Light-induced degradation due to Cu precipitation in crystalline silicon: Modeling and impact on PERC solar cells

Henri Vahlman

Light-induced degradation due to Cu precipitation in crystalline silicon: Modeling and impact on PERC solar cells

Julkaisun otsikon käännös: Kuparin erkautumisen aiheuttama valodegradaatio kiteisessä piissä: Mallinnus ja vaikutukset aurinkokennoihin

Henri Vahlman

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Kupari on yleinen alkuaine, ja siten hankalasti kontrolloitava epäpuhtaus piikomponenttien tuotantolinjoilla. Jo hyvin pienet kuparikonsentraatiot p-tyypin piikomponenteissa (esim. aurinko- kennoissa) voivat johtaa kuparin aiheuttamaan valodegradaatioon, eli vähemmistövarauksen- kuljettajien bulkkielinajan lyhenemiseen ylimäärävarauksenkuljettajainjektion aikana. Jo analyyttisten mittausmenetelmien herkkyysrajat alittavat kuparikonsentraatiot voivat johtaa kuparin aiheuttamaan valodegradaatioon. Siksi on tärkeää tunnistaa kyseinen ilmiö suoraan komponenttitason vaikutuksista, jotka voivat sekoittua samanaikaisesti ilmeneviin muihin valo- degradaatiomekanismeihin. Tämän työn ensimmäinen tavoite on selkeyttää niitä aurinkokenno- tasolla ilmeneviä piirteitä, joita voidaan hyödyntää kuparin aiheuttaman valodegradaation erottamisessa muista valodegradaatiomekanismeista. Teollisissa passivoidun emitterin ja takaosan omaavissa aurinkokennoissa ilmennyttä voimakasta valodegradaatiota karakterisoitiin, ja analyysiä täydennettiin tutkimalla koronavarauksen vaikutusta elinaikanäytteissä, jota on aiemmin käytetty menetelmänä kuparin aiheuttaman valodegradaation tunnistamisessa. Tuloksista ilmenee, että aurinkokennojen kupariin liittyvä valodegradaatio voidaan tunnistaa suhteellisen nopean degradaationopeuden perusteella, sekä hiladefektien päällä ilmenevästä voimakkaasta degradaatiosta. Kupariin liittyvän valodegradaation ja toisen valodegradaatiomekanismin, ns. Sponge-LID:n välillä kuitenkin havaittiin samankaltaisia ominaisuuksia, ja lisätutkimukset esim. elinaikaspektroskopiaa hyödyntäen ovat tarpeen näiden mekanismien suhteen selkeyttämiseksi. Työn toinen tavoite on syventää kuparin aiheuttamaan valodegradaatioon liittyvää teoreettista ymmärrystä. Tämän tavoitteen saavuttamiseksi johdettiin fysikaalinen malli perustuen sähkö- staattisten vaikutusten rajoittamaan kuparin erkautumiseen, joka yhdessä aiemmin julkaistun metallierkaumien Schottky-liitosmallin kanssa mahdollistaa kupariin liittyvän valodegradaation mallintamisen suoraan vähemmistövarauksenkuljettajien elinajan tasolla. Mallin ja kokeiden välillä havaittiin yhdenmukaisuus useimmissa tutkituista tapauksista. Kuparin aiheuttaman valo- degradaation voimakkuus riippuu teoreettisesti pääosin kupari- ja seostuskonsentraatioista, ja heterogeenisten ydintymispaikkojen tiheydestä. Kaikki ym. suureet vaikuttavat erkaumien lopulliseen kokoon, joiden säteen pääteltiin olevan muutamien ja muutamien kymmenien nanometrien välillä. Yllämainitut tulokset vahvistavat erkautumisteoriaa kuparin aiheuttaman valoerkautumisen perimmäisenä syynä, ja antavat näkemyksiä kyseisen häviömekanismin aiheuttamien vaikutusten pienentämiseen piikomponenteissa.

Julkaisun otsikon käännös	Kuparin erkautumisen aiheuttama valodegradaatio kiteisessä piissä: Mallinnus ja vaikutukset aurinkokennoihin
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Savin, Hele, Vastuuprofessori Savin, Hele, Ohjaaja Haarahiltunen, Antti, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-7921-9
Sähköinen ISBN	978-952-60-7922-6
Tila	Julkaistu - 2018
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

pii
aurinkokenno
kupari
valodegradaatio
erkautuminen

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-60-7922-6Lisenssi: Määrittelemätön

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Rissanen, A. (Manager)
Aalto-yliopisto
Laitteistot/tilat: Facility
OtaNano Nanofab
Repo, P. (Manager) & Rissanen, A. (Other)
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Laitteistot/tilat: Facility

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@phdthesis{0e0abf717c784ab8b8ea9e071074b20e,

title = "Light-induced degradation due to Cu precipitation in crystalline silicon: Modeling and impact on PERC solar cells",

abstract = "Copper is a common element in the environment and hence a difficult contaminant to control on silicon device manufacture lines. In p-type Si devices (e.g. solar cells), even very low copper concentrations can lead to copper-related light-induced degradation (Cu-LID), that is, degradation of the bulk minority carrier lifetime under excess carrier injection. As copper concentrations even below the detection limits of analytical methods can cause Cu-LID, it is necessary to identify its presence directly from device-level effects, which can be perturbed by the simultaneous occurrence of other light-induced degradation (LID) mechanisms. Hence, the first aim of this work is to clarify the properties of Cu-LID that enable its distinction from other LID mechanisms at the solar cell level. Thus, strong LID observed in industrial passivated emitter and rear contact (PERC) solar cells was characterized, and complemented with an analysis of the effects of corona charging on lifetime sample wafers; a method that has earlier been used in the detection of Cu-LID. The results reveal that Cu-LID in solar cells can be recognized based on its relatively fast degradation rate and laterally heavy degradation patterns on extended defects. On the other hand, Cu-LID and another LID mechanism called Sponge-LID showed mutually similar properties, and further investigations possibly involving lifetime spectroscopic methods are necessary to clarify their relationship. The second objective of the thesis is to deepen the theoretical understanding of Cu-LID. Hence, a physical model based on a theory of electrostatically limited copper precipitation was derived, which together with a previously published Schottky junction model of metal precipitates enables the modeling of Cu-LID directly at the minority carrier lifetime level. Agreement between the model and experiments was obtained in most of the investigated cases. Consequently, the different material properties and environmental conditions that affect the strength of Cu-LID were identified. Theoretically, the strength of Cu-LID is mostly affected by the Cu and the doping concentrations, and the density of heterogeneous nucleation sites, all of which influence the final precipitate size that was found to reside between few to few tens of nanometers in radius. These results provide confirmation for the precipitation theory of Cu-LID, and provide insights for mitigating its effects in silicon devices.",

keywords = "silicon, solar cell, copper, LID, precipitation, pii, aurinkokenno, kupari, valodegradaatio, erkautuminen, silicon, solar cell, copper, LID, precipitation",

author = "Henri Vahlman",

year = "2018",

language = "English",

isbn = "978-952-60-7921-9",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "59",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - Light-induced degradation due to Cu precipitation in crystalline silicon: Modeling and impact on PERC solar cells

AU - Vahlman, Henri

PY - 2018

Y1 - 2018

N2 - Copper is a common element in the environment and hence a difficult contaminant to control on silicon device manufacture lines. In p-type Si devices (e.g. solar cells), even very low copper concentrations can lead to copper-related light-induced degradation (Cu-LID), that is, degradation of the bulk minority carrier lifetime under excess carrier injection. As copper concentrations even below the detection limits of analytical methods can cause Cu-LID, it is necessary to identify its presence directly from device-level effects, which can be perturbed by the simultaneous occurrence of other light-induced degradation (LID) mechanisms. Hence, the first aim of this work is to clarify the properties of Cu-LID that enable its distinction from other LID mechanisms at the solar cell level. Thus, strong LID observed in industrial passivated emitter and rear contact (PERC) solar cells was characterized, and complemented with an analysis of the effects of corona charging on lifetime sample wafers; a method that has earlier been used in the detection of Cu-LID. The results reveal that Cu-LID in solar cells can be recognized based on its relatively fast degradation rate and laterally heavy degradation patterns on extended defects. On the other hand, Cu-LID and another LID mechanism called Sponge-LID showed mutually similar properties, and further investigations possibly involving lifetime spectroscopic methods are necessary to clarify their relationship. The second objective of the thesis is to deepen the theoretical understanding of Cu-LID. Hence, a physical model based on a theory of electrostatically limited copper precipitation was derived, which together with a previously published Schottky junction model of metal precipitates enables the modeling of Cu-LID directly at the minority carrier lifetime level. Agreement between the model and experiments was obtained in most of the investigated cases. Consequently, the different material properties and environmental conditions that affect the strength of Cu-LID were identified. Theoretically, the strength of Cu-LID is mostly affected by the Cu and the doping concentrations, and the density of heterogeneous nucleation sites, all of which influence the final precipitate size that was found to reside between few to few tens of nanometers in radius. These results provide confirmation for the precipitation theory of Cu-LID, and provide insights for mitigating its effects in silicon devices.

AB - Copper is a common element in the environment and hence a difficult contaminant to control on silicon device manufacture lines. In p-type Si devices (e.g. solar cells), even very low copper concentrations can lead to copper-related light-induced degradation (Cu-LID), that is, degradation of the bulk minority carrier lifetime under excess carrier injection. As copper concentrations even below the detection limits of analytical methods can cause Cu-LID, it is necessary to identify its presence directly from device-level effects, which can be perturbed by the simultaneous occurrence of other light-induced degradation (LID) mechanisms. Hence, the first aim of this work is to clarify the properties of Cu-LID that enable its distinction from other LID mechanisms at the solar cell level. Thus, strong LID observed in industrial passivated emitter and rear contact (PERC) solar cells was characterized, and complemented with an analysis of the effects of corona charging on lifetime sample wafers; a method that has earlier been used in the detection of Cu-LID. The results reveal that Cu-LID in solar cells can be recognized based on its relatively fast degradation rate and laterally heavy degradation patterns on extended defects. On the other hand, Cu-LID and another LID mechanism called Sponge-LID showed mutually similar properties, and further investigations possibly involving lifetime spectroscopic methods are necessary to clarify their relationship. The second objective of the thesis is to deepen the theoretical understanding of Cu-LID. Hence, a physical model based on a theory of electrostatically limited copper precipitation was derived, which together with a previously published Schottky junction model of metal precipitates enables the modeling of Cu-LID directly at the minority carrier lifetime level. Agreement between the model and experiments was obtained in most of the investigated cases. Consequently, the different material properties and environmental conditions that affect the strength of Cu-LID were identified. Theoretically, the strength of Cu-LID is mostly affected by the Cu and the doping concentrations, and the density of heterogeneous nucleation sites, all of which influence the final precipitate size that was found to reside between few to few tens of nanometers in radius. These results provide confirmation for the precipitation theory of Cu-LID, and provide insights for mitigating its effects in silicon devices.

KW - silicon

KW - solar cell

KW - copper

KW - LID

KW - precipitation

KW - pii

KW - aurinkokenno

KW - kupari

KW - valodegradaatio

KW - erkautuminen

KW - silicon

KW - solar cell

KW - copper

KW - LID

KW - precipitation

M3 - Doctoral Thesis

SN - 978-952-60-7921-9

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

Light-induced degradation due to Cu precipitation in crystalline silicon: Modeling and impact on PERC solar cells

Abstrakti

Tutkimusalat

Pääsy asiakirjaan

Sormenjälki

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