New insights on LeTID/BO-LID in p-type mono-crystalline silicon

Lin, Dongyang; Hu, Zechen; He, Qiyuan; Yang, Deren; Song, Lihui; Yu, Xuegong

doi:10.1016/j.solmat.2021.111085

“…From the results, we can also hypothesize that some LeTID defects already existed in silicon bulk just after the cofiring process. In literature, Lin et al [12] found that %25% light-induced degradation (LID) already existed in crystalline silicon after the firing and before the postfiring treatment, which supported our hypothesis. Subsequently, the first-step bias treatment is able to regenerate the preexisting LeTID defect and results in an enhancement of bulk lifetime of gallium-doped silicon.…”

Section: Introductionsupporting

confidence: 88%

“…Finally, this treatment should enable these cells in the complete regenerated state and therefore enhance the performance of these PERC solar cells, which is consistent with our experimental results in Figure 2. As the V oc of the cells is improved, it indicates that some LeTID defect might already exist after the cofiring process, and this phenomenon is also observed by Lin et al [12] . More information on LeTID can also be found in the review paper.…”

Section: Discussionsupporting

confidence: 72%

Performance Improvement of Gallium‐Doped Passivated Emitter and Rear Cells by Two‐Step Bias Application

Song

¹

,

Hu

²

,

Fang

³

et al. 2021

Self Cite

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Passivated emitter and rear cell (PERC) solar cells have dominated the photovoltaic market in recent years. Continuously improving the efficiency of PERC solar cells is of great importance to enable the goal of low electricity cost, which is cheaper than the cost of thermal power generation. Herein, it is demonstrated that a two‐step postfiring bias treatment is able to evidently enhance the efficiency of commercial gallium‐doped PERC solar cells by up to 0.1% absolute. In detail, the first‐step bias treatment is done by forward biasing the PERC solar cells at 12 A and 200 °C for 60 min, resulting in an average efficiency enhancement at around 0.05% absolute. The second‐step bias treatment is done by reverse biasing the PERC solar cells at −0.1 or −0.2 V and at the elevated temperatures for certain times, leading to another average efficiency enhancement at around 0.05% absolute. To explore the mechanism underlying the two‐step bias treatments on improving cell efficiency, a new model in light of hydrogen behavior under electric field is proposed to explain this phenomenon.

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“…By using the method given by ref. [33] for judging whether the as-used illuminated annealing conditions can activate LeTID defects, we measured the IDLS (Injection-Dependent Lifetime Spectra) curves of five groups of lifetime samples made from same position of silicon wafers as five groups of PERC solar cells by using a WCT-120 equipment after sintering, dark annealing at 200 °C for 30 min, and regeneration at 100 °C and 1 sun for 24 h. It should be mentioned that the lifetime samples were prepared by the fabrication process of PERC solar cells without the steps of phosphorus diffusion, removing PSG, laser grooving on the back passivation layer, and screen printing front and back electrodes. In order to avoid the influence of Fe i + on the measurement results, all the samples were kept in the dark at room temperature for 3 h before each of the IDLS measurements to make most of Fe i + in the samples change into Fe-B pairs.…”

Section: Perc Solar Cellsmentioning

confidence: 99%

In Situ LID and Regeneration of PERC Solar Cells from Different Positions of a B-Doped Cz-Si Ingot

Yuan

¹

,

Ding

²

,

Ai

³

et al. 2022

International Journal of Photoenergy

3

0

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In order to investigate the light-induced-degradation (LID) and regeneration of industrial PERC solar cells made from different positions of silicon wafers in a silicon ingot, five groups of silicon wafers were cut from a commercial solar-grade boron-doped Czochralski silicon (Cz-Si) ingot from top to bottom with a certain distance and made into PERC solar cells by using the standard industrial process after measuring lifetimes of minority carriers and concentrations of boron, oxygen, carbon, and transition metal impurities. Then, the changes of their I - V characteristic parameters (efficiency η , open-circuit voltage V oc , short-circuit current I sc , and fill factor FF ) with time were in situ measured by using a solar cell I - V tester during the 1st LID (45°C, 1 sun, 12 h), regeneration (100°C, 1 sun, 24 h), and 2nd LID (45°C, 1 sun, 12 h). The results show that the LID and regeneration of the PERC solar cells are caused by the transition of B-O defects playing a dominant role together with the dissociation of Fe-B pairs playing a secondary role. The decay of η during the 1st LID is caused by the degradation of V oc , I sc , and FF , while the increase of η during the regeneration is mainly contributed by V oc and FF , and the decay of η during the 2nd LID is mainly induced by the degradation of I sc . After regeneration, the decay rate of η reduces from 4.43%–5.56% (relative) during the 1st LID to 0.33%–1.75% (relative) during the 2nd LID.

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“…These degradations have shown to be more significant in the PERC technology. PERC technology improved the efficiency of the existing solar cells, enabling efficiency levels of 21-24% without a significant increase in price [87]. In PERC p-type multi-crystalline silicon cells, the effect of LID can cause a reduction in the power output of the module at the maximum power point (MPP) by around 10% [88,89].…”

Section: Light Induced Degradationmentioning

confidence: 99%

Review on the Sources of Power Loss in Monofacial and Bifacial Photovoltaic Technologies

Silva

¹

,

Gul

²

,

Chaudhry

³

2021

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An evaluation of the degradation effects on photovoltaic modules is essential to minimise uncertainties in the system operation. Bifacial photovoltaic technology is attracting attention due to the capacity of generating energy from the front and rear sides. This paper presents a review of degradation factors, for both conventional monofacial and bifacial photovoltaic modules, to highlight how the current and voltage characteristics of these technologies are affected by degradation. Microcracking, encapsulant discoloration, and light induced degradation seem to have similar effects on both modules. Contrarily, bifacial modules are more prone to potential induced degradation as the electromagnetic shielding is affected by the bifaciality. Bifacial devices are less affected by light and elevated temperature induced degradation. The degradation (1.3%) is similar for both technologies, up to 40 kWh/m2 of solar radiation. Above this value, monofacial degradation increases faster, reaching values of 7%. For tilted systems, the front side soiling degradation of 0.30% per day is similar for both technologies. For vertical systems, soiling loss for bifacial is considerably lower with values of 0.02% per day.

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“…Since wafers grown by the VGF technique contain little oxygen and thus show little boron–oxygen (BO) related light‐induced degradation (BO‐LID), LeTID is typically the dominating degradation effect. The exact defect which is causing LeTID is still unknown, and there are different models to describe it 7‐10 . However, all cited models agreed that hydrogen plays some role in the defect formation.…”

Section: Introductionmentioning

confidence: 99%

LeTID mitigation via an adapted firing process in p‐type PERC cells from SMART cast‐monocrystalline, Czochralski and high‐performance multicrystalline silicon

Maischner

¹

,

Maus

²

,

Greulich

³

et al. 2021

Progress in Photovoltaics

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In this work, we analyse passivated emitter and rear cells (PERC), based on wafers made from seed manipulation for artificially controlled defects technique (SMART) monocrystalline silicon, magnetically grown and conventional Czochralski (mCz and Cz) silicon, and high‐performance multicrystalline (hpm) silicon. All wafers were processed identically except for the hpm wafers, which received an acidic texture instead of random pyramids. The energy conversion efficiency η of the SMART cells of 21.4 % is similar to the mCz cells (21.5 %) while being more than 1.90.1em%abs higher than for the hpm cells. Furthermore, we here show for the first time that light‐ and elevated temperature‐induced degradation (LeTID) is mitigated in hpm, Cz and SMART PERC cells without significant losses in initial efficiency by an adapted fast‐firing process, incorporating slower firing ramps that can be used in industrial production. The cells that are fired with these ramps show no significant efficiency loss ( 10.1em%rel

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New insights on LeTID/BO-LID in p-type mono-crystalline silicon

Cited by 13 publications

References 39 publications

Performance Improvement of Gallium‐Doped Passivated Emitter and Rear Cells by Two‐Step Bias Application

In Situ LID and Regeneration of PERC Solar Cells from Different Positions of a B-Doped Cz-Si Ingot

Review on the Sources of Power Loss in Monofacial and Bifacial Photovoltaic Technologies

LeTID mitigation via an adapted firing process in p‐type PERC cells from SMART cast‐monocrystalline, Czochralski and high‐performance multicrystalline silicon

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