEFFICIENCY INDIUM PHOS

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DESIGN OF A THREE-LAYER ANTIREFLECTION COATING FOR HIGHEFFICIENCY INDIUM PHOSPHIDE SOLAR CELLSUSING A CHEMICAL OXIDE AS FIRST LAYER
Jacques Moutot
% _: _; @0 y; L! @$ k4 ~4 _Cleveland State University,
  V- @8 O9 _8 i' I) N0 x7 \Cleveland, Ohio 441 15
Mircea Faur
Cleveland State University,
3 M! ~  V3 x" _9 Q# S* x- WCleveland, Ohio 441 15
2 N. _# [- y, `( b4 AMaria Faur
NASA Lewis Research Center
Cleveland, Ohio 44135
Chandra Goradia
: F8 H, s/ ]0 ?5 ^' j/ k, CCleveland State University,
Cleveland, Ohio 441 15
0 v" a3 H+ a7 O$ F" C1 Y2 J, S8 eManju Goradia
9 h3 A" D% ?1 c  y& ICleveland State University,
Cleveland, Ohio 441 15
) h8 \6 }7 o, y8 hSheila Bailey
NASA Lewis Research Center
Cleveland, Ohio 441 35
" }9 ]& P' M+ UABSTRACT
7 I' V; D8 ?; u' ~It is well known that the behavior of Ill-V compound based solar cells is largely controlled
# B& Q# ~& j* r. N- x; P: b- l, W4 oby their surface, since the majority of light generated carriers (63% for GaAs and 79% for InP)
9 W0 w0 Z7 X  {9 I  p; Q, tare created within 0.2 ym of the illuminated surface of the cell. Consequently, the always
observed high surface recombination velocity (SRV) on these cells is a serious limiting factor for
their high efficiency performance, especially for those with the pn junction made by either
thermal diffusion or ion implantation. A good surface passivation layer, ideally, a grown oxide as
  a. W6 [% U: K* v8 _8 c, M. mopposed to a deposited one, will cause a significant reduction in the SRV without adding
1 |8 @# S. X% D, l9 Ainterface problems, thus improving the performance of Ill-V compound based solar cells. Another
significant benefit to the overall performance of the solar cells can be achieved by a substantial
reduction of their large surface optical reflection by the use of a well designed antireflection (AR)
coating.
- W' u, }, z6 |% L% f4 RIn this paper, we demonstrate the effectiveness of using a chemically grown, thermally
and chemically stable oxide, not only for surface passivation but also as an integral part of a 3-
, l" ^" Q6 B" o' ~1 }layer AR coating for thermally diffused p"n InP solar cells. A phosphorus-rich interfacial oxide,
; m5 }' V, v0 X% ?  L5 QIn(PO3)3, is grown at the surface of the p' emitter using an etchant based on HNO3, o-H3P04
and H202. This oxide has the unique properties of passivating the surface as well as serving as
- q$ z9 w% N: ?' P& i+ ]a failly efficient antireflective layer yielding a measured record high AMO, 25OC, open-circuit
voltage of 890.3 mV on a thermally diffused InP(Cd,S) solar cell. Unlike conventional single
$ q5 F# ~( ]1 t/ Q2 ]layer AR coatings such as ZnS, Sb2O3, Si0 or double layer AR coatings such as ZnSIMgF2
deposited by e-beam or resistive evaporation, this oxide preserves the stochoimetry of the InP
1 d0 ]) D. ^1 y9 d7 psurface. We show that it is possible to design a three-layer AR coating for a thermally diffused
7 U9 ^1 h6 f$ v) k$ X3 y% I. u# U0 J" iInP solar cell using the ln(P03)3 grown oxide as the first layer and AI203 , MgF2 or ZnS, MgF2
1 u2 L# b  f. l+ w8 a2 A( j, }as the second and third layers respectively, so as to yield an overall theoretical reflectance of
less than 2%