Defect engineering in black silicon

Toni Pasanen

Defect engineering in black silicon

Julkaisun otsikon käännös: Kidevirheiden kontrollointi mustassa piissä

Toni Pasanen

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Musta pii, eli nanokuvioitu piin pinta, on tällä hetkellä aurinkokennoyhteisön suurena mielenkiinnon kohteena erinomaisten optisten ominaisuuksiensa ansiosta. Aurinkokennoihin liittyvä mustan piin tutkimus onkin aiemmin keskittynyt lähinnä heijastuksen ja pintarekombinaation vähentämiseen, ja nanokuvioitujen pintojen muut mahdolliset vaikutukset ovat jääneet vähemmälle huomiolle. Tässä väitöskirjassa laajennetaan mustan piin tutkimusaihetta käsittämään pintojen lisäksi myös ilmiöitä, joihin nanokuvioitu pinta vaikuttaa syvällä piikiekossa. Väitöskirjassa keskitytään ensin musta pii -pintoihin. Työssä osoitetaan, että märkäsyövytyksellä valmistetun mustan piin optisten ja sähköisten ominaisuuksien välillä ei tarvita kompromisseja, kun pinta passivoidaan atomikerroskasvatetulla (ALD) alumiinioksidilla (Al2O3). Yleisimpien kennorakenteiden etupinnalla on kuitenkin n-tyyppinen kerros, jonka passivointiin negatiivisia varauksia sisältävä Al2O3 ei sovellu hyvin. Ongelmaa lähestytään ALD SiO2/Al2O3 kaksoiskalvolla, jonka positiivisen varauksen avulla rekombinaatiota saadaan vähennettyä myös voimakkaasti seostetulla n-tyypin musta pii -pinnalla. Sen lisäksi, että korkea n-tyypin seostus hankaloittaa pinnan passivointia, työssä osoitetaan, että se myös kiihdyttää piin syöpymistä pesuliuoksissa. Nämä ilmiöt on huomioitava integroitaessa mustaa piitä korkean hyötysuhteen aurinkokennoihin. Toisena pääteemana työssä tutkitaan mustan piin vaikutusta syvällä piikiekossa tapahtuviin ilmiöihin. Mustan piin näytetään tehostavan haitallisten metalliepäpuhtauksien getterointia: rautakontaminoiduissa nanokuvioiduissa kiekoissa vähemmistövarauksenkuljettajien elinaika on getteroinnin jälkeen yli kolme kertaa niin suuri kuin vastaavissa kuvioimattomissa näytteissä (720 µs vs. 200 µs). Epäpuhtauksien getteroinnin lisäksi mustan piin näytetään vaikuttavan myös toiseen keskeiseen substraatissa tapahtuvaan ilmiöön: valaistuksen aiheuttamaan suorituskyvyn heikkenemiseen (LID). Valaisun aikana mustat monikiteiset kennot säilyttävät tehokkuutensa, kun taas perinteisesti kuvioidut kennot kärsivät voimakkaasta LID-ilmiöstä. Väitöskirjan tulokset osoittavat siten, että mustan piin edut eivät rajoitu vain erinomaisiin optisiin ominaisuuksiin. Lopuksi testataan kuivasyövytetyn mustan piin soveltuvuutta teollisiin monikiteisiin kennoihin ja paneeleihin. Hauraan nanorakenteen osoitetaan säilyvän ehjänä kenno- ja paneeliprosessoinnissa teollisilla valmistuslinjastoilla. Työssä valmistetut paneelit näyttävät tasaisen mustilta kaikkien prosessivaiheiden jälkeen. Lisäksi mustien paneelien näytetään säilyttävän suorituskykynsä 60° valon tulokulmaan asti, kun taas perinteiset paneelit alkavat menettää suorituskykyään jo 30° kallistuksen jälkeen. Tulokset siten vahvistavat, että mustan piin erinomaiset optiset ja sähköiset ominaisuudet säilyvät myös paneelitasolla.

Julkaisun otsikon käännös	Kidevirheiden kontrollointi mustassa piissä
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Savin, Hele, Vastuuprofessori
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-8748-1
Sähköinen ISBN	978-952-60-8749-8
Tila	Julkaistu - 2019
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

musta pii
aurinkokenno
pintapassivointi
getteronti
valodegradaatio

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-60-8749-8

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

Mustan piin matka laboratoriosta tuotantolinjastoille
Pasanen, T.
21/04/2020
1 kohde/ Medianäkyvyys
Lehdistö/media: Esiintyminen mediassa

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@phdthesis{76dad3a6f2fd434c8b333f9c5fbeae99,

title = "Defect engineering in black silicon",

abstract = "Black silicon (b-Si), i.e. a nanostructured silicon surface, is currently a subject of great interest within the photovoltaics (PV) community due to its excellent optics. While PV-related b-Si research has mainly focused on the reduction of reflectance and surface recombination, other possible effects of nanostructured surfaces have received less attention. This thesis investigates b-Si from a wider perspective and concentrates on engineering of surface and bulk defects in b-Si solar cells. The thesis first focuses on b-Si surfaces. It is demonstrated that no trade-offs are required between the optical and electrical properties of wet-chemically fabricated b-Si by the application of atomic-layer-deposited (ALD) aluminum oxide (Al2O3) surface passivation. The current mainstream solar cell architectures, however, have a phosphorus-doped emitter on the front, and thus, the negatively-charged Al2O3 is non-optimal. This work addresses the issue by using positively-charged ALD SiO2/Al2O3 stacks, which result in reduced recombination at diffused b-Si phosphorus emitter surfaces. In addition to affecting surface passivation, heavy phosphorus doping is shown to accelerate the consumption of silicon in standard cleaning solution, which strongly impacts both electrical and optical properties of b-Si emitters. All these results need to be considered in the design of high-efficiency b-Si solar cells. The second main theme of the work is engineering of bulk-related phenomena by b-Si. The nanostructures are shown to enhance gettering of detrimental metal impurities. Indeed, intentionally iron-contaminated b-Si wafers have more than three times higher minority carrier lifetime than polished samples after gettering (720 µs vs. 200 µs). In addition to impurity gettering, the impact of b-Si on another important bulk phenomenon, i.e., light-induced degradation (LID), is demonstrated. Black multicrystalline (mc-Si) passivated emitter and rear cells (PERC) show no or only slight degradation under illumination at elevated temperature, while standard acidic-textured equivalents suffer from severe LID. The increased gettering efficiency and reduced LID clearly demonstrate that benefits provided by b-Si are not limited only to the excellent optics. Finally, dry-etched b-Si is applied to industrial mc-Si PERC solar cells and modules. The fragile nanostructure is demonstrated to remain intact through cell and module fabrication at industrial production lines. Indeed, the prototype modules appear uniformly black after processing without anti-reflection coatings. Furthermore, the b-Si modules are shown to retain their performance until an incidence angle of 60°, whereas the modules with standard acidic-textured cells start to lose their performance already after a 30° tilt. Hence, the results demonstrate that the optical and electrical properties of b-Si can be maintained also at module level.",

keywords = "black silicon, solar cells, surface passivation, gettering, light-induced degradation, musta pii, aurinkokenno, pintapassivointi, getteronti, valodegradaatio, black silicon, solar cells, surface passivation, gettering, light-induced degradation",

author = "Toni Pasanen",

year = "2019",

language = "English",

isbn = "978-952-60-8748-1",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "181",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - Defect engineering in black silicon

AU - Pasanen, Toni

PY - 2019

Y1 - 2019

N2 - Black silicon (b-Si), i.e. a nanostructured silicon surface, is currently a subject of great interest within the photovoltaics (PV) community due to its excellent optics. While PV-related b-Si research has mainly focused on the reduction of reflectance and surface recombination, other possible effects of nanostructured surfaces have received less attention. This thesis investigates b-Si from a wider perspective and concentrates on engineering of surface and bulk defects in b-Si solar cells. The thesis first focuses on b-Si surfaces. It is demonstrated that no trade-offs are required between the optical and electrical properties of wet-chemically fabricated b-Si by the application of atomic-layer-deposited (ALD) aluminum oxide (Al2O3) surface passivation. The current mainstream solar cell architectures, however, have a phosphorus-doped emitter on the front, and thus, the negatively-charged Al2O3 is non-optimal. This work addresses the issue by using positively-charged ALD SiO2/Al2O3 stacks, which result in reduced recombination at diffused b-Si phosphorus emitter surfaces. In addition to affecting surface passivation, heavy phosphorus doping is shown to accelerate the consumption of silicon in standard cleaning solution, which strongly impacts both electrical and optical properties of b-Si emitters. All these results need to be considered in the design of high-efficiency b-Si solar cells. The second main theme of the work is engineering of bulk-related phenomena by b-Si. The nanostructures are shown to enhance gettering of detrimental metal impurities. Indeed, intentionally iron-contaminated b-Si wafers have more than three times higher minority carrier lifetime than polished samples after gettering (720 µs vs. 200 µs). In addition to impurity gettering, the impact of b-Si on another important bulk phenomenon, i.e., light-induced degradation (LID), is demonstrated. Black multicrystalline (mc-Si) passivated emitter and rear cells (PERC) show no or only slight degradation under illumination at elevated temperature, while standard acidic-textured equivalents suffer from severe LID. The increased gettering efficiency and reduced LID clearly demonstrate that benefits provided by b-Si are not limited only to the excellent optics. Finally, dry-etched b-Si is applied to industrial mc-Si PERC solar cells and modules. The fragile nanostructure is demonstrated to remain intact through cell and module fabrication at industrial production lines. Indeed, the prototype modules appear uniformly black after processing without anti-reflection coatings. Furthermore, the b-Si modules are shown to retain their performance until an incidence angle of 60°, whereas the modules with standard acidic-textured cells start to lose their performance already after a 30° tilt. Hence, the results demonstrate that the optical and electrical properties of b-Si can be maintained also at module level.

AB - Black silicon (b-Si), i.e. a nanostructured silicon surface, is currently a subject of great interest within the photovoltaics (PV) community due to its excellent optics. While PV-related b-Si research has mainly focused on the reduction of reflectance and surface recombination, other possible effects of nanostructured surfaces have received less attention. This thesis investigates b-Si from a wider perspective and concentrates on engineering of surface and bulk defects in b-Si solar cells. The thesis first focuses on b-Si surfaces. It is demonstrated that no trade-offs are required between the optical and electrical properties of wet-chemically fabricated b-Si by the application of atomic-layer-deposited (ALD) aluminum oxide (Al2O3) surface passivation. The current mainstream solar cell architectures, however, have a phosphorus-doped emitter on the front, and thus, the negatively-charged Al2O3 is non-optimal. This work addresses the issue by using positively-charged ALD SiO2/Al2O3 stacks, which result in reduced recombination at diffused b-Si phosphorus emitter surfaces. In addition to affecting surface passivation, heavy phosphorus doping is shown to accelerate the consumption of silicon in standard cleaning solution, which strongly impacts both electrical and optical properties of b-Si emitters. All these results need to be considered in the design of high-efficiency b-Si solar cells. The second main theme of the work is engineering of bulk-related phenomena by b-Si. The nanostructures are shown to enhance gettering of detrimental metal impurities. Indeed, intentionally iron-contaminated b-Si wafers have more than three times higher minority carrier lifetime than polished samples after gettering (720 µs vs. 200 µs). In addition to impurity gettering, the impact of b-Si on another important bulk phenomenon, i.e., light-induced degradation (LID), is demonstrated. Black multicrystalline (mc-Si) passivated emitter and rear cells (PERC) show no or only slight degradation under illumination at elevated temperature, while standard acidic-textured equivalents suffer from severe LID. The increased gettering efficiency and reduced LID clearly demonstrate that benefits provided by b-Si are not limited only to the excellent optics. Finally, dry-etched b-Si is applied to industrial mc-Si PERC solar cells and modules. The fragile nanostructure is demonstrated to remain intact through cell and module fabrication at industrial production lines. Indeed, the prototype modules appear uniformly black after processing without anti-reflection coatings. Furthermore, the b-Si modules are shown to retain their performance until an incidence angle of 60°, whereas the modules with standard acidic-textured cells start to lose their performance already after a 30° tilt. Hence, the results demonstrate that the optical and electrical properties of b-Si can be maintained also at module level.

KW - black silicon

KW - solar cells

KW - surface passivation

KW - gettering

KW - light-induced degradation

KW - musta pii

KW - aurinkokenno

KW - pintapassivointi

KW - getteronti

KW - valodegradaatio

KW - black silicon

KW - solar cells

KW - surface passivation

KW - gettering

KW - light-induced degradation

M3 - Doctoral Thesis

SN - 978-952-60-8748-1

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

Defect engineering in black silicon

Abstrakti

Tutkimusalat

Pääsy asiakirjaan

Sormenjälki

Laitteet

OtaNano

OtaNano Nanofab

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