HAL Id: hal-01660154
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Submitted on 12 Dec 2017
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Towards III-V on silicon solar cells
Mickael da Silva, S. Boyer-Richard, C. Cornet, Antoine Létoublon, Christophe Levallois, Alain Rolland, Jacky Even, Laurent Pedesseau, Alain Le Corre,
Slimane Loualiche, et al.
To cite this version:
Mickael da Silva, S. Boyer-Richard, C. Cornet, Antoine Létoublon, Christophe Levallois, et al.. To-wards III-V on silicon solar cells. 7è Journées Nationales du PhotoVoltaïque (JNPV 2017), Dec 2017, Dourdan, France. 107, pp.191603 - 191603, 2015. �hal-01660154�
M. Da Silva
1, S. Boyer-Richard
1, C. Cornet
1, A. Létoublon
1, C. Levallois
1, A. Rolland
1, J. Even
1, L. Pédesseau
1, A. Le Corre
1,
S. Loualiche
1, L. Lombez
2, J.-F. Guillemoles
2, F. Mandorlo
3, M. Lemiti
3, and O. Durand
11
UMR FOTON, CNRS, INSA de Rennes, F-35708 Rennes, France
2
IRDEP, UMR 7174 CNRS-EDF-ENSCP, 6 Quai Watier-BP 49, 78401 Chatou Cedex, France
3
University of Lyon, Lyon Institute of Nanotechnology (INL) UMR CNRS 5270, INSA de Lyon, Villeurbanne, France
[email protected]
Towards III-V on silicon solar cells
N and As decrease the GaP bandgap from 2.3 eV to 1.7 eV and ensure the lattice
matching with Si
Main challenges:
Ohmic contacts on GaP (n:Ni/Au/Ge and p:Ti/Pt/Au on GaAsP p++)
Reducing the surface recombination velocity
Improving optoelectronic properties of the III-V absorber
III-V/Si interface (Si/GaP pseudo-substrate)
Efficient tunnel junction between III-V and Si based materials
GaAsPN
Front contact
Passivation layer III-N-V pin junction
Tunnel junction Si pn junction
Back contact
GaP/Si heterojunctions for photovoltaics
Tandem cells on silicon : high performance of multijunction
solar cells on a classical photovoltaic substrate : silicon
Epitaxial GaP layer as a transparent conductive layer on a
single junction silicon solar cell to limit Si(n) absorption
GaP(n)/Si(p) heterojunction to enhance V
ocand high energy
absorption
GaAsPN on Si tandem cells: high efficiency and low cost
-1,0 -0,5 0,0 0,5 -15 -10 -5 0 5 10 Voc = 0,28 V Jsc = 14,23 mA/cm² FF = 48,8 % η = 1,96 % j (m A /c m ²)
V (V)
dark AM 1.5 Si(n+) Si(p+) TJ Si(n++)/Si(p++) GaP(n+) 300 nm GaAsPN(i) 300 nm GaP(p++) 30 nmEncouraging photovoltaic effect.
Non optimal regrowth due to new TJ process
→ low surface quality → interfacial recombinations = low Voc ?
Optimizing GaP/Si interface
Cross-sectional HRSTEM image of GaP epilayer grown on Si substrate
Ping Wang, Y., Appl. Phys. Lett. 107, 191603 (2015)
State-of-the art GaP/Si(001) platform : Very low density of micro-twins
annihilation of the antiphase domains after only 10 nm GaP growth But doping GaP at the Si interface remains challenging
GaP MBE 35 nm (500°C) GaP MEE 10 nm (350°C)
Si (001) substrate
AFM : Weak roughness (RMS 0.3 nm)
Ohmic contacts on GaP
Direct p-type ohmic contact on GaP requires exotic metal : Pd/Zn/Pd
Supplementary epitaxial GaAsP allows to use Ti/Pt/Au
20 nm GaAs0,1P0,9 heavily doped : Na=3. 1019 cm-3 Ohmic contact on GaP :
ρc = 4.10-6 Ω.cm2 after 35s annealing @ 375°C
Attempt of GaP/Si heterojunction solar cell
0 10 20 30 40 50 60 70 300 500 700 900 1100 E Q E ( % ) λ (nm) Si (p) 300 µm substrate GaP/AlGaP(n++) 20 nm GaAsP(n++) 100 nm
External quantum efficiency max : 63.5%
Drop of EQE at short wavelength due to surface recombination at the n-GaP surface and diffusion length on the GaP side
Si side: limited by the
diffusion length of carriers in Si substrate (thinner substrate)
Poor electrical performances due to very bad contact on the Si side and carrier trapping at the doped GaP/Si interface : VOC= 0,244 V, Efficiency : 0.45 %
Doping the GaP layer at the vicinity of the GaP/Si interface is a very strong issue because dopants seem to accumulate at APBs locally overpassing the solubility limit.
Further work :
optimizing Si contact and GaP/Si interface with dopants
Using the GaP layer as transparent conductive layer on a Si homojunction
First tandem cell on VPE Si pn junction
GaP top cell optimization
Several studies already performed :
Absorber layer optimization : Tg = 480°C, V/III = 10-11, Gr = 0,5ML/s Low carrier mobility in GaAsPN: 300 nm-thick absorber
Optimized composition : GaAs0,1P0.88N0.02 : pseudo-direct gap @ 1.7 eV, lattice matched to silicon
New study : optimization of the n-doped layer
1,8 2,0 2,2 2,4 2,6 2,8 3,0 3,2 3,4 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,10 0,11 2.1018 cm-3 G a P d ir e c t 2 .7 2 e V G a P i n d ir e c t 2 .1 9 e V E Q E ( % ) Energy (eV) 1 2 3 4 5 6 1,8 2,0 2,2 2,4 2,6 2,8 3,0 3,2 3,4 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,10 0,11 2 .7 e V 2 .1 7 e V G a P i n d ir e c t G a P d ir e c t 8.1018 cm-3 E Q E ( % ) Energy (eV) 1 2 3 4 5 6 7 8
Low energy peak increases with n doping level: better current collection near the GaAsPN/GaP:n interface
