TY - JOUR

T1 - Impact of Fast-Firing Conditions on Light- and Elevated-Temperature-Induced Degradation (LeTID) in Ga-Doped Cz-Si

AU - Winter, Michael

AU - Walter, Dominic C.

AU - Schmidt, Jan

PY - 2023/8/30

Y1 - 2023/8/30

N2 - The fast-firing step commonly applied at the end of solar cell production lines triggers 'Light- and elevated-Temperature-Induced Degradation' (LeTID) effects of the carrier lifetime in Ga-doped Cz-Si wafers and solar cells made thereof. As far as the defect formation within the silicon bulk is concerned, the key parameters of the fast-firing step are the peak firing temperature (FT) and the band velocity vband of the conveyor belt, where the latter mainly defines the cooling ramp after the firing peak. In this contribution, we show that the extent of LeTID and the dependence on the applied temperature during degradation increase strongly with increasing measured FT (from 680 °C to 800 °C), vband (from 2.8 to 7.2 m/min), and the refractive index n of the hydrogen-rich silicon nitride layer deposited on the wafer surfaces (from 2.07 to 2.37). Through temperature-dependent degradation experiments, we determine an activation energy of EA = (0.55 ± 0.10) eV of the LeTID mechanism in Ga-doped Cz-Si, which is independent of FT and vband. From this observation we conclude that a single defect activation mechanism is most likely responsible for the examined LeTID effect, independent of the firing conditions. However, the concentration of recombination-active defect centers after LeTID depends critically on FT, vband, and n, which we attribute to variations of the in-diffused hydrogen concentrations from the silicon nitride layers during firing. Our experiments hence point towards an involvement of hydrogen in the LeTID mechanism observed in Ga-doped Cz-Si.

AB - The fast-firing step commonly applied at the end of solar cell production lines triggers 'Light- and elevated-Temperature-Induced Degradation' (LeTID) effects of the carrier lifetime in Ga-doped Cz-Si wafers and solar cells made thereof. As far as the defect formation within the silicon bulk is concerned, the key parameters of the fast-firing step are the peak firing temperature (FT) and the band velocity vband of the conveyor belt, where the latter mainly defines the cooling ramp after the firing peak. In this contribution, we show that the extent of LeTID and the dependence on the applied temperature during degradation increase strongly with increasing measured FT (from 680 °C to 800 °C), vband (from 2.8 to 7.2 m/min), and the refractive index n of the hydrogen-rich silicon nitride layer deposited on the wafer surfaces (from 2.07 to 2.37). Through temperature-dependent degradation experiments, we determine an activation energy of EA = (0.55 ± 0.10) eV of the LeTID mechanism in Ga-doped Cz-Si, which is independent of FT and vband. From this observation we conclude that a single defect activation mechanism is most likely responsible for the examined LeTID effect, independent of the firing conditions. However, the concentration of recombination-active defect centers after LeTID depends critically on FT, vband, and n, which we attribute to variations of the in-diffused hydrogen concentrations from the silicon nitride layers during firing. Our experiments hence point towards an involvement of hydrogen in the LeTID mechanism observed in Ga-doped Cz-Si.

KW - Carrier lifetime

KW - degradation

KW - gallium

KW - LID

KW - light- and elevated-temperature-induced degradation (LeTID)

KW - silicon

UR - http://www.scopus.com/inward/record.url?scp=85169707023&partnerID=8YFLogxK

U2 - 10.1109/JPHOTOV.2023.3304118

DO - 10.1109/JPHOTOV.2023.3304118

M3 - Article

AN - SCOPUS:85169707023

VL - 13

SP - 849

EP - 857

JO - IEEE journal of photovoltaics

JF - IEEE journal of photovoltaics

SN - 2156-3381

IS - 6

ER -