Carrier Lifetime Limitation of Industrial Ga-Doped Cz-Grown Silicon After Different Solar Cell Process Flows

Post, Regina; Niewelt, Tim; Kwapil, Wolfram; Schubert, Martin C.

doi:10.1109/jphotov.2021.3116017

Cited by 9 publications

(14 citation statements)

References 41 publications

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“…This is particularly important as the industry rapidly shifts from boron to gallium as the main dopant agent for p-type silicon. It is of great importance to identify the defect(s) responsible for lifetime instabilities recently observed in solar cells fabricated with p-type Ga-doped c-Si wafers, [119][120][121][122] as these wafers have the potential to enable a next-generation of high-efficiency silicon solar cells based on p-type c-Si wafers.…”

Section: Final Thoughtsmentioning

confidence: 99%

Silicon Heterojunction Solar Cells and p‐type Crystalline Silicon Wafers: A Historical Perspective

et al. 2022

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The first reports of both boron–oxygen (BO)‐related light‐induced degradation (BO‐LID) and amorphous/crystalline silicon heterojunction (SHJ) solar cell fabrication date back to the early 1970s. However, the complete development of the “modern” SHJ structure took place well before BO defect stabilization processes were developed. Due to the susceptibility of p‐type Czochralski (Cz)‐grown silicon to BO‐LID, such wafers were deemed unsuitable for SHJ solar cells. In addition to stability issues, lower charge carrier lifetimes due to contamination and challenges with surface passivation posed barriers to the adoption of p‐type wafers in SHJ applications. Herein, these three key challenges are discussed in detail. Kinetic modeling and experimental results reveal the severe impact of BO‐LID in p‐type SHJ solar cells and provide possible explanations as to why earlier attempts using p‐type wafers might have failed. The role of gettering and advanced hydrogenation in stabilizing BO defects in SHJ solar cells is demonstrated experimentally. Finally, a summary of the effective surface recombination velocities reported in the literature for hydrogenated intrinsic amorphous silicon passivation of p‐ and n‐type crystalline silicon wafers is presented. Based on these findings, the potential of p‐type wafers to enable a next‐generation of high‐efficiency solar cells featuring carrier‐selective contacts is discussed.

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Section: Final Thoughtsmentioning

confidence: 99%

Silicon Heterojunction Solar Cells and p‐type Crystalline Silicon Wafers: A Historical Perspective

et al. 2022

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“…However, silicon wafers used in mass production generally have lower carrier lifetimes than those reported in refs. [18, 19] and the bulk Fe concentrations are likely higher. Moreover, additional contamination likely occurs during cell processing, which is difficult to quantify or generalize.…”

Section: Resultsmentioning

confidence: 99%

“…Some have reported a low bulk Fe concentration on the order of 10 9 cm −3 in state-of-the-art high-quality gallium doped Cz-Si wafers. [18,19] According to the simulation in Figure 6B, these high-quality wafers may not necessarily need very effective gettering to achieve 25% cell efficiency. However, silicon wafers used in mass production generally have lower carrier lifetimes than those reported in refs.…”

Section: Impact Of the Oxide Blocking Effects In A Typical Poly-si/si...mentioning

confidence: 99%

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Impurity Gettering in Polycrystalline‐Silicon Based Passivating Contacts—The Role of Oxide Stoichiometry and Pinholes

Yang

Krügener

Feldmann

et al. 2022

Advanced Energy Materials

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Polycrystalline‐silicon/oxide (poly‐Si/SiOx) passivating contacts for high efficiency solar cells exhibit excellent surface passivation, carrier selectivity, and impurity gettering effects. However, the ultrathin SiOx interlayer can act as a diffusion barrier for metal impurities and this potentially slows down the overall gettering rate of the poly‐Si/SiOx structures. Herein, the factors that determine the blocking effects of the SiOx interlayers are identified and investigated by examining two general types of the SiOx interlayers: 1.3 nm ultrathin tunneling SiOx with negligible pinholes and 2.5 nm SiOx with thermally created pinholes. Iron is used as tracer impurity in silicon to quantify the gettering rate. By fitting the experimental gettering kinetics by a diffusion‐limited segregation gettering model, the blocking effects of the SiOx interlayers are quantified by a transport parameter. Both the oxide stoichiometry and pinhole density affect the effective transport of iron through SiOx interlayers. The oxide stoichiometry depends strongly on the oxidation method, while the pinhole density is affected by the activation temperature, doping concentration, doping technique, and possibly the dopant type as well. To enable a fast gettering process during typical high‐temperature formation of the poly‐Si/SiOx structures, a SiOx interlayer that is less stoichiometric or with a higher pinhole density is preferred.

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“…The silicon photovoltaic (PV) industry has recently moved away from boron (B) and transitioned to gallium (Ga) as the main dopant element for p-type Czochralski-grown silicon (Cz-Si) wafers, primarily to avoid the well-known boron-oxygen defect. [1,2] Although several articles have reported higher effective minority carrier lifetimes in Ga-doped wafers than in B-doped wafers, [3][4][5][6][7] detailed studies of the material quality of industrial Ga-doped ingots are still rather limited. Recently, Horzel et al [7] reported effective lifetimes in the range of 3-17 ms along a customgrown Ga-doped Cz ingot with a resistivity range of 5-12 Ω cm.…”

Section: Introductionmentioning

confidence: 99%

Investigating Wafer Quality in Industrial Czochralski‐Grown Gallium‐Doped p‐Type Silicon Ingots with Melt Recharging

Basnet

Sun²,

et al. 2023

Solar RRL

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Herein, a systematic study of the electronic quality of gallium‐doped p‐type silicon wafers from Czochralski‐grown ingots with melt recharging is presented. It is found that in the as‐grown state, the ingots contain interstitial iron concentrations in the range of 3 × 109–2 × 1010 cm−3, with a trend of slightly higher concentrations toward the tail end of each ingot, and in subsequently grown ingots. However, analysis of the effective lifetimes indicates that iron–gallium pairs are not the dominant recombination centers in the as‐grown state. Moreover, when these wafers are subjected to a tabula rasa step, an increase in the iron concentration is observed in the range of 1 × 1010–6 × 1010 cm−3, with iron–gallium pairs becoming the dominant recombination centers. This is possibly caused by the dissolution of pre‐existing precipitated iron in the wafers. Nevertheless, the negative impact of iron contamination can be dramatically reduced by subjecting the wafers to a phosphorus diffusion gettering step, as is commonly incorporated in the fabrication of p‐type passivated emitter and rear cells. Therefore, it is concluded that the quality of the ingots is not limited by iron contamination, even after multiple ingots are pulled from the recharged melt.

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Carrier Lifetime Limitation of Industrial Ga-Doped Cz-Grown Silicon After Different Solar Cell Process Flows

Cited by 9 publications

References 41 publications

Silicon Heterojunction Solar Cells and p‐type Crystalline Silicon Wafers: A Historical Perspective

Silicon Heterojunction Solar Cells and p‐type Crystalline Silicon Wafers: A Historical Perspective

Impurity Gettering in Polycrystalline‐Silicon Based Passivating Contacts—The Role of Oxide Stoichiometry and Pinholes

Investigating Wafer Quality in Industrial Czochralski‐Grown Gallium‐Doped p‐Type Silicon Ingots with Melt Recharging

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