A novel passivating electron contact for high-performance silicon solar cells by ALD Al-doped TiO2

Liu, Ying; Sang, Borong; Hossain, Md. Anower; Gao, Kun; Cheng, Hao; Song, Xiaomin; Zhong, Sihua; Shi, Linxing; Shen, Wei; Hoex, Bram; Huang, Z. G.

doi:10.1016/j.solener.2021.09.083

Cited by 31 publications

(33 citation statements)

References 33 publications

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“…Furthermore, wide-bandgap materials are also beneficial in realizing the large asymmetry between electron and hole conductivity, thus realizing superior charge carrier selectivity. [2] Up to now, a lot of metal compounds, such as metal oxides, [10][11][12][13] fluorides, [14][15][16] nitrides, and oxynitride, [17][18][19] have been reported as efficient electron transport layers for c-Si solar cells. They typically have a small conduction band offset (ΔE C ) and large valance band offset (ΔE V ) with c-Si.…”

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Perovskite‐Based Electron‐Selective Contacts for Silicon Solar Cells

et al. 2022

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Efficient carrier-selective contacts play significant roles in highperformance solar cells, which are responsible for the separation and collection of photogenerated charge carriers. Electronselective contacts only collect electrons and block holes, while hole-selective contacts are opposite. It is believed that the large asymmetry between electron and hole conductivity, together with a suitable band offset, is the key to realize efficient carrierselective contacts. [1,2] To date, all of the mainstream commercial crystalline silicon (c-Si) solar cells, that is, passivated emitter and rear cell (PERC) cells, [3] tunnel oxide passivating contact (TPOCon) cells, [4] and heterojunction with intrinsic thin layer (HIT) cells, [5] utilize either heavily doped c-Si films, poly-Si films, or amorphous Si films as carrier-selective contacts. Although they are efficient, any heavily doped Si suffers from parasitic optical absorption, due to their narrow bandgaps (<2 eV). Moreover, heavy doping also induces Auger recombination in PERC solar cells, which further limit the power conversion efficiency (PCE). [6] From manufacturing aspects, the heavy doping in silicon is either achieved by high-temperature diffusion (e.g., >800 °C for PERC cells and TOPCon cells) or relies on capital-intensive equipment (e.g., plasmaenhanced chemical vapor deposition [PECVD] for HIT cells).These disadvantages have sparked intensive exploration of dopant-free carrierselective materials to replace heavily doped Si thin layers. They feature nonsilicon materials with wide bandgap and high or low workfunction (WF). [6][7][8][9] Using the dopant-free contacts, it is expected to reduce the parasitic optical absorption and simplify the fabrication process as well as lower the cost. Furthermore, wide-bandgap materials are also beneficial in realizing the large asymmetry between electron and hole conductivity, thus realizing superior charge carrier selectivity. [2] Up to now, a lot of metal compounds, such as metal oxides, [10][11][12][13] fluorides, [14][15][16] nitrides, and oxynitride, [17][18][19] have been reported as efficient electron transport layers for c-Si solar cells. They typically have a small conduction band offset (ΔE C ) and large valance band offset (ΔE V ) with c-Si. Combining with low-WF metals, they can form excellent ihmic contacts with c-Si, making photogenerated electrons collected efficiently.Despite the successful demonstration of carrier selectivity, it is widely accepted that environmental and thermal stability remains one of the challenges for dopant-free contacts to be considered for industrial adoption. [20][21][22][23][24] A lot of dopant-free contacts are found to be sensitive to air exposure, especially when combined with heating, leading to the degradation of solar cell performance. [24][25][26][27][28][29] For example, ρ c of KF x /Al and CsF x /Al increase by more than one order of magnitude when exposed to air for 1000 h. [14] Furthermore, the V OC and FF of the c-Si solar cell using ZnO/LiF/Al as the electron-selecti...

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Perovskite‐Based Electron‐Selective Contacts for Silicon Solar Cells

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“…In a separate work, Liu et al varied the Al:Ti cycle ratio to form Al‐doped TiO 2 films, obtaining an effective minority carrier lifetime τ eff of 1.9 ms and contact resistivity ρ c of 100 mΩ cm 2 on Si using an optimized Al 0.20 Ti 0.36 O layer with LiF/Al contacts, after annealing at 300 °C. [ 14 ] Although doping with aluminum was found to improve surface passivation quality and reduce contact resistivity in this case, the obtained contact resistivity was still relatively high (100 mΩ cm 2 ). In addition, we believe that the use of the transmission line measurement (TLM) method to measure contact resistivity makes the obtained contact resistivity values unreliable due to the high film thickness (16.5 nm).…”

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confidence: 96%

Outstanding Surface Passivation for Highly Efficient Silicon Solar Cells Enabled by Innovative Al_yTiO_x/TiO_xElectron‐Selective Contact Stack

et al. 2022

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Passivating contacts based on transition metal oxides (TMOs) have the potential to overcome existing performance limitations in high‐efficiency crystalline silicon (c‐Si) solar cells, which is a significant driver for continuing cost/Watt reductions of photovoltaic electricity. Herein, innovative stacks of Al‐alloyed TiO x (Al y TiO x ) and pure TiO x as transparent electron‐selective passivating contacts for n‐type c‐Si surfaces are explored. An optimized stack of 2 nm Al y TiO x and 2 nm TiO x is shown to provide both record‐quality surface passivation and excellent electrical contact, with a surface recombination current density prefactor J 0 of 2.4 fA cm−2 and a specific contact resistivity ρ c of 15.2 mΩ cm2. The performance of this innovative stack significantly exceeds previously reported values for pure or doped TiO x single layers, SiO x /TiO x stacks, a‐Si:H/TiO x stacks, and other transparent contact technologies. Furthermore, an excellent efficiency of 21.9% is attained by incorporating the optimized stack as a full‐area rear contact in an n‐type c‐Si solar cell. The findings set a new benchmark for the passivation performance of metal oxide‐based passivating contacts, bringing it to a level on par with state‐of‐the‐art SiO x /poly‐Si contacts while greatly improving optical transparency.

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“…In this context, even for silicon technology that has been studied since the 1950s, new approaches with selective contacts for electron or holes are being developed. [6][7][8][9][10] To understand the impact of interface properties, researchers combine information from different characterization techniques, each one with its merits and limitations. Examples include microscopy techniques such as scanning and transmission electron microscopy, for morphology, Raman spectroscopy and As devices become smaller and more complex, the interfaces between adjacent materials become increasingly important and are often critical to device performance.…”

Section: Introductionmentioning

confidence: 99%

“…In this context, even for silicon technology that has been studied since the 1950s, new approaches with selective contacts for electron or holes are being developed. [ 6–10 ] To understand the impact of interface properties, researchers combine information from different characterization techniques, each one with its merits and limitations. Examples include microscopy techniques such as scanning and transmission electron microscopy, for morphology, Raman spectroscopy and grazing incident angle X‐ray diffraction, for structure, time resolved photoluminescence and admittance electrical measurements, for charge carrier dynamics, X‐ray photoelectron spectroscopy, and secondary‐ion mass spectrometry, for composition, among others, where of course, final devices are the ultimate tool for performance evaluation.…”

Section: Introductionmentioning

confidence: 99%

Characterization of the Interfacial Defect Layer in Chalcopyrite Solar Cells by Depth‐Resolved Muon Spin Spectroscopy

Alberto

Vilão

Ribeiro

et al. 2022

Adv Materials Inter

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As devices become smaller and more complex, the interfaces between adjacent materials become increasingly important and are often critical to device performance. An important research goal is to improve the interface between the absorber and the window layer by inserting buffer layers to adjust the transition. Depth‐resolved studies are key for a fundamental understanding of the interface. In the present experiment, the interface between the chalcopyrite Cu(In,Ga)Se2 absorber and various buffer layers are investigated using low‐energy muon spin rotation (μSR) spectroscopy. Depth resolution in the nm range is achieved by implanting the muons with different energies so that they stop at different depths in the sample. Near the interface, a region about 50 nm wide is detected where the lattice is more distorted than further inside the absorber. The distortion is attributed to the long‐range strain field caused by defects. These measurements allow a quantification of the corresponding passivation effect of the buffer layer. Bath‐deposited cadmium sulfide provides the best defect passivation in the near interface region, in contrast to the dry‐deposited oxides, which have a much smaller effect. The experiment demonstrates the great potential of low energy μSR spectroscopy for microscopic interfacial studies of multilayer systems.

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A novel passivating electron contact for high-performance silicon solar cells by ALD Al-doped TiO2

Cited by 31 publications

References 33 publications

Perovskite‐Based Electron‐Selective Contacts for Silicon Solar Cells

Perovskite‐Based Electron‐Selective Contacts for Silicon Solar Cells

Outstanding Surface Passivation for Highly Efficient Silicon Solar Cells Enabled by Innovative Al_yTiO_x/TiO_xElectron‐Selective Contact Stack

Characterization of the Interfacial Defect Layer in Chalcopyrite Solar Cells by Depth‐Resolved Muon Spin Spectroscopy

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A novel passivating electron contact for high-performance silicon solar cells by ALD Al-doped TiO2

Cited by 31 publications

References 33 publications

Perovskite‐Based Electron‐Selective Contacts for Silicon Solar Cells

Perovskite‐Based Electron‐Selective Contacts for Silicon Solar Cells

Outstanding Surface Passivation for Highly Efficient Silicon Solar Cells Enabled by Innovative AlyTiOx/TiOxElectron‐Selective Contact Stack

Characterization of the Interfacial Defect Layer in Chalcopyrite Solar Cells by Depth‐Resolved Muon Spin Spectroscopy

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Outstanding Surface Passivation for Highly Efficient Silicon Solar Cells Enabled by Innovative Al_yTiO_x/TiO_xElectron‐Selective Contact Stack