Details
| Original language | English |
|---|---|
| Article number | 8565997 |
| Pages (from-to) | 89-96 |
| Number of pages | 8 |
| Journal | IEEE journal of photovoltaics |
| Volume | 9 |
| Issue number | 1 |
| Publication status | Published - Jan 2019 |
Abstract
We investigate the enhancement in transparency and conductivity of aluminum doped zinc oxide (ZnO:Al) layers upon high-Temperature annealing and its impact on contact resistance, as well as, on passivation properties of carrier selective junctions based on doped polycrystalline Si on a passivating silicon oxide (POLO). The temperature stability of these junctions allows annealing of the ZnO:Al/POLO combination up to 600 °C. We prepare ZnO:Al films by dc magnetron sputtering at room temperature. We determine the complex refractive index of ZnO:Al in dependence of post-deposition annealing (PDA) temperature by spectroscopic ellipsometry. High-Temperature annealing improves the conductivity and reduces the absorption within ZnO:Al. The optical losses in a ZnO:Al/POLO stack are rather limited by the poly-Si layer than by the ZnO:Al. The sheet resistance improves from roughly 20000 Ω/sq for 80 nm thick as-deposited ZnO:Al films to 72 Ω/sq after fast firing at 600 °C. At the same time, PDA cures the damage induced in the POLO junctions during ZnO:Al deposition. After PDA with AlxOy capping layers, the passivation quality even surpasses the initial level. A transmission electron microscopy analysis of the interface between the ZnO:Al and the underlying poly-Si reveals the formation of a silicon oxide like interfacial layer after PDA at 400 °C. This interfacial layer causes a high contact resistivity of the metal/ZnO:Al/POLO-junction and could limit the thermal budget for cell processing. Our results indicate that after successful process adjustment, ZnO:Al could substitute In-based transparent conductive oxides on POLO cells for cost reasons, as well as, enable a high efficiency potential.
Keywords
- Passivating contacts, POLO junction, polycrystalline silicon, thermal treatment, ZnO:Al
ASJC Scopus subject areas
- Materials Science(all)
- Electronic, Optical and Magnetic Materials
- Physics and Astronomy(all)
- Condensed Matter Physics
- Engineering(all)
- Electrical and Electronic Engineering
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In: IEEE journal of photovoltaics, Vol. 9, No. 1, 8565997, 01.2019, p. 89-96.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - High Temperature Annealing of ZnO:Al on Passivating POLO Junctions
T2 - Impact on Transparency, Conductivity, Junction Passivation, and Interface Stability
AU - Wietler, Tobias F.
AU - Min, Byungsul
AU - Reiter, Sina
AU - Larionova, Yevgeniya
AU - Reineke-Koch, Rolf
AU - Heinemeyer, Frank
AU - Brendel, Rolf
AU - Feldhoff, Armin
AU - Krugener, Jan
AU - Tetzlaff, Dominic
AU - Peibst, Robby
N1 - Funding information: December 21, 2018. This work was supported in part by the Ministry for Science tablished concept to realize such junctions is the application of andCultureofLowerSaxony,theGermanMinistryforEconomicAffairsand heterojunctions using surface passivating intrinsic and doped Horizon2020researchandinnovationprogramunderGrant727529(DISC).EnergyunderGrant0325702(POLO)andinpartbytheEuropeanUnion’s hydrogenated amorphous silicon (a-Si:H) layers on the front (Corresponding author: Tobias F. Wietler.) and rear side of the solar cell [2], [3]. An alternative also with T.F.Wietler,B.Min,S.Reiter,Y.Larionova,R.Reineke-Koch,F.Heine- excellent interface passivation quality is the junction between merthal31860,Germany(e-mail:,wietler@isfh.de;min@isfh.de;reiter@isfh.meyerarewiththeInstituteforSolarEnergyResearchHamelin(ISFH),Em- crystalline (c-) and polycrystalline (poly-) silicon with an em-de; larionova@isfh.de; r.reineke-koch@isfh.de; heinemeyer@isfh.de). bedded interfacial silicon oxide (POLO) [4], [5]. Very low re-R.BrendeliswiththeInstituteforSolidStatePhysics,LeibnizUniversita¨t combination current densities enable a conversion efficiency of ergyResearchHamelin(ISFH),Emmerthal31860,Germany(e-mail:,brendel@Hannover,Hanover30167,Germany,andalsowiththeInstituteforSolarEn- 26.1% for a POLO-cell with interdigitated back contacts [6]. isfh.de). Over a wide range of the spectrum, doped poly-Si has a lower J.Kru¨generiswiththeInstituteofElectronicMaterialsandDevices(MBE), absorption coefficient than doped a-Si:H, implying a signifi-A.Feldhoff is withtheInstituteforPhysical Chemistryand Electro-Hanover30167,Germany(e-mail:,kruegener@mbe.uni-hannover.de). cantly lower absorption loss in a poly-Si layer than in an a-Si:H chemistry, Leibniz Universität Hannover, Hanover 30167, Germany (e-mail:, layer with the same thickness [7]–[9]. For a 15 nm thick, doped armin.feldhoff@pci.uni-hannover.de). poly-Si layer, for example, the parasitic absorption induces a sita¨tBraunschweig,Braunschweig38106,Germany(e-mail:,dominic.tetzlaff@D.Tetzlaff is withthe Instituteof AppliedPhysics,Technische Univer- loss in the short-circuit current density of 0.75 mA/cm2. For a tu-braunschweig.de). doped a-Si:H layer with the same thickness, the corresponding R.PeibstiswiththeInstituteforSolarEnergyResearchHamelin(ISFH), loss is 3 mA/cm2 [7]. However, less than 20 nm thin poly-Si andDevices(MBE),Hanover30167,Germany(e-mail:,peibst@isfh.de).Emmerthal31860,Germany,andalsowiththeInstituteofElectronicMaterials layers have sheet resistances above 1000 ?/sq [10]. A highly This paper has supplementary downloadable material available at conductive and transparent layer on top of the poly-Si could help http://ieeexplore.ieee.orgprovidedbytheauthor. to ensure the required lateral conductivity for the transport of athttp://ieeexplore.ieee.org.Colorversionsofoneormoreofthefiguresinthispaperareavailableonline charge carriers toward the metallization grid on the front side. German Ministry for Economic Affairs and Energy under Grant 0325702
PY - 2019/1
Y1 - 2019/1
N2 - We investigate the enhancement in transparency and conductivity of aluminum doped zinc oxide (ZnO:Al) layers upon high-Temperature annealing and its impact on contact resistance, as well as, on passivation properties of carrier selective junctions based on doped polycrystalline Si on a passivating silicon oxide (POLO). The temperature stability of these junctions allows annealing of the ZnO:Al/POLO combination up to 600 °C. We prepare ZnO:Al films by dc magnetron sputtering at room temperature. We determine the complex refractive index of ZnO:Al in dependence of post-deposition annealing (PDA) temperature by spectroscopic ellipsometry. High-Temperature annealing improves the conductivity and reduces the absorption within ZnO:Al. The optical losses in a ZnO:Al/POLO stack are rather limited by the poly-Si layer than by the ZnO:Al. The sheet resistance improves from roughly 20000 Ω/sq for 80 nm thick as-deposited ZnO:Al films to 72 Ω/sq after fast firing at 600 °C. At the same time, PDA cures the damage induced in the POLO junctions during ZnO:Al deposition. After PDA with AlxOy capping layers, the passivation quality even surpasses the initial level. A transmission electron microscopy analysis of the interface between the ZnO:Al and the underlying poly-Si reveals the formation of a silicon oxide like interfacial layer after PDA at 400 °C. This interfacial layer causes a high contact resistivity of the metal/ZnO:Al/POLO-junction and could limit the thermal budget for cell processing. Our results indicate that after successful process adjustment, ZnO:Al could substitute In-based transparent conductive oxides on POLO cells for cost reasons, as well as, enable a high efficiency potential.
AB - We investigate the enhancement in transparency and conductivity of aluminum doped zinc oxide (ZnO:Al) layers upon high-Temperature annealing and its impact on contact resistance, as well as, on passivation properties of carrier selective junctions based on doped polycrystalline Si on a passivating silicon oxide (POLO). The temperature stability of these junctions allows annealing of the ZnO:Al/POLO combination up to 600 °C. We prepare ZnO:Al films by dc magnetron sputtering at room temperature. We determine the complex refractive index of ZnO:Al in dependence of post-deposition annealing (PDA) temperature by spectroscopic ellipsometry. High-Temperature annealing improves the conductivity and reduces the absorption within ZnO:Al. The optical losses in a ZnO:Al/POLO stack are rather limited by the poly-Si layer than by the ZnO:Al. The sheet resistance improves from roughly 20000 Ω/sq for 80 nm thick as-deposited ZnO:Al films to 72 Ω/sq after fast firing at 600 °C. At the same time, PDA cures the damage induced in the POLO junctions during ZnO:Al deposition. After PDA with AlxOy capping layers, the passivation quality even surpasses the initial level. A transmission electron microscopy analysis of the interface between the ZnO:Al and the underlying poly-Si reveals the formation of a silicon oxide like interfacial layer after PDA at 400 °C. This interfacial layer causes a high contact resistivity of the metal/ZnO:Al/POLO-junction and could limit the thermal budget for cell processing. Our results indicate that after successful process adjustment, ZnO:Al could substitute In-based transparent conductive oxides on POLO cells for cost reasons, as well as, enable a high efficiency potential.
KW - Passivating contacts
KW - POLO junction
KW - polycrystalline silicon
KW - thermal treatment
KW - ZnO:Al
UR - http://www.scopus.com/inward/record.url?scp=85058069936&partnerID=8YFLogxK
U2 - 10.1109/JPHOTOV.2018.2878337
DO - 10.1109/JPHOTOV.2018.2878337
M3 - Article
AN - SCOPUS:85058069936
VL - 9
SP - 89
EP - 96
JO - IEEE journal of photovoltaics
JF - IEEE journal of photovoltaics
SN - 2156-3381
IS - 1
M1 - 8565997
ER -