Investigation of light-induced degradation in N-Type silicon heterojunction solar cells during illuminated annealing at elevated temperatures

Soeriyadi

et al. 2022

IEEE J. Photovoltaics

Self Cite

Here, we demonstrate the effectiveness of illuminated annealing using high-intensity light to improve the efficiency of industrial n-type silicon heterojunction (SHJ) solar cells. The application of high intensity laser light during annealing at 200 °C led to efficiency improvements as large as 0.7% abs and final efficiencies as high as 24.5%. This was demonstrated on industrial SHJ solar cells from five different manufacturers, indicating the robust application of this technique. We show that the annealing process with high-intensity light leads to significant efficiency enhancements compared to previous observations using light soaking under 1-sun conditions, meaning the process can be completed in 30 s, rather than hours. The observed enhancements were related to increased V OC and fill factor. If this approach can be tailored to time scales amenable with mass production, the associated efficiency enhancements could drive reductions in the levelized cost of electricity for SHJ solar cells, making them more competitive in the face of existing technologies.

Section: Resultsmentioning

confidence: 86%

High-Intensity Illuminated Annealing of Industrial SHJ Solar Cells: A Pilot Study

Soeriyadi

et al. 2022

IEEE J. Photovoltaics

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“…A recent report by Madumelu et al shed some light on the intricacies of light-induced changes in SHJ cell performance. [72,73] By investigating a wide variety of illuminated annealing conditions on commercially produced n-type SHJ cells, they showed that, depending on the temperature and illumination intensity, the cells can undergo significant degradation. Dark annealing at 160 C led to an efficiency improvement of 0.2 AE 0.1% abs ; however, annealing under 1 sun illumination caused a reduction in efficiency of 0.5% abs AE 0.3% abs , with a maximum degradation of 0.8% abs .…”

Section: Post-cell Illuminated Annealingmentioning

confidence: 99%

“…Comparison of efficiency for industrial n-type SHJ solar cells that were either light soaked under 1 sun illumination at 160 C or dark annealed at 160 C. A reference sample that was not exposed to light or heat is also shown. Reproduced with permission [72]. Copyright 2020, Elsevier.…”

mentioning

confidence: 99%

Progress with Defect Engineering in Silicon Heterojunction Solar Cells

Physica Rapid Research Ltrs

Stefani

Soeriyadi

et al. 2021

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Silicon heterojunction (SHJ) solar cells are formed by the deposition of stacks of intrinsic and doped hydrogenated amorphous silicon layers (a-Si:H) on the surface of crystalline silicon (c-Si) wafers. [1][2][3] The doped a-Si:H layers determine the carrier selectivity of each contact, which defines the direction of current flow, and the intrinsic a-Si:H layers, which are deposited directly onto the crystalline silicon (c-Si) surface, provide excellent surface passivation. [4,5] The cells are completed by the deposition of a transparent conducting oxide (TCO) to aid lateral conduction and the formation of metal contacts, typically by screen printing of silver. [6][7][8] This technology was pioneered in the 1990s by Japanese company Sanyo. [9][10][11] The solar photovoltaics (PV) market is currently dominated by the passivated emitter and rear cell (PERC) design. [12,13] Compared to PERC, SHJ solar cells have multiple advantages. They have demonstrated higher open circuit voltages (V OC ), with V OC values as high as 750 mV. [9] The high V OC is related to the excellent surface passivation provided by the a-Si:H layers. The world record 1 sun efficiency of 26.7% for a single-junction silicon solar cell was achieved using this approach, [14] and cells with efficiency exceeding 25% have been fabricated in an industrial environment. [15] Another advantage of SHJ cells, which is linked to the high V OC , is the lower temperature coefficient, meaning that power losses in SHJ cells operated at elevated temperatures are lower than in other siliconbased technologies. [2,16] Therefore, under realistic cell-operation conditions in the field, the actual power output of an SHJ module will be higher than that of a PERC module, even if they have the same power rating at room temperature. In addition, the expected rise of tandem solar cells with silicon as the bottom cell has also increased interest in the SHJ technology, as it is well suited as the bottom cell in a tandem device. [17][18][19][20][21][22] These advantages mean that industry is seriously looking into SHJ solar cells as a technology to compete with PERC in the future. The ITRPV 11th edition indicates that the market share for SHJ cells is expected to increase to 15% over the next ten years [23] which will represent a significant volume as we move toward terawatt-scale photovoltaics. [24] One unique aspect of SHJ cells is that all processing occurs in a low-temperature regime, typically <250 C. [4,16,25] This is very different to most other cell architectures, such as aluminium

“…Thus, understanding the longterm stability of SHJ solar cells is imperative. To date, several studies [19][20][21] have been conducted to investigate the stability…”

mentioning

confidence: 99%

“…The results suggested that, to some extent, degradation had occurred in the SHJ modules, i.e., the peak power decay was 0.36% per year. Madumelu et al [20] reported that SHJ solar cells underwent a temperature-dependent degradation process, in which the extent of degradation increased with increasing temperatures. Another important phenomenon observed was that a recovery in the efficiency (η) of the SHJ solar cells occurred during subsequent illumination at 160°C, which could be accelerated by increasing the illumination intensity.…”

mentioning

confidence: 99%

Light soaking-induced performance enhancement in a-Si:H/c-Si heterojunction solar cells

et al. 2022

Sci. China Mater.

Intrinsic hydrogenated amorphous silicon (a-Si:H) film has been demonstrated to hydrogenate dangling bonds on the surface of crystalline silicon (c-Si), which reduces the interface defect density, thus enabling an outstanding passivation effect [1-3]. However, like many other industrial c-Si solar cells that suffer from light-induced degradation and light and elevated temperature induced degradation (LeTID) [4,5], the decay of electrical properties has also been found in thin-film a-Si:H solar cells [6][7][8], as well as samples of c-Si coated with intrinsic a-Si:H films after light soaking [9]. A significant observation reported by Plagwitz et al. [10] suggested that illumination induced an increase in surface recombination velocities for both a-Si:H coated p-type and n-type c-Si substrates. The degradation of performance is generally attributed to the generation of deeplevel defects acting as recombination centers, most likely as single dangling bonds [11,12], which is considered to be related to the Staebler-Wronski effect (SWE) [13].However, when a-Si:H film is doped and overlays with another thin intrinsic a-Si:H film (Fig. S1), the functionality of silicon heterojunction (SHJ) cells can be further increased because of the carrier selectivity possessed by the n-type and ptype a-Si:H overlayers, which efficiently help to collect electrons and holes, respectively [14,15]. Such a structure of c-Si coated with doped/intrinsic a-Si:H bilayers is the key component of SHJ solar cells. Compared with the high fabrication temperature of conventional c-Si solar cells (up to 900°C), SHJ solar cells usually require a relatively low processing temperature (<200°C) when a-Si:H is deposited using plasma-enhanced chemical vapor deposition (PECVD) [16,17]. Due to the simple and low-cost manufacturing process, as well as its excellent passivation effect, the a-Si:H film has been widely used in SHJ solar cells. Tanaka et al. [17] proposed the p-a-Si:H/n-c-Si heterojunction structure with a thin intrinsic a-Si:H layer inserted in between, which achieved an efficiency (η) of 18.1% in 1992. Recently, Sai et al. [18] improved the open-circuit voltage (V OC ) of SHJ solar cells to 754 mV, and LONGi solar reported an η of 26.3% in 2021 (https://www.longi.com/cn/news/7093/).It is essential for solar cells to maintain their excellent properties during long periods of light soaking, which occurs in a normal working environment. Thus, understanding the longterm stability of SHJ solar cells is imperative. To date, several studies [19][20][21] have been conducted to investigate the stability